Evolution of the human brain

The development of the human brain is likely the most amazing event in the history of evolution. In a mere 2 million years we evolved from bipedal Chimpanzees to modern humans. Genetically we share 98% of our genes with our cousins, the apes. So, why did this brain expansion happen to us and not our cousins? Why have modern apes remained essentially unchanged during the entire evolution of humans? Their bodies are much the same as fossil apes and their brains are little changed. Although man's brain has evolved, he has yet to produce an actual theory about human brain evolution, but there are many interesting speculations out there that we'll discuss today.

First, let's review the evolution of man, Homo sapiens. Homo meaning man, and sapiens meaning wise. Monkeys, apes, and humans are all in the order primates. Monkeys include all long-tailed primates such as baboons and tamarins. Apes include all tailless primates such as chimpanzees and gorillas. Humans evolved from this ape line and both humans and apes today are in the family called Hominidae.

Ten to twenty million years ago, during the Miocene geological epoch-before man and before pre-humans-the African rain forest provided ape species with a steady, relatively abundant supply of food. Foraging over a limited area, primarily for fruit and nutritious leaves, was sufficient to support groups of apes. The rain forest was relatively safe from large predators that roamed the nearby grasslands, except maybe for an occasional leopard.

Rain forest apes appear to have evolved little over millions of years. They were not threatened. They had food. There was no need for change. But about 9 million years ago the ape line changed. The gorilla line separated from the other Hominidae and then about 6 million years ago the chimpanzee line separated from the pre-human line.

Here's what happened. In the late Miocene epoch, the African climate became more arid and more variable; grassy woodlands expanded and the rain forest habitat the apes were accustomed to became more restricted. Some apes began to forage out into these expanding arid woodlands.

Fossil evidence suggests that early bipedal hominids, apes that walked upright on two feet, may have evolved in this new arid woodland environment. As these hominids spent more time foraging in the woodlands, natural selection would have then favored apes that could walk and run over larger areas. The rain forest apes were better adapted to climbing trees, but the foot bones, leg bones, and joints of these arid woodlands apes evolved and became better adapted for walking and running than those of the rain forest hominids.

The human foot, besides our brain, is one of the most evolved features humans have over apes. As these pre-humans became more terrestrial, or more land-dwelling as opposed to tree-dwelling, their arms and hands also became better adapted for carrying food, using tools, and eventually developing weapons. Perhaps this was the spark that ignited the evolution of the brain.

So, our ape ancestors existed in African rain forests for millions of years and then, over a relatively short period of time, some of these apes diverged into land-dwelling pre-humans that walked upright as we do. These bipedal hominid pre-humans were in the Genus Australopithecus. Richard Leaky's famous "Lucy" was among these. Then the Genus Homo evolved about 2.5 million years ago.
The main reason this new Genus name was given was because of the pre-humans use of stone tools and it is here that the Stone Age begins as does advancement in brain size that we'll talk about in just a minute. Now, earlier pre-humans probably also used tools, most likely made from bone and wood, but stone tools gave Homo habilis, the first Homo pre-human, the edge it needed to prosper in hostile environments previously too formidable for primates. H. habilis is thought to have utilized simple stone flakes as tools. Though these stone flakes were primitive by modern standards, they were more advanced than any tools that had previously existed.
Now, it actually remains quite controversial whether H. habilis was actually the first hominid to master stone-tool technology. The recent discovery of Australopithecus garhi dating 2.6 million years ago was found along with stone-tool implements that were 100,000 to 200,000 years older than H. habilis. So, the start of the Stone Age is a bit debatable.

In terms of social status, most experts agree that the intelligence of H. habilis was more sophisticated than typical Australopithecines or chimpanzees. Yet despite H. habilis's tool usage, they were not the master hunters that their descendants proved to be. H. habilis used tools primarily for scavenging, such as cleaving meat off of carrion, rather than for defense or hunting. There is ample fossil evidence that shows H. habilis was a major staple in the diet of large predatory animals such as Dinofelis, a large predatory cat similar to a leopard. Homo habilis co-existed with many other Homo-like bipedal primates, such as Paranthropus boisei, which was also highly successful-some prospering for many millennia. However, H. habilis, possibly because of its early tool innovation and a less specialized diet, became the precursor of an entire line of new species; whereas Paranthropus boisei and its robust relatives disappeared from the later fossil record.

Homo erectus evolved after H. habilis, about 1.8 million years ago, and used more diverse and sophisticated tools than its predecessors. One theory is that H. erectus first used stone chips of the habilis type and then later developed stone tools flaked on both sides. The double-sided stone tools were used as hand axes from about 1.2 million years ago to about 500,000 years ago. The primary innovation associated with these handaxes is that the stone was chipped on both sides to form two cutting edges. Homo erectus (along with Homo ergaster) was probably the first early human to fit squarely into the category of a hunter and predator and not as prey for larger animals. H. erectus migrated throughout the Great Rift Valley, even up to the Red Sea. This pre-human was learning to master his environment for the first time.

Some dispute that H. erectus was able to control fire. The earliest and least disputed evidence of controlled fire is around 300,000 years old, right at the end of the H. erectