27-10-2014, 02:55 PM
Humanity's First Epochal Event(s?): Growing our Brains and Controlling Fire
Chapter summary:
Other than humans, rhesus macaques are Earth's most widespread primates, and both species are generalists whose ability to adapt has been responsible for their success. Rhesus macaques are significantly encephalized, about twice that of dogs and cats, and nearly as much as chimpanzees. Rhesus macaques have what is called Machiavellian social organization, in which everybody is continually vying for rank and power is everything. Those with rhesus power get the most and best food, the best and safest sleeping places, mating privileges, the nicest environments to live in, and endless grooming by subordinates, whom the dominants can beat and harass whenever they want, while those low in the hierarchies get the scraps and are usually the first to succumb to the vagaries of rhesus life, including predation.[449] It is the same energy game that all species play. But even the lowliest macaque will become patriotic cannon fodder if his society faces an external threat, as even a macaque knows that a miserable life is better than no life at all. The violence inflicted seems economically optimized; within a society the violence is mostly harassment, but when rival societies first come in contact, the violence is often lethal, as the initially established dominance can last for lifetimes. Within a society, killing a subordinate does not make economic sense, as that subordinate supports the hierarchy. Potentates rely on slaves. The human smile evolved from the teeth-baring display of monkeys that connotes fear or submission.[450]
For all of their seeming cunning and behaviors right out of The Prince, rhesus monkeys cannot pass the mirror test; they attack their images, as they see themselves as just another rival monkey. Chimpanzees, on the other hand, pass the mirror test, and the threshold of sentience, whatever sentience really is, may not be far removed from the ability to pass the mirror test, or perhaps humanity has not yet achieved it. Capuchin monkeys, considered the most intelligent New World monkeys, have socially based learning, in which the young watch and imitate their elders. Different capuchin societies have different cultures and different tool-using behaviors reflected in different solutions to similar foraging problems.[451] Capuchins, isolated from African and Asian monkeys for about 30 million years, have striking similarities to their Old World counterparts, with female-centric societies and lethal hierarchical politics. As with chimpanzees and humans, ganging up on lone victims is the preferred method, which increases the chance of success and reduces the risk to the murderers.[452] Unlike rhesus monkeys, for instance, capuchin males can help with infant rearing, but they will also kill infants that they did not father, as rhesus, chimpanzees, and gorillas also do (that behavior has been observed in 50 primate species).[453] Those comparisons provide evidence that simian social organization results from the connection between simian biology and environment; their societies formed to solve the problems of feeding, safety, and reproduction.
Chimps and orangutans have distinct cultures and ways of transmitting knowledge, usually confined to observation. They have regional variations in tool use, and orangutans can display startling intelligence in captivity that is not witnessed in the wild, which may be like country bumpkins moving to the city where they can develop their intellects or get a chance to use them.[454] Chimps can negotiate, deceive, hunt in ranked groups, learn sign language, use more than one tool in a process, problem-solve, and engage in other human-like activities. Developmentally, a chimp is ahead of a human until about age two, and chimps can also express empathy.[455] Research has suggested that imitation (performing somebody else's actions) and empathy (feeling what somebody else feels) are related neurologically.[456] Humans, however, are far better than chimps in their social-cognitive skills, which brings in the "theory of mind," which is thinking what others are thinking. This is suspected to be the key developmental trait that set humans apart from their cousins.[457]
Many observable aspects of today's simians probably reflect ancestral traits predating the evolutionary splits that led to humans. A chimpanzee's brain is about 360 cubic centimeters ("ccs") in size, and that gracile australopithecine that probably made those early stone tools had a brain of about 450 ccs. That brain growth reflected millions of years of evolution since the chimpanzee line split, at least a million years of bipedal existence, and hands adapted to manipulating tools. The cognitive and manipulative abilities of the species that made early stone tools seem to have been significantly advanced over chimps. Below is a comparison of the skull of a modern human, and orangutan, a chimpanzee, and a macaque. (Source: Wikimedia Commons)
![[Image: skulls.jpg]](http://www.ahealedplanet.net/skulls.jpg)
The human brain weighs more than three times the orangutan's and chimpanzee's, and more than ten times the macaque's. Beginning about 2.5 million years ago, around when the first stone tools were invented, the human line's jaws became weaker and jaw muscles were no longer attached to the braincase.[458] Some scientists think that that change helped the human line's brain grow.
The rise of humans was dependent on numerous factors, but the most important may have been the ability to increase humanity's collective knowledge. If each invention during human history had to be continually reinvented from scratch, there would not be people today. The cultural transmission of innovations was critical to growing humanity's collective technology, skills, and intelligence. Striking stones to fashion tools was new on Earth, and it was likely invented once, and then proliferated as others learned the skill. The pattern of proliferation of stone tool culture in Africa supports that idea.
Those first stone tools are called pebble tools, and anthropologists have placed the protohumans who made them in the Oldowan culture (also called the Oldowan industry, or Mode 1 on the stone tool scale). The rocks used for Oldowan tools were already nearly the shape needed and were made by banging candidate rocks on a rock "anvil," and the fractured rock's sharp edge was the tool. Those first stone tool makers were largely still the hunted, not hunters, and stone edges would have been like claws and teeth that would have made scavenging predator kills easy in a way that primates had never before experienced. Modern researchers have used Oldowan tools to quickly butcher elephants. Sawing a limb from a predator kill and stealing it would have been quick and easy.[459] Stone tools also crushed bones to extract marrow, and would have made harvesting and processing plant foods far easier.[460]
Below are relics of the five stone tool cultures that scientists have discovered. (Source for all images: Wikimedia Commons)
![[Image: stonetools.jpg]](http://www.ahealedplanet.net/stonetools.jpg)
Scientists today think that above all else, the first stone tools began humanity's Age of Meat. Meat is a nutrient-dense food and is highly prized among wild chimpanzees that use it as a key social tool, and male chimps have used it as payment for sex.[461] The human brain is more than three times the size of a chimpanzee's, but recent research suggests that the human brain's size is normal for its body size, and great ape brains seem relatively small because their bodies became relatively large, possibly due to sexual selection that resulted from vying for mates.[462] Humans developed relatively larger brains and relatively smaller and weaker bodies, which was probably an energy tradeoff; something had to give.[463] Protohumans began relying on brains more than brawn. The studies of brain size, encephalization, neocortex function, intelligence, and their relationships are in their infancy. The current leading hypothesis for the stimulant of simian brain growth is social navigation. Larger brains were needed for navigating increasing social complexity, and not only the number of individuals in a society, but the sophistication of interactions.[464] It is also argued that smarter brains allowed for greater social complexity, in another possible instance of mutually reinforcing positive feedbacks. Societies can perform tasks that individuals cannot. Those Machiavellian rhesus macaques engage in wars and revolutions. They can procure a food source and secure the territory, which creates the energetic means for developing a society. Tool-making may have been a bonus of that enlarged brain needed for social navigation, and walking bipedally coincidentally provided new opportunities for hands. Numerous hypotheses have been proposed to explain the rise of human intelligence, and all proposed dynamics may have had their influences. Brains have very high energy requirements, about 10 times the energy needs of equivalent muscle mass, and primates cannot consciously turn their brains off any more than they can turn their livers off. Few studies have been performed on the relationships between energy, brains, and sleep, but a recent one found that sleep seems to be how brains recharge themselves.[465]
Larger brains had to confer immediate advantages or else they would not have evolved, especially as energy-demanding as they are. Evolutionary pressures ensure that there is no cost without an immediate benefit. As humans have demonstrated, intelligence combined with manipulative ability led to a domination of Earth that no other organism ever achieved. Humans weigh about 50% more than chimpanzees, but human brains are at least 250% heavier. A human brain comprises about 2% of the body's mass, but uses nearly 20% of its energy at rest. Growing an energy-demanding organ was funded with the coin of energy. How did protohumans manage it?
There are a number of possible solutions to obtaining the energy to fuel the growing protohuman brain, and they all fall under these categories:
Studies have shown that humans and chimpanzees have the same basal metabolism, so the first possibility is considered very unlikely in our ancestors, although large brains in general seem to require higher metabolic rates.[466] The subject of reducing energy output has an intriguing hypothesis: bipedal motion allowed humans to move by using less energy than our pre-bipedal ancestors. Human bipedal locomotion requires only a quarter of the energy that chimpanzee locomotion does, and chimps use about a quarter of their metabolism walking, although whether this was a key evolutionary event is controversial.[467] Even though protohumans would have taken advantage of bipedal walking to range farther than chimps (humans can average 11 miles a day, while chimps can only achieve six[468]), thereby using a relatively larger proportion of their energy on locomotion; bipedal locomotion energy savings alone might largely account for the growing brain's energy needs. The Expensive-Tissue Hypothesis was developed to account for the required energy, which proposed that energy to fuel the growing brain came from reducing digestion costs, which was initially provided by eating more meat.[469]
Gorillas and chimpanzees are hindgut fermenters and can digest cellulose; humans cannot. The human digestive tract is only about 60% of the size expected for a primate of our size.[470] Human guts are far smaller than chimp and especially gorilla guts, which process all of that low-calorie foliage. Chimps and gorilla rib cages flare outward from top-to-bottom, like a dress, as did australopithecine rib cages, to accommodate large guts, as shown below.
When chimpanzees eat meat, they put large, tough leaves in their mouths. That helps them overachieve as meat eaters, as their teeth and jaws are poorly adapted for chewing meat. Mountain gorillas eat no meat at all. In the wild, great apes spend about half of their day chewing. Chimpanzees are the most carnivorous great ape, and although meat is the greatest treasure in chimpanzee societies, they often stop eating meat after chewing it for an hour or two and revert to fruit and other softer foods if they can get it. Chimpanzees hunt animals primarily during the dry season when their staple, fruit, is scarce. Chimps have been seen killing monkeys, eating their organs, and then abandoning the carcasses to find more monkeys to kill. Organ meats and intestines are far easier to chew, and a poor meat chewer like a chimpanzee prefers soft meats.[471] Just as chimpanzees prefer soft meats, predators will eat soft organs first and leave the tougher muscle for later, if they eat it at all. It depends on how plentiful the available flesh is, but the pattern across all predator groups is clear: eat the best, first, and leave the lesser quality foods to the end or let scavengers have them. It will always be a cost/benefit decision. All things being equal, the less time and energy needed to eat something, the sooner it will be eaten. If extra time and effort is needed to procure food, then the nutritional reward (primarily in energy) has to be exceptional to justify it. Evolutionary pressures have made animals into excellent accountants.[472] The human sweet tooth is a relic of humanity's fruit-eating ape heritage, and the desire for fatty foods reflects an adaptation to prefer that energy-richest of foods. Fat (made of hydrocarbons) is the ultimate energy windfall of all foods.
A recent study has challenged The Expensive-Tissue Hypothesis, at least as far as robbing energy from the digestive system to fuel the brain.[473] The study compared brain and intestinal size in mammals and found no strong correlation, but there was an inverse correlation between brain size and body fat. But since human fat does not impede our locomotion much, humans have combined both strategies for reducing the risk of starvation. Whales have bucked the trend, also because being fatter does not impede their locomotion and provides energy-conserving insulation. A human infant's brain uses about 75% of its energy, and baby fat seems to be brain protection, so that it does not easily run out of fuel. However, the rapid evolutionary growth of an energy-demanding organ like the human brain seems unique or nearly so in the history of life on Earth, and comparative anatomy studies may have limited explanatory utility. There are great debates today on how fast the human brain grew, what coevolutionary constraints may have limited the brain's development (1, 2, 3), and scientific investigations are in their early days.
About a quarter-million years after Oldowan culture began, a new species appeared called Homo habilis, named by Louis Leakey in 1964. Whether Homo habilis is really the first member of the human genus has been debated ever since. As with all of its primate ancestors, Homo habilis was adapted for tree climbing. Virtually all apes and monkeys sleep in trees, especially those in Africa. Silverback gorillas are about the lone exception, along with some isolated chimps. Homo habilis certainly slept in trees. The predators of African woodlands and grasslands have been formidable for millions of years, and predators of Homo habilis in those days included Dinofelis, Megantereon, and Homotherium. Night camera footage is readily available on the Internet today showing the nighttime behaviors engaged in by hyenas, lions, and others. The African woodlands and plains are extremely dangerous at night, just from roving predators, not to mention being stumbled into by elephants, rhinos, and water buffalos. Today's African hunter-gatherers sleep around the campfire to keep predators and interlopers at bay; a sentinel keeps watch as everybody sleeps in shifts through the twelve-hour nights. They are safer from predation at night in camp than they are in daytime as they roam.[474]
The anatomy of habilines (members of Homo habilis) spoke volumes about their lives. They had brains of about 640 ccs, with an estimated range of 600 to 700 ccs, nearly 50% larger than their australopithecine ancestors and nearly twice that of chimps, and the artifacts they left behind denoted advanced cognitive abilities. They stood about 1.5 meters tall (five feet), and weighed around 50 kilograms (120 pounds). With the first appearance of habilines about 2.3 mya, Oldowan culture spread widely in East Africa, and also radiated to South Africa. Habiline skeletal adaptations to tree climbing meant that they slept there at night, just as their ancestral line did. Their teeth were large, which meant that they heavily chewed their food. Habiline sites have large rock hammers that they pounded food on, to break bones and crack nuts. Those habiline stone hammers may well have also been used to soften meat, roots, and other foods before eating them.[475] Sleeping in trees meant that habilines were preyed on, mostly by big cats. Today, the leopard is the only regular predator of chimpanzees and gorillas, and leopards have developed a taste for humans at times. But if modern studies of chimpanzees are relevant, our ancestors engaged in warfare for the past several million years, and monkeys have wars, so simian intra-species mass killings may have tens of millions of years of heritage. Habilines were not only wary of predators, but also of members of their own species.
Monkeys, apes, and humans have many traits in common, and one is that members of "out-groups" are fair game. Chimpanzees are the only non-human animals today that form ranked hunting parties, and they are also the only ones that form hunting parties to kill members of their own species.[476] Distinct from the killer ape hypothesis, which posits that humans are instinctually violent, the chimpanzee violence hypothesis proposes that chimps only engage in warfare when it makes economic sense: when the benefits of eliminating rivals outweigh the risks/costs. Macaque wars and revolutions appear spontaneously, but chimp wars have calculation behind them, which befits a chimp's advanced cognitive abilities; they plan murderous raids and carry them out. It is quite probable that the advancing toolset of protohumans was used for coalitionary killing when perceived benefits exceeded assessed risks/costs. Just as with other behaviors that humans and chimps have in common, these traits probably also existed in our last common ancestor. Other animals also engage in intra-species violence, which includes spiders when key resources are scarce and contested, and when ant colonies have power imbalances, they can trigger invasion and extermination by the larger colony.[477] But human and chimpanzee warfare is uniquely organized and calculating.
Habilines and australopithecines coexisted, and the last gracile australopiths discovered so far went extinct about 2.0 mya. Robust australopiths survived to about 1.2 mya (1, 2), and habilines disappeared about 1.4 mya, so they overlapped the tenure of a species about which there is no doubt of its genus: Homo erectus, which first appeared about 2.0-1.8 mya, and the first fossils are dated to 1.8 mya. Homo erectus is the first human-line species whose members could pass for humans on a city street, if they dressed up and wore minor prosthetics on their heads and faces. Homo erectus had a protruding nose and was probably relatively hairless, the first of the human line to be that way. That was probably related to shedding heat in new, hot environments, as well as cooling its large brain(molecular data with head and body lice supports arguments that the human line became relatively hairless even before australopiths).[478] There are great controversies about that overlap among those three distinct lines that might all have ancestral relationships. Oldowan culture was a multi-species one. There is plenty of speculation that the rise of Homo habilis and its successors caused the extinction of other hominids, driving them to extinction by competition, predation, warfare, or some combination of them. What is certain is that "competing" protohumans went extinct after coexisting with the human line for hundreds of thousands of years. The suspicion that evolving humans drove their cousins to extinction becomes more common as the timeline progresses toward today.[479]
The fossil record is thin for early humans, and any portrayal of the human family tree of those times always carries the disclaimer that it is speculative.[480] Below is a current depiction of the human family tree, with geographical distributions presented. (Source: Wikimedia Commons)
![[Image: humanev.jpg]](http://www.ahealedplanet.net/humanev.jpg)
and below is one from a leading scientist of human evolution, Christopher Stringer. (Source: Wikimedia Commons)
![[Image: stringer.jpg]](http://www.ahealedplanet.net/stringer.jpg)
With the paucity of fossils, particularly between 2.5 and 1.0 mya, a timeframe in which the bones of only about 50 individuals have been found so far, discoveries are regularly announced that can be promoted as finds that will shake up the human family tree. That recently discovered australopith kept evolving hands better suited for tool-making, in parallel to developing humans, and perhaps is even a human ancestor, which would relegate Homo habilis to an extinct offshoot, not a human ancestor.[481] With such a scanty existing record, such announcements can be more than hyperbole. There are often heated controversies over the dates of fossils and artifacts, in which changing a date can radically alter how the evidence is viewed. Many findings can change from minor curiosity to paradigm-shifting discovery and back again, depending on the dates assigned to them.
The most complete early fossil find for the genus Homo is called Turkana Boy, who lived about 1.5 mya. He was a child or juvenile, and would have stood more than 1.6 meters tall as an adult, about as tall as an average woman today (earlier estimates that he would have been more than 1.8 meters tall (six feet) in adulthood appear overstated today). He is the ultimate Homo erectus find so far, and changes from his ancestral species were substantial. His teeth shrank the most between species in the entire line from the chimp/human split, by about 20%, his jaw shrank as well, and perhaps most importantly, his guts shrank, as his rib cage is nearly modern in being more barrel-shaped than flaring at the bottom. This was also the most dramatic rib cage change in the human line. His hips became narrower and he no longer had the shoulder, arm, and hand adaptations needed for sleeping in trees; he was fully adapted for living on the ground. Here are skeleton comparisons between gorillas, chimpanzees, Homo erectus, and today's humans. (Source: Wikimedia Commons)
![[Image: skeletons.jpg]](http://www.ahealedplanet.net/skeletons.jpg)
Homo erectus may have been the first member of its line since the chimp/human split to leave Africa, and was certainly the first to become widespread. The Homo erectus story is a big one, and covers several subjects pertinent to this essay.
I am taking some liberties in calling Turkana Boy a Homo erectus; he is technically a member of Homo ergaster, which is often considered ancestral to Homo erectus, which is the Asian variant's name. There is great debate regarding how the human family tree branches between Ardi and Homo heidelbergensis. Some call the various erectus-type species all subspecies of Homo erectus, while others argue for several distinct species. I will not stray far from the orthodox narrative here, for good reason. The reconstructed early human tale is based on very limited evidence, but that evidence will only grow over time, and the tools and techniques for using them will become more sophisticated. Although there may be some upcoming radical changes in the view of the early human journey, efforts of countless scientist and fossil hunter lifetimes support the narrative that this essay sketches, and I respect their findings and opinions, even though I acknowledge many limitations. The human ego, it seems, becomes more involved as the story of life on Earth moves closer to its human chapters.
Some further examples of the complexity and debate follow. About when Homo erectus is supposed to have appeared, a fossil formed in a similar location, which was at least contemporary with Homo habilis. Where it fits in the human family tree is unknown at this time, but today it is called Homo rudolfensis. This is perhaps a descendant of Kenyanthropus platyops, which Maeve Leakey (who led the team that discovered it) argued is a member of a new genus. Because there is Neanderthal DNA in the modern human genome, under the classic definition of a species, Neanderthals have been placed within Homo sapiens by some anthropologists. Some small Homo erectus fossils in Georgia were initially classified in their own species, but are now designated as a Homo erectus subspecies. The "hobbit" fossils recently discovered on Flores Island have been widely considered as island-dwarfed Homo erecti, but they have features that suggest that they may have been habilines or even australopithecines, which would dramatically change the current view on the first migrations past Africa. They may well have been Oldowan culture australopiths that migrated from Africa about when Homo erectus did, and they also controlled fire. Similarly, a relative of Homo erectus that precedes Homo heidelbergensis is called Homo antecessor, but may also be a Homo erectus subspecies. The confusion and debate is partly because the differences between those "species" are minor and more on the order of regional variation than any radical change. They perhaps could have all interbred with each other. Other than the "hobbits," there are no great anatomical changes and few noticeable cultural ones among the various specimens for more than a million years of evolution, so I refer to them all as Homo erectus, as do many anthropologists, particularly when writing for the lay audience.[482] For those who want to explore the relatively fine distinctions, the material is readily available for study and can be another useful example of the process of science, if one of the more heated illustrations.
The most-accepted hypothesis today is that Homo erectus evolved from Homo habilis and first appeared in East Africa between 2.0 and 1.8 mya. If those are not the exact species that the human line descended through during those times, our actual ancestors were close cousins. The early Homo erectus adults had brains of about 850 ccs, and some later specimens reached 1,100 ccs, or triple the mass of a chimpanzee's brain. Today's human brain only averages about 1,200 ccs (women 1,130 and men 1,260). Homo erectus, as with other members of the line, had a brain that was another third larger than Homo habilis, and probably was responsible for its relatively sophisticated material culture. But important as was its growing brain, other anatomical changes were more telling. Homo erectus was fully adapted for living on the ground and walking great distances. For the first quarter-million years of Homo erectus's existence, they lived in the Oldowan culture, which used tools and weapons that were little more than rocks with sharpened edges, and probably some shaped sticks. They evolved in a highly dangerous environment and all of their ancestors slept in trees. How could they have slept on the ground? In a word: fire.
More than any other technical innovation, the control of fire marked humanity's rise. In his The Descent of Man, Darwin called making fire humanity's greatest achievement. The only possible exception that he noted was the invention of language. Even today, in our industrialized and technological world, almost all of our energy practices are merely more sophisticated ways of controlling fire. The initial control of fire was at once a social act, a mental act, and a technical act.[483] Although making stone tools represented the big break between the human line and its ancestry, it only allowed apes to mimic what other animals could do. Stone tools represented artificial claws, teeth, and jaws of animals far larger and more capable than apes at killing and eating flesh and bones. Protohumans with stone tools could scavenge more effectively and maybe defend themselves and even attack others, but it was not initially different in kind from what other animals could do, and was a pathetically small advantage when their first stone tools were merely rocks with sharpened edges, about on the order of brass knuckles. Would you want to fend off a lion predation attack (and perhaps multiple lions) with a rock, and at night? Controlling fire was the radical break from all other organisms that ever lived on Earth.
A bonobo named Kanzi built a fire (using matches) and roasted marshmallows on his own, and made Oldowan-style tools after being taught. But those who invented stone tools and the control of fire were the Einsteins and Teslas of their day. Hunter-gatherers today often start fires by banging flint against pyrite stones, which is a combination that produces generous sparks. Habilines probably used such stones when making tools. Even Darwin suggested that that may have been how protohumans discovered how to make fire, as they banged rocks together.[484] I have not seen anybody else advocate it, but as with the likelihood that protohumans learned to make stone tools once and the practice then spread, I consider it very likely that the control of fire was learned only once, and then spread. Richard Wrangham thinks that habilines first controlled fire, which led to the evolution of Homo erectus.[485] He could be right, and my reasoning follows.
First and foremost, I have a very difficult time imagining that Homo erectus could have slept on the ground without something to keep Africa's predators at bay, and I am not the only one.[486] I doubt that slender apes, much smaller than humans, swinging sharpened rocks and sticks at saber-toothed cats, hyenas, and the like (or throwing them) would have done much to scare them off. Those days predated spears, arrows, and other sophisticated weapons by more than a million years. The strongest plausible deterrent is fire, and I doubt that Homo erectus was simply vigilant and the sentry awoke everybody when the cats came and they all scrambled up trees (or lived in large enough groups so that they could mass attack any predators). Those apes certainly could not have outrun them. Cats are ambush predators, and woodland apes sleeping on the ground would have likely been easy meat. Without fire, Homo erectus would have been in the same situation as its ancestors, going back tens of millions of years: they slept in trees and other lofty refuges so that predators could not attack them. But all animals respect and fear fire. Fire is the ultimate protection and weapon for humans, even to this day.
Wrangham made the ability to sleep on the ground a key part of his Cooking Hypothesis. Homo erectus was not only adapted for ground living, its guts and teeth also shrank, which would have reflected eating soft and easy-to-digest food. Along with organ meats, cooked food is the leading candidate for soft foods. If habilines mastered fire, they would have almost immediately used it for cooking.
In the 1990s, Wrangham began to develop his Cooking Hypothesis, which he more fully elucidated in Catching Fire, published in 2009. Wrangham marshaled numerous lines of evidence to support his hypothesis, which was widely pilloried by his colleagues.[487] Wrangham conceded that the archeological record was scarce for the early control of fire, but he countered that evidence for early fires would rarely survive. Most caves last a quarter million years or so; they are made from soft stone, and the geological dynamics that create caves also destroy them. Also, early humans, just like gorillas and chimpanzees today, and even early hunter-gatherers, would have been constantly on the move, never sleeping in the same place twice. If the first fires were made in the African woodlands and grasslands, the evidence would not survive for long, just as the remnants of today's hunter-gatherer fires on the African savanna quickly disappear. The gist of Wrangham's Cooking Hypothesis is this:
Wrangham's hypothesis is more robust and subtle than this essay can do justice to, but I will survey some of the findings, implications, and controversy. Raw food has various nutritional properties that are superior to cooked food, such as vitamins, but because cooked food provides more digestible calories for humans than raw food, it represented an evolutionary advantage. Meat, starches, and seeds are far more digestible when cooked, and are much easier to chew. Today, chimps in Senegal will not eat raw seeds of Afzelia trees, but when a fire passes through the savanna, they search the ground below the Afzelia trees and eat their cooked seeds.[488]
People and animals universally prefer the taste of cooked food over raw, except for fruit, which was designed by the plant to be eaten by animals; no other foods were designed to be eaten and digested (except nectar, blossoms, and mother's milk). The toxins created by cooking, such as Maillard compounds, can cause health problems in humans, including chronic diseases. But cooking also destroys some toxins, making otherwise inedible food palatable. Cooking also reduces collagen, which makes meat tough, to gelatin (called denaturing the protein, when it falls apart), and converts raw starch to a far more digestible form. However, as far as species viability is concerned, humans only have to live long enough to produce offspring. The degenerative diseases (especially artery disease, cancer, and diabetes) that shorten human lives today would have been irrelevant in the ancient past, when virtually nobody lived long enough to die of old age and they could reproduce long before the deleterious effects of cooked food caught up with them. Many detriments of cooking and food processing have only become important to human welfare with the advent of civilization. Cooking would have been an undisputed advantage long ago.
Were the dramatic changes in Turkana Boy's anatomy a result of cooked food, or was Turkana Boy eating organs as his species became hunters instead of hunted, and the stone tools softened up the meat and plant foods so that he did not need to chew as much? Wrangham co-authored a study on shrinking teeth in the human line that began with Homo erectus. It concluded that food processing, cooking in particular, accounted for the effect.[489] Cooked food versus raw food and the number of neurons that can be supported in a brain has been the focus of recent research.[490] The primary reason why Wrangham's hypothesis was initially dismissed was that archeological evidence for fires that long ago is almost nonexistent. When Catching Fire was published, the earliest evidence with wide acceptance only supported fires beginning around 800 kya, where Israel is today, which is more than a million years after Wrangham's estimated timeframe. Wrangham did what all bold scientists do: he made falsifiable predictions. If it turned out that no evidence of early fires was ever found, his hypothesis could begin looking shaky.
Animals can quickly adapt to changing environmental conditions that impact their food supply. For example, in recent studies of Galapagos finches during a severe drought, small-beaked finches largely died out, because large and hard seeds became dominant. The surviving finch population had measurably larger beaks in one year. It took fifteen years of normal conditions for finch beaks to return to their pre-drought length.[491] Wrangham argued that the biological changes attending cooked food would have been immediately evident, and Homo erectus's anatomy presented the most dramatic changes seen in the human line. The only other plausible candidate would have been Homo heidelbergensis, but it was only a more robust version of Homo sapiens.
The derision was loud from Wrangham's colleagues…until evidence of fire being used a million years ago was found at Wonderwerk Cave in South Africa by using new tools and techniques. The chortling is subsiding somewhat and scientists are now looking for the faint evidence, and long-disputed evidence of 1.5-1.7 mya controlled fires is being reconsidered, although his hypothesis is still widely considered as being only "mildly compelling" at best..[492] New tools may push back the control of fire to a time that matches Wrangham's audacious hypothesis. Wrangham cited the Expensive-Tissue Hypothesis as partially supporting the Cooking Hypothesis, but as discussed previously, the energy to power the human brain may not have solely derived from cooked food's energy benefits. Wrangham has cited numerous lines of evidence, one of which is a bird called the honeyguide that has coevolved with humans to find honeybee hives and smoke them out; the humans get the honey and the honeyguide gets the larvae and wax. According to recent molecular evidence, the evolutionary split of the honeyguide from its ancestors happened up to three mya, which supports the early-control-of-fire hypothesis. There is great controversy regarding these subjects, from recent findings that some chimps make ground nests today to scientists making arguments that meat instead of cooking led to the anatomical changes to the social impacts of campfires. This section of this essay will probably be one of the first to be revised in future versions, as new evidence is adduced and new hypotheses are proposed.
Two major events happened soon after Homo erectus appeared, and their sequence seems to support the Cooking Hypotheses. The first of which was the migration of Homo erectus from Africa as early as 2.0-1.9 mya; they spread to Georgia and Java by 1.8 mya (perhaps 1.6 mya in the case of Java), and China by 1.7 mya. It was the first mass migration from Africa by apes since the Miocene, and Homo erectus may have become the first multi-continental member of the human line, and certainly the first widespread one. Favorable climates and a lower Himalaya range and Tibetan Plateau may have encouraged that migration.[493] Unlike Miocene apes that began to migrate from Africa 16.5 mya, there was no unbroken forest to sustain Homo erectus's journey to East Asia. Those Homo erecti migrants would have had to sleep on the ground for much of the journey, and were not adapted for sleeping in trees, as already discussed. From today's viewpoint, it may seem that they were adventurers, but as will also become obvious with the spread of Homo sapiens, in one individual's lifetime, there was probably only modest movement, expanding into the next uninhabited valley or two. Such an expansion happened one valley at a time, one generation at a time, to make it across a continent in a few thousand years for those that could adapt to changing biomes. Migrating at the same latitude would not have presented great climatic issues. As those migrations happened during the ice age, they were along southern Eurasia. There is no evidence yet that Homo erectus ever made it to Australia, probably because of the ocean crossing required for passage.
The other big event happened about 1.8-1.7 mya, when African stone tools took a leap in sophistication, and Acheulean culture (also called Acheulean industry or Mode 2) appeared and lasted for more than a million years. The quintessential Acheulean tool is the hand axe, and the makers used bone, antler, and wood to shape the axes. Some argue that the axes were not really axes at all, but used for other purposes, even including just the leftover core after flakes were removed. Some gigantic hand axes have been discovered that could not have been easily used by human hands, and may have been early status symbols.[494] Not only were axes made, but also flakes, scrapers, cleavers, and other relatively sophisticated tools. There is almost no doubt among anthropologists that Homo erectus invented Acheulean tools and developed them from Oldowan tools. The axes have a very distinctive shape and could even be called a product of craftsmanship, which reflected minds greatly advanced from today's great apes.
A plausible series of events, when fire came first and Acheulean industry second, is that the Homo erecti that traveled to East and Southeast Asia did not have Acheulean tools, but the primitive Oldowan toolset, and the most remote ones never used Acheulean tools. I consider it quite possible that early Homo erecti migrated from Africa (and maybe even an earlier protohuman, if the "hobbits" were descended from habilines or australopiths) wielding fire. Cooking came with it, and hundreds of thousands of years later, those Homo erecti that stayed home in cosmopolitan Africa invented a new level of technology, Acheulean tools, and that culture never made it to the remote corners of East Asia. Some have speculated that those East Asian Homo erecti used bamboo more than stone, which would not be preserved for study today, or that as they moved east they lost the art of making Acheulean tools.[495] I think the likelier explanation is that they never had Acheulean tools, which means that they left Africa before they were invented, but they brought fire with them, which was the essential technology.
The Homo erecti that arrived in East Asia and the islands off of Southeast Asia existed, and virtually no changes are evident in their anatomy or technology for more than 1.5 million years, only to disappear about when Homo sapiens arrived. Like tarsiers finding refuge in the islands near Southeast Asia, those Homo erecti at the far end of the "known" world seem to have lived like country bumpkins for well over one million years, without any outside disturbances or benefits from their cosmopolitan homeland. The foregoing is largely my speculation on the issue, which could collapse like a house of cards with the Next Great Finding, and the lack of evidence for early fires is the biggest hurdle. Like Wrangham, I will follow those investigations of early fire with great interest. I strongly doubt that any species that ever acquired the greatest technology in Earth's history would ever lose it, as it would have quickly become indispensable.
Growing the human brain was about more than energy. There is speculation that meat protein helped human evolutionary brain development, and there is also evidence that oils help. There are surely nutritional requirements besides calories, but calories comprise the vast majority of nutrition. About 80% of what is called human nutrition consists of calories. If animals can obtain enough energy, the other dietary constraints are usually minor issues.
Apes make poor carnivores and are adapted for eating fruit as their staple, and fruit is the ideal human food. The dietary shift to meat, probably out of necessity, came with a price. If humans get more than half of their calories from protein, they will die from protein poisoning.[496] Chimpanzees get about ten percent of their calories from protein today, which is about the same level that humans seem to need, but it is not necessary to get that protein from meat. I have not eaten meat since the 1980s.
Moreover, the rise of the human brain was not only about size, even if the human brain turns out to "only" be a linearly scaled primate brain. The human cerebral cortex is four times the size of a chimp's, and the cerebral cortex is considered to be where all higher human brain functions originate. For all the influences of using hands, tools, cooking, and the like, they largely only laid the foundation for the cerebral cortex to grow. A mystic might say that the growing cerebral cortex allowed for the human brain to host a more sophisticated consciousness, which originates in other dimensions. This is a question largely unanswerable by today's mainstream science, although Black Science probably has some pretty good ideas. As with mainstream scientists, I will not attempt to address that question, at least in this part of the essay. In the final analysis, the cerebral cortex's growth made humans radically different from any other land animal in Earth's history. Cetaceans may have similar levels of brain functioning, perhaps even greater, but they cannot manipulate their environments like humans can, and they cannot make fires. Humans are significantly juvenilized when compared to chimps, for instance; humans retained traits of chimp infants. An infant chimp's flat face appears far closer to a human's than an adult chimp's does. That juvenilization is partly why humans are far weaker, physically, than other great apes. As the human line increasingly relied on its brain, it lost even more of its brawn.
In summary, becoming bipedal had great portent for evolving protohumans, and the suspicion is very strong among scientists that it led to feedback loops in which tool use became advanced, which allowed for a richer diet, which helped lead to larger and more complex brains, which led to more advanced thinking and behaviors, which led to more advanced tools, which led to more acquired energy, better protection, and larger brains, and so it went. But the control of fire was a watershed event. Although better tools improved the viability of early humans, nothing on Earth could challenge fire-wielding humans. With the control of fire, humans never had to worry again about being preyed on, nor as a threat to species viability, except by other humans. Naturally, fire was eventually used for offense instead of defense.
What is fire? That may seem too-elementary a question, but understanding what it is and where it came from is vitally important for understanding the human journey. The first fires were the quick release of stored sunlight energy that life forms, plants in that instance, had used to build themselves as they made their energy budget "decisions," and it was from vegetation that recently died and was dry enough to burn. The energy was released from burning so fast that it became far hotter (because the molecules were violently "pushed" by the reaction that also released photons) than the biological process of making animals warm-blooded. Hot enough in fact that the released photons' wavelengths were short enough (energetic enough) and human eyes could see them, in a phenomenon called flames. Flames are visible side-effects of that intense energy release. The rapid movement of the molecules as they rocketed due to that gre
Chapter summary:
- Macaque social organization
- Chimp and orangutan culture
- Human-line brain begins growing
- First stone tool culture
- Human brain compared to ape brains
- Social navigation and brain requirements
- Energy tradeoffs with brain growth
- Chimp and gorilla diets and digestion
- Appearance of Homo habilis
- Campfires and predators
- Chimp coalitionary killing
- Appearance of Homo erectus
- Extinction of humanity's cousins
- Human evolutionary tree
- Turkana Boy and anatomical changes in Homo erectus
- Controversies over human-line descent
- Control of fire and human-line evolution
- Human-line sleeping on the ground
- Cooking Hypothesis
- First human-line migration from Africa
- Second stone tool culture
- Nutrition and brain development
- What fire is
- Fire as first great human ecosystem robbery
- Non-geological timescale definition of "epochal"
- Imagining where the control of fire and stone tools would lead
- Ice-age impacts on human evolution
- Origin of spoken language
- Bonobo social organization and overcoming male violence
- "Out of Africa" and multiregional theories of human evolution
- One million years of stagnant human culture
- Fertile nexus of Africa, Asia, and Europe
- Appearance of Homo heidelbergensis
- Human transition from hunted to hunter
- Improving Middle Stone Age toolset
- Neanderthals appear
- Neanderthals invent third stone tool culture
- Homo sapiens appears
- Ice-age impacts on human movements
- First Homo sapiens migration past Africa
- DNA evidence for founder population that left Africa
Other than humans, rhesus macaques are Earth's most widespread primates, and both species are generalists whose ability to adapt has been responsible for their success. Rhesus macaques are significantly encephalized, about twice that of dogs and cats, and nearly as much as chimpanzees. Rhesus macaques have what is called Machiavellian social organization, in which everybody is continually vying for rank and power is everything. Those with rhesus power get the most and best food, the best and safest sleeping places, mating privileges, the nicest environments to live in, and endless grooming by subordinates, whom the dominants can beat and harass whenever they want, while those low in the hierarchies get the scraps and are usually the first to succumb to the vagaries of rhesus life, including predation.[449] It is the same energy game that all species play. But even the lowliest macaque will become patriotic cannon fodder if his society faces an external threat, as even a macaque knows that a miserable life is better than no life at all. The violence inflicted seems economically optimized; within a society the violence is mostly harassment, but when rival societies first come in contact, the violence is often lethal, as the initially established dominance can last for lifetimes. Within a society, killing a subordinate does not make economic sense, as that subordinate supports the hierarchy. Potentates rely on slaves. The human smile evolved from the teeth-baring display of monkeys that connotes fear or submission.[450]
For all of their seeming cunning and behaviors right out of The Prince, rhesus monkeys cannot pass the mirror test; they attack their images, as they see themselves as just another rival monkey. Chimpanzees, on the other hand, pass the mirror test, and the threshold of sentience, whatever sentience really is, may not be far removed from the ability to pass the mirror test, or perhaps humanity has not yet achieved it. Capuchin monkeys, considered the most intelligent New World monkeys, have socially based learning, in which the young watch and imitate their elders. Different capuchin societies have different cultures and different tool-using behaviors reflected in different solutions to similar foraging problems.[451] Capuchins, isolated from African and Asian monkeys for about 30 million years, have striking similarities to their Old World counterparts, with female-centric societies and lethal hierarchical politics. As with chimpanzees and humans, ganging up on lone victims is the preferred method, which increases the chance of success and reduces the risk to the murderers.[452] Unlike rhesus monkeys, for instance, capuchin males can help with infant rearing, but they will also kill infants that they did not father, as rhesus, chimpanzees, and gorillas also do (that behavior has been observed in 50 primate species).[453] Those comparisons provide evidence that simian social organization results from the connection between simian biology and environment; their societies formed to solve the problems of feeding, safety, and reproduction.
Chimps and orangutans have distinct cultures and ways of transmitting knowledge, usually confined to observation. They have regional variations in tool use, and orangutans can display startling intelligence in captivity that is not witnessed in the wild, which may be like country bumpkins moving to the city where they can develop their intellects or get a chance to use them.[454] Chimps can negotiate, deceive, hunt in ranked groups, learn sign language, use more than one tool in a process, problem-solve, and engage in other human-like activities. Developmentally, a chimp is ahead of a human until about age two, and chimps can also express empathy.[455] Research has suggested that imitation (performing somebody else's actions) and empathy (feeling what somebody else feels) are related neurologically.[456] Humans, however, are far better than chimps in their social-cognitive skills, which brings in the "theory of mind," which is thinking what others are thinking. This is suspected to be the key developmental trait that set humans apart from their cousins.[457]
Many observable aspects of today's simians probably reflect ancestral traits predating the evolutionary splits that led to humans. A chimpanzee's brain is about 360 cubic centimeters ("ccs") in size, and that gracile australopithecine that probably made those early stone tools had a brain of about 450 ccs. That brain growth reflected millions of years of evolution since the chimpanzee line split, at least a million years of bipedal existence, and hands adapted to manipulating tools. The cognitive and manipulative abilities of the species that made early stone tools seem to have been significantly advanced over chimps. Below is a comparison of the skull of a modern human, and orangutan, a chimpanzee, and a macaque. (Source: Wikimedia Commons)
The human brain weighs more than three times the orangutan's and chimpanzee's, and more than ten times the macaque's. Beginning about 2.5 million years ago, around when the first stone tools were invented, the human line's jaws became weaker and jaw muscles were no longer attached to the braincase.[458] Some scientists think that that change helped the human line's brain grow.
The rise of humans was dependent on numerous factors, but the most important may have been the ability to increase humanity's collective knowledge. If each invention during human history had to be continually reinvented from scratch, there would not be people today. The cultural transmission of innovations was critical to growing humanity's collective technology, skills, and intelligence. Striking stones to fashion tools was new on Earth, and it was likely invented once, and then proliferated as others learned the skill. The pattern of proliferation of stone tool culture in Africa supports that idea.
Those first stone tools are called pebble tools, and anthropologists have placed the protohumans who made them in the Oldowan culture (also called the Oldowan industry, or Mode 1 on the stone tool scale). The rocks used for Oldowan tools were already nearly the shape needed and were made by banging candidate rocks on a rock "anvil," and the fractured rock's sharp edge was the tool. Those first stone tool makers were largely still the hunted, not hunters, and stone edges would have been like claws and teeth that would have made scavenging predator kills easy in a way that primates had never before experienced. Modern researchers have used Oldowan tools to quickly butcher elephants. Sawing a limb from a predator kill and stealing it would have been quick and easy.[459] Stone tools also crushed bones to extract marrow, and would have made harvesting and processing plant foods far easier.[460]
Below are relics of the five stone tool cultures that scientists have discovered. (Source for all images: Wikimedia Commons)
Scientists today think that above all else, the first stone tools began humanity's Age of Meat. Meat is a nutrient-dense food and is highly prized among wild chimpanzees that use it as a key social tool, and male chimps have used it as payment for sex.[461] The human brain is more than three times the size of a chimpanzee's, but recent research suggests that the human brain's size is normal for its body size, and great ape brains seem relatively small because their bodies became relatively large, possibly due to sexual selection that resulted from vying for mates.[462] Humans developed relatively larger brains and relatively smaller and weaker bodies, which was probably an energy tradeoff; something had to give.[463] Protohumans began relying on brains more than brawn. The studies of brain size, encephalization, neocortex function, intelligence, and their relationships are in their infancy. The current leading hypothesis for the stimulant of simian brain growth is social navigation. Larger brains were needed for navigating increasing social complexity, and not only the number of individuals in a society, but the sophistication of interactions.[464] It is also argued that smarter brains allowed for greater social complexity, in another possible instance of mutually reinforcing positive feedbacks. Societies can perform tasks that individuals cannot. Those Machiavellian rhesus macaques engage in wars and revolutions. They can procure a food source and secure the territory, which creates the energetic means for developing a society. Tool-making may have been a bonus of that enlarged brain needed for social navigation, and walking bipedally coincidentally provided new opportunities for hands. Numerous hypotheses have been proposed to explain the rise of human intelligence, and all proposed dynamics may have had their influences. Brains have very high energy requirements, about 10 times the energy needs of equivalent muscle mass, and primates cannot consciously turn their brains off any more than they can turn their livers off. Few studies have been performed on the relationships between energy, brains, and sleep, but a recent one found that sleep seems to be how brains recharge themselves.[465]
Larger brains had to confer immediate advantages or else they would not have evolved, especially as energy-demanding as they are. Evolutionary pressures ensure that there is no cost without an immediate benefit. As humans have demonstrated, intelligence combined with manipulative ability led to a domination of Earth that no other organism ever achieved. Humans weigh about 50% more than chimpanzees, but human brains are at least 250% heavier. A human brain comprises about 2% of the body's mass, but uses nearly 20% of its energy at rest. Growing an energy-demanding organ was funded with the coin of energy. How did protohumans manage it?
There are a number of possible solutions to obtaining the energy to fuel the growing protohuman brain, and they all fall under these categories:
- Increase total energy input;
- Reduce total energy output;
- Rob energy from other tissues and processes; they will either become smaller, more energy efficient, or will be discarded.
Studies have shown that humans and chimpanzees have the same basal metabolism, so the first possibility is considered very unlikely in our ancestors, although large brains in general seem to require higher metabolic rates.[466] The subject of reducing energy output has an intriguing hypothesis: bipedal motion allowed humans to move by using less energy than our pre-bipedal ancestors. Human bipedal locomotion requires only a quarter of the energy that chimpanzee locomotion does, and chimps use about a quarter of their metabolism walking, although whether this was a key evolutionary event is controversial.[467] Even though protohumans would have taken advantage of bipedal walking to range farther than chimps (humans can average 11 miles a day, while chimps can only achieve six[468]), thereby using a relatively larger proportion of their energy on locomotion; bipedal locomotion energy savings alone might largely account for the growing brain's energy needs. The Expensive-Tissue Hypothesis was developed to account for the required energy, which proposed that energy to fuel the growing brain came from reducing digestion costs, which was initially provided by eating more meat.[469]
Gorillas and chimpanzees are hindgut fermenters and can digest cellulose; humans cannot. The human digestive tract is only about 60% of the size expected for a primate of our size.[470] Human guts are far smaller than chimp and especially gorilla guts, which process all of that low-calorie foliage. Chimps and gorilla rib cages flare outward from top-to-bottom, like a dress, as did australopithecine rib cages, to accommodate large guts, as shown below.
When chimpanzees eat meat, they put large, tough leaves in their mouths. That helps them overachieve as meat eaters, as their teeth and jaws are poorly adapted for chewing meat. Mountain gorillas eat no meat at all. In the wild, great apes spend about half of their day chewing. Chimpanzees are the most carnivorous great ape, and although meat is the greatest treasure in chimpanzee societies, they often stop eating meat after chewing it for an hour or two and revert to fruit and other softer foods if they can get it. Chimpanzees hunt animals primarily during the dry season when their staple, fruit, is scarce. Chimps have been seen killing monkeys, eating their organs, and then abandoning the carcasses to find more monkeys to kill. Organ meats and intestines are far easier to chew, and a poor meat chewer like a chimpanzee prefers soft meats.[471] Just as chimpanzees prefer soft meats, predators will eat soft organs first and leave the tougher muscle for later, if they eat it at all. It depends on how plentiful the available flesh is, but the pattern across all predator groups is clear: eat the best, first, and leave the lesser quality foods to the end or let scavengers have them. It will always be a cost/benefit decision. All things being equal, the less time and energy needed to eat something, the sooner it will be eaten. If extra time and effort is needed to procure food, then the nutritional reward (primarily in energy) has to be exceptional to justify it. Evolutionary pressures have made animals into excellent accountants.[472] The human sweet tooth is a relic of humanity's fruit-eating ape heritage, and the desire for fatty foods reflects an adaptation to prefer that energy-richest of foods. Fat (made of hydrocarbons) is the ultimate energy windfall of all foods.
A recent study has challenged The Expensive-Tissue Hypothesis, at least as far as robbing energy from the digestive system to fuel the brain.[473] The study compared brain and intestinal size in mammals and found no strong correlation, but there was an inverse correlation between brain size and body fat. But since human fat does not impede our locomotion much, humans have combined both strategies for reducing the risk of starvation. Whales have bucked the trend, also because being fatter does not impede their locomotion and provides energy-conserving insulation. A human infant's brain uses about 75% of its energy, and baby fat seems to be brain protection, so that it does not easily run out of fuel. However, the rapid evolutionary growth of an energy-demanding organ like the human brain seems unique or nearly so in the history of life on Earth, and comparative anatomy studies may have limited explanatory utility. There are great debates today on how fast the human brain grew, what coevolutionary constraints may have limited the brain's development (1, 2, 3), and scientific investigations are in their early days.
About a quarter-million years after Oldowan culture began, a new species appeared called Homo habilis, named by Louis Leakey in 1964. Whether Homo habilis is really the first member of the human genus has been debated ever since. As with all of its primate ancestors, Homo habilis was adapted for tree climbing. Virtually all apes and monkeys sleep in trees, especially those in Africa. Silverback gorillas are about the lone exception, along with some isolated chimps. Homo habilis certainly slept in trees. The predators of African woodlands and grasslands have been formidable for millions of years, and predators of Homo habilis in those days included Dinofelis, Megantereon, and Homotherium. Night camera footage is readily available on the Internet today showing the nighttime behaviors engaged in by hyenas, lions, and others. The African woodlands and plains are extremely dangerous at night, just from roving predators, not to mention being stumbled into by elephants, rhinos, and water buffalos. Today's African hunter-gatherers sleep around the campfire to keep predators and interlopers at bay; a sentinel keeps watch as everybody sleeps in shifts through the twelve-hour nights. They are safer from predation at night in camp than they are in daytime as they roam.[474]
The anatomy of habilines (members of Homo habilis) spoke volumes about their lives. They had brains of about 640 ccs, with an estimated range of 600 to 700 ccs, nearly 50% larger than their australopithecine ancestors and nearly twice that of chimps, and the artifacts they left behind denoted advanced cognitive abilities. They stood about 1.5 meters tall (five feet), and weighed around 50 kilograms (120 pounds). With the first appearance of habilines about 2.3 mya, Oldowan culture spread widely in East Africa, and also radiated to South Africa. Habiline skeletal adaptations to tree climbing meant that they slept there at night, just as their ancestral line did. Their teeth were large, which meant that they heavily chewed their food. Habiline sites have large rock hammers that they pounded food on, to break bones and crack nuts. Those habiline stone hammers may well have also been used to soften meat, roots, and other foods before eating them.[475] Sleeping in trees meant that habilines were preyed on, mostly by big cats. Today, the leopard is the only regular predator of chimpanzees and gorillas, and leopards have developed a taste for humans at times. But if modern studies of chimpanzees are relevant, our ancestors engaged in warfare for the past several million years, and monkeys have wars, so simian intra-species mass killings may have tens of millions of years of heritage. Habilines were not only wary of predators, but also of members of their own species.
Monkeys, apes, and humans have many traits in common, and one is that members of "out-groups" are fair game. Chimpanzees are the only non-human animals today that form ranked hunting parties, and they are also the only ones that form hunting parties to kill members of their own species.[476] Distinct from the killer ape hypothesis, which posits that humans are instinctually violent, the chimpanzee violence hypothesis proposes that chimps only engage in warfare when it makes economic sense: when the benefits of eliminating rivals outweigh the risks/costs. Macaque wars and revolutions appear spontaneously, but chimp wars have calculation behind them, which befits a chimp's advanced cognitive abilities; they plan murderous raids and carry them out. It is quite probable that the advancing toolset of protohumans was used for coalitionary killing when perceived benefits exceeded assessed risks/costs. Just as with other behaviors that humans and chimps have in common, these traits probably also existed in our last common ancestor. Other animals also engage in intra-species violence, which includes spiders when key resources are scarce and contested, and when ant colonies have power imbalances, they can trigger invasion and extermination by the larger colony.[477] But human and chimpanzee warfare is uniquely organized and calculating.
Habilines and australopithecines coexisted, and the last gracile australopiths discovered so far went extinct about 2.0 mya. Robust australopiths survived to about 1.2 mya (1, 2), and habilines disappeared about 1.4 mya, so they overlapped the tenure of a species about which there is no doubt of its genus: Homo erectus, which first appeared about 2.0-1.8 mya, and the first fossils are dated to 1.8 mya. Homo erectus is the first human-line species whose members could pass for humans on a city street, if they dressed up and wore minor prosthetics on their heads and faces. Homo erectus had a protruding nose and was probably relatively hairless, the first of the human line to be that way. That was probably related to shedding heat in new, hot environments, as well as cooling its large brain(molecular data with head and body lice supports arguments that the human line became relatively hairless even before australopiths).[478] There are great controversies about that overlap among those three distinct lines that might all have ancestral relationships. Oldowan culture was a multi-species one. There is plenty of speculation that the rise of Homo habilis and its successors caused the extinction of other hominids, driving them to extinction by competition, predation, warfare, or some combination of them. What is certain is that "competing" protohumans went extinct after coexisting with the human line for hundreds of thousands of years. The suspicion that evolving humans drove their cousins to extinction becomes more common as the timeline progresses toward today.[479]
The fossil record is thin for early humans, and any portrayal of the human family tree of those times always carries the disclaimer that it is speculative.[480] Below is a current depiction of the human family tree, with geographical distributions presented. (Source: Wikimedia Commons)
and below is one from a leading scientist of human evolution, Christopher Stringer. (Source: Wikimedia Commons)
With the paucity of fossils, particularly between 2.5 and 1.0 mya, a timeframe in which the bones of only about 50 individuals have been found so far, discoveries are regularly announced that can be promoted as finds that will shake up the human family tree. That recently discovered australopith kept evolving hands better suited for tool-making, in parallel to developing humans, and perhaps is even a human ancestor, which would relegate Homo habilis to an extinct offshoot, not a human ancestor.[481] With such a scanty existing record, such announcements can be more than hyperbole. There are often heated controversies over the dates of fossils and artifacts, in which changing a date can radically alter how the evidence is viewed. Many findings can change from minor curiosity to paradigm-shifting discovery and back again, depending on the dates assigned to them.
The most complete early fossil find for the genus Homo is called Turkana Boy, who lived about 1.5 mya. He was a child or juvenile, and would have stood more than 1.6 meters tall as an adult, about as tall as an average woman today (earlier estimates that he would have been more than 1.8 meters tall (six feet) in adulthood appear overstated today). He is the ultimate Homo erectus find so far, and changes from his ancestral species were substantial. His teeth shrank the most between species in the entire line from the chimp/human split, by about 20%, his jaw shrank as well, and perhaps most importantly, his guts shrank, as his rib cage is nearly modern in being more barrel-shaped than flaring at the bottom. This was also the most dramatic rib cage change in the human line. His hips became narrower and he no longer had the shoulder, arm, and hand adaptations needed for sleeping in trees; he was fully adapted for living on the ground. Here are skeleton comparisons between gorillas, chimpanzees, Homo erectus, and today's humans. (Source: Wikimedia Commons)
Homo erectus may have been the first member of its line since the chimp/human split to leave Africa, and was certainly the first to become widespread. The Homo erectus story is a big one, and covers several subjects pertinent to this essay.
I am taking some liberties in calling Turkana Boy a Homo erectus; he is technically a member of Homo ergaster, which is often considered ancestral to Homo erectus, which is the Asian variant's name. There is great debate regarding how the human family tree branches between Ardi and Homo heidelbergensis. Some call the various erectus-type species all subspecies of Homo erectus, while others argue for several distinct species. I will not stray far from the orthodox narrative here, for good reason. The reconstructed early human tale is based on very limited evidence, but that evidence will only grow over time, and the tools and techniques for using them will become more sophisticated. Although there may be some upcoming radical changes in the view of the early human journey, efforts of countless scientist and fossil hunter lifetimes support the narrative that this essay sketches, and I respect their findings and opinions, even though I acknowledge many limitations. The human ego, it seems, becomes more involved as the story of life on Earth moves closer to its human chapters.
Some further examples of the complexity and debate follow. About when Homo erectus is supposed to have appeared, a fossil formed in a similar location, which was at least contemporary with Homo habilis. Where it fits in the human family tree is unknown at this time, but today it is called Homo rudolfensis. This is perhaps a descendant of Kenyanthropus platyops, which Maeve Leakey (who led the team that discovered it) argued is a member of a new genus. Because there is Neanderthal DNA in the modern human genome, under the classic definition of a species, Neanderthals have been placed within Homo sapiens by some anthropologists. Some small Homo erectus fossils in Georgia were initially classified in their own species, but are now designated as a Homo erectus subspecies. The "hobbit" fossils recently discovered on Flores Island have been widely considered as island-dwarfed Homo erecti, but they have features that suggest that they may have been habilines or even australopithecines, which would dramatically change the current view on the first migrations past Africa. They may well have been Oldowan culture australopiths that migrated from Africa about when Homo erectus did, and they also controlled fire. Similarly, a relative of Homo erectus that precedes Homo heidelbergensis is called Homo antecessor, but may also be a Homo erectus subspecies. The confusion and debate is partly because the differences between those "species" are minor and more on the order of regional variation than any radical change. They perhaps could have all interbred with each other. Other than the "hobbits," there are no great anatomical changes and few noticeable cultural ones among the various specimens for more than a million years of evolution, so I refer to them all as Homo erectus, as do many anthropologists, particularly when writing for the lay audience.[482] For those who want to explore the relatively fine distinctions, the material is readily available for study and can be another useful example of the process of science, if one of the more heated illustrations.
The most-accepted hypothesis today is that Homo erectus evolved from Homo habilis and first appeared in East Africa between 2.0 and 1.8 mya. If those are not the exact species that the human line descended through during those times, our actual ancestors were close cousins. The early Homo erectus adults had brains of about 850 ccs, and some later specimens reached 1,100 ccs, or triple the mass of a chimpanzee's brain. Today's human brain only averages about 1,200 ccs (women 1,130 and men 1,260). Homo erectus, as with other members of the line, had a brain that was another third larger than Homo habilis, and probably was responsible for its relatively sophisticated material culture. But important as was its growing brain, other anatomical changes were more telling. Homo erectus was fully adapted for living on the ground and walking great distances. For the first quarter-million years of Homo erectus's existence, they lived in the Oldowan culture, which used tools and weapons that were little more than rocks with sharpened edges, and probably some shaped sticks. They evolved in a highly dangerous environment and all of their ancestors slept in trees. How could they have slept on the ground? In a word: fire.
More than any other technical innovation, the control of fire marked humanity's rise. In his The Descent of Man, Darwin called making fire humanity's greatest achievement. The only possible exception that he noted was the invention of language. Even today, in our industrialized and technological world, almost all of our energy practices are merely more sophisticated ways of controlling fire. The initial control of fire was at once a social act, a mental act, and a technical act.[483] Although making stone tools represented the big break between the human line and its ancestry, it only allowed apes to mimic what other animals could do. Stone tools represented artificial claws, teeth, and jaws of animals far larger and more capable than apes at killing and eating flesh and bones. Protohumans with stone tools could scavenge more effectively and maybe defend themselves and even attack others, but it was not initially different in kind from what other animals could do, and was a pathetically small advantage when their first stone tools were merely rocks with sharpened edges, about on the order of brass knuckles. Would you want to fend off a lion predation attack (and perhaps multiple lions) with a rock, and at night? Controlling fire was the radical break from all other organisms that ever lived on Earth.
A bonobo named Kanzi built a fire (using matches) and roasted marshmallows on his own, and made Oldowan-style tools after being taught. But those who invented stone tools and the control of fire were the Einsteins and Teslas of their day. Hunter-gatherers today often start fires by banging flint against pyrite stones, which is a combination that produces generous sparks. Habilines probably used such stones when making tools. Even Darwin suggested that that may have been how protohumans discovered how to make fire, as they banged rocks together.[484] I have not seen anybody else advocate it, but as with the likelihood that protohumans learned to make stone tools once and the practice then spread, I consider it very likely that the control of fire was learned only once, and then spread. Richard Wrangham thinks that habilines first controlled fire, which led to the evolution of Homo erectus.[485] He could be right, and my reasoning follows.
First and foremost, I have a very difficult time imagining that Homo erectus could have slept on the ground without something to keep Africa's predators at bay, and I am not the only one.[486] I doubt that slender apes, much smaller than humans, swinging sharpened rocks and sticks at saber-toothed cats, hyenas, and the like (or throwing them) would have done much to scare them off. Those days predated spears, arrows, and other sophisticated weapons by more than a million years. The strongest plausible deterrent is fire, and I doubt that Homo erectus was simply vigilant and the sentry awoke everybody when the cats came and they all scrambled up trees (or lived in large enough groups so that they could mass attack any predators). Those apes certainly could not have outrun them. Cats are ambush predators, and woodland apes sleeping on the ground would have likely been easy meat. Without fire, Homo erectus would have been in the same situation as its ancestors, going back tens of millions of years: they slept in trees and other lofty refuges so that predators could not attack them. But all animals respect and fear fire. Fire is the ultimate protection and weapon for humans, even to this day.
Wrangham made the ability to sleep on the ground a key part of his Cooking Hypothesis. Homo erectus was not only adapted for ground living, its guts and teeth also shrank, which would have reflected eating soft and easy-to-digest food. Along with organ meats, cooked food is the leading candidate for soft foods. If habilines mastered fire, they would have almost immediately used it for cooking.
In the 1990s, Wrangham began to develop his Cooking Hypothesis, which he more fully elucidated in Catching Fire, published in 2009. Wrangham marshaled numerous lines of evidence to support his hypothesis, which was widely pilloried by his colleagues.[487] Wrangham conceded that the archeological record was scarce for the early control of fire, but he countered that evidence for early fires would rarely survive. Most caves last a quarter million years or so; they are made from soft stone, and the geological dynamics that create caves also destroy them. Also, early humans, just like gorillas and chimpanzees today, and even early hunter-gatherers, would have been constantly on the move, never sleeping in the same place twice. If the first fires were made in the African woodlands and grasslands, the evidence would not survive for long, just as the remnants of today's hunter-gatherer fires on the African savanna quickly disappear. The gist of Wrangham's Cooking Hypothesis is this:
- Humans cannot solely subsist today on raw food (they cannot get enough calories by eating raw food), but need their food cooked, and all human societies cook their food;
- Cooked food reduces the energy required to digest food and also allows more calories to be absorbed from food, sometimes greatly more, such as doubling;
- Anatomical changes, beginning with Homo erectus and perhaps even earlier, provide evidence that humans have cooked their food for a very long time, up to two million years; the control of fire may be responsible for the appearance of Homo erectus;
- The control of fire allowed Homo erectus to leave the trees and sleep on the ground, which was a first for the human line (or perhaps habilines or australopiths were the first to sleep on the ground with fire, but Homo erectus was the first human-line member biologically adapted to it);
- The energy boost from cooked food helped fuel the continued expansion of the human brain, from habilines to today's humans;
- Cooking reduced chewing time from the six hours per day that other great apes chew to less than an hour for humans; this allowed humans to pursue other activities with their enlarged brain, and was one of the positive feedback loops that led to modern humans;
- Fire became the center of human social life after it was controlled, and the changes attending that development profoundly affected the human journey.
Wrangham's hypothesis is more robust and subtle than this essay can do justice to, but I will survey some of the findings, implications, and controversy. Raw food has various nutritional properties that are superior to cooked food, such as vitamins, but because cooked food provides more digestible calories for humans than raw food, it represented an evolutionary advantage. Meat, starches, and seeds are far more digestible when cooked, and are much easier to chew. Today, chimps in Senegal will not eat raw seeds of Afzelia trees, but when a fire passes through the savanna, they search the ground below the Afzelia trees and eat their cooked seeds.[488]
People and animals universally prefer the taste of cooked food over raw, except for fruit, which was designed by the plant to be eaten by animals; no other foods were designed to be eaten and digested (except nectar, blossoms, and mother's milk). The toxins created by cooking, such as Maillard compounds, can cause health problems in humans, including chronic diseases. But cooking also destroys some toxins, making otherwise inedible food palatable. Cooking also reduces collagen, which makes meat tough, to gelatin (called denaturing the protein, when it falls apart), and converts raw starch to a far more digestible form. However, as far as species viability is concerned, humans only have to live long enough to produce offspring. The degenerative diseases (especially artery disease, cancer, and diabetes) that shorten human lives today would have been irrelevant in the ancient past, when virtually nobody lived long enough to die of old age and they could reproduce long before the deleterious effects of cooked food caught up with them. Many detriments of cooking and food processing have only become important to human welfare with the advent of civilization. Cooking would have been an undisputed advantage long ago.
Were the dramatic changes in Turkana Boy's anatomy a result of cooked food, or was Turkana Boy eating organs as his species became hunters instead of hunted, and the stone tools softened up the meat and plant foods so that he did not need to chew as much? Wrangham co-authored a study on shrinking teeth in the human line that began with Homo erectus. It concluded that food processing, cooking in particular, accounted for the effect.[489] Cooked food versus raw food and the number of neurons that can be supported in a brain has been the focus of recent research.[490] The primary reason why Wrangham's hypothesis was initially dismissed was that archeological evidence for fires that long ago is almost nonexistent. When Catching Fire was published, the earliest evidence with wide acceptance only supported fires beginning around 800 kya, where Israel is today, which is more than a million years after Wrangham's estimated timeframe. Wrangham did what all bold scientists do: he made falsifiable predictions. If it turned out that no evidence of early fires was ever found, his hypothesis could begin looking shaky.
Animals can quickly adapt to changing environmental conditions that impact their food supply. For example, in recent studies of Galapagos finches during a severe drought, small-beaked finches largely died out, because large and hard seeds became dominant. The surviving finch population had measurably larger beaks in one year. It took fifteen years of normal conditions for finch beaks to return to their pre-drought length.[491] Wrangham argued that the biological changes attending cooked food would have been immediately evident, and Homo erectus's anatomy presented the most dramatic changes seen in the human line. The only other plausible candidate would have been Homo heidelbergensis, but it was only a more robust version of Homo sapiens.
The derision was loud from Wrangham's colleagues…until evidence of fire being used a million years ago was found at Wonderwerk Cave in South Africa by using new tools and techniques. The chortling is subsiding somewhat and scientists are now looking for the faint evidence, and long-disputed evidence of 1.5-1.7 mya controlled fires is being reconsidered, although his hypothesis is still widely considered as being only "mildly compelling" at best..[492] New tools may push back the control of fire to a time that matches Wrangham's audacious hypothesis. Wrangham cited the Expensive-Tissue Hypothesis as partially supporting the Cooking Hypothesis, but as discussed previously, the energy to power the human brain may not have solely derived from cooked food's energy benefits. Wrangham has cited numerous lines of evidence, one of which is a bird called the honeyguide that has coevolved with humans to find honeybee hives and smoke them out; the humans get the honey and the honeyguide gets the larvae and wax. According to recent molecular evidence, the evolutionary split of the honeyguide from its ancestors happened up to three mya, which supports the early-control-of-fire hypothesis. There is great controversy regarding these subjects, from recent findings that some chimps make ground nests today to scientists making arguments that meat instead of cooking led to the anatomical changes to the social impacts of campfires. This section of this essay will probably be one of the first to be revised in future versions, as new evidence is adduced and new hypotheses are proposed.
Two major events happened soon after Homo erectus appeared, and their sequence seems to support the Cooking Hypotheses. The first of which was the migration of Homo erectus from Africa as early as 2.0-1.9 mya; they spread to Georgia and Java by 1.8 mya (perhaps 1.6 mya in the case of Java), and China by 1.7 mya. It was the first mass migration from Africa by apes since the Miocene, and Homo erectus may have become the first multi-continental member of the human line, and certainly the first widespread one. Favorable climates and a lower Himalaya range and Tibetan Plateau may have encouraged that migration.[493] Unlike Miocene apes that began to migrate from Africa 16.5 mya, there was no unbroken forest to sustain Homo erectus's journey to East Asia. Those Homo erecti migrants would have had to sleep on the ground for much of the journey, and were not adapted for sleeping in trees, as already discussed. From today's viewpoint, it may seem that they were adventurers, but as will also become obvious with the spread of Homo sapiens, in one individual's lifetime, there was probably only modest movement, expanding into the next uninhabited valley or two. Such an expansion happened one valley at a time, one generation at a time, to make it across a continent in a few thousand years for those that could adapt to changing biomes. Migrating at the same latitude would not have presented great climatic issues. As those migrations happened during the ice age, they were along southern Eurasia. There is no evidence yet that Homo erectus ever made it to Australia, probably because of the ocean crossing required for passage.
The other big event happened about 1.8-1.7 mya, when African stone tools took a leap in sophistication, and Acheulean culture (also called Acheulean industry or Mode 2) appeared and lasted for more than a million years. The quintessential Acheulean tool is the hand axe, and the makers used bone, antler, and wood to shape the axes. Some argue that the axes were not really axes at all, but used for other purposes, even including just the leftover core after flakes were removed. Some gigantic hand axes have been discovered that could not have been easily used by human hands, and may have been early status symbols.[494] Not only were axes made, but also flakes, scrapers, cleavers, and other relatively sophisticated tools. There is almost no doubt among anthropologists that Homo erectus invented Acheulean tools and developed them from Oldowan tools. The axes have a very distinctive shape and could even be called a product of craftsmanship, which reflected minds greatly advanced from today's great apes.
A plausible series of events, when fire came first and Acheulean industry second, is that the Homo erecti that traveled to East and Southeast Asia did not have Acheulean tools, but the primitive Oldowan toolset, and the most remote ones never used Acheulean tools. I consider it quite possible that early Homo erecti migrated from Africa (and maybe even an earlier protohuman, if the "hobbits" were descended from habilines or australopiths) wielding fire. Cooking came with it, and hundreds of thousands of years later, those Homo erecti that stayed home in cosmopolitan Africa invented a new level of technology, Acheulean tools, and that culture never made it to the remote corners of East Asia. Some have speculated that those East Asian Homo erecti used bamboo more than stone, which would not be preserved for study today, or that as they moved east they lost the art of making Acheulean tools.[495] I think the likelier explanation is that they never had Acheulean tools, which means that they left Africa before they were invented, but they brought fire with them, which was the essential technology.
The Homo erecti that arrived in East Asia and the islands off of Southeast Asia existed, and virtually no changes are evident in their anatomy or technology for more than 1.5 million years, only to disappear about when Homo sapiens arrived. Like tarsiers finding refuge in the islands near Southeast Asia, those Homo erecti at the far end of the "known" world seem to have lived like country bumpkins for well over one million years, without any outside disturbances or benefits from their cosmopolitan homeland. The foregoing is largely my speculation on the issue, which could collapse like a house of cards with the Next Great Finding, and the lack of evidence for early fires is the biggest hurdle. Like Wrangham, I will follow those investigations of early fire with great interest. I strongly doubt that any species that ever acquired the greatest technology in Earth's history would ever lose it, as it would have quickly become indispensable.
Growing the human brain was about more than energy. There is speculation that meat protein helped human evolutionary brain development, and there is also evidence that oils help. There are surely nutritional requirements besides calories, but calories comprise the vast majority of nutrition. About 80% of what is called human nutrition consists of calories. If animals can obtain enough energy, the other dietary constraints are usually minor issues.
Apes make poor carnivores and are adapted for eating fruit as their staple, and fruit is the ideal human food. The dietary shift to meat, probably out of necessity, came with a price. If humans get more than half of their calories from protein, they will die from protein poisoning.[496] Chimpanzees get about ten percent of their calories from protein today, which is about the same level that humans seem to need, but it is not necessary to get that protein from meat. I have not eaten meat since the 1980s.
Moreover, the rise of the human brain was not only about size, even if the human brain turns out to "only" be a linearly scaled primate brain. The human cerebral cortex is four times the size of a chimp's, and the cerebral cortex is considered to be where all higher human brain functions originate. For all the influences of using hands, tools, cooking, and the like, they largely only laid the foundation for the cerebral cortex to grow. A mystic might say that the growing cerebral cortex allowed for the human brain to host a more sophisticated consciousness, which originates in other dimensions. This is a question largely unanswerable by today's mainstream science, although Black Science probably has some pretty good ideas. As with mainstream scientists, I will not attempt to address that question, at least in this part of the essay. In the final analysis, the cerebral cortex's growth made humans radically different from any other land animal in Earth's history. Cetaceans may have similar levels of brain functioning, perhaps even greater, but they cannot manipulate their environments like humans can, and they cannot make fires. Humans are significantly juvenilized when compared to chimps, for instance; humans retained traits of chimp infants. An infant chimp's flat face appears far closer to a human's than an adult chimp's does. That juvenilization is partly why humans are far weaker, physically, than other great apes. As the human line increasingly relied on its brain, it lost even more of its brawn.
In summary, becoming bipedal had great portent for evolving protohumans, and the suspicion is very strong among scientists that it led to feedback loops in which tool use became advanced, which allowed for a richer diet, which helped lead to larger and more complex brains, which led to more advanced thinking and behaviors, which led to more advanced tools, which led to more acquired energy, better protection, and larger brains, and so it went. But the control of fire was a watershed event. Although better tools improved the viability of early humans, nothing on Earth could challenge fire-wielding humans. With the control of fire, humans never had to worry again about being preyed on, nor as a threat to species viability, except by other humans. Naturally, fire was eventually used for offense instead of defense.
What is fire? That may seem too-elementary a question, but understanding what it is and where it came from is vitally important for understanding the human journey. The first fires were the quick release of stored sunlight energy that life forms, plants in that instance, had used to build themselves as they made their energy budget "decisions," and it was from vegetation that recently died and was dry enough to burn. The energy was released from burning so fast that it became far hotter (because the molecules were violently "pushed" by the reaction that also released photons) than the biological process of making animals warm-blooded. Hot enough in fact that the released photons' wavelengths were short enough (energetic enough) and human eyes could see them, in a phenomenon called flames. Flames are visible side-effects of that intense energy release. The rapid movement of the molecules as they rocketed due to that gre
"The philosophers have only interpreted the world, in various ways. The point, however, is to change it." Karl Marx
"He would, wouldn't he?" Mandy Rice-Davies. When asked in court whether she knew that Lord Astor had denied having sex with her.
“I think it would be a good idea” Ghandi, when asked about Western Civilisation.
"He would, wouldn't he?" Mandy Rice-Davies. When asked in court whether she knew that Lord Astor had denied having sex with her.
“I think it would be a good idea” Ghandi, when asked about Western Civilisation.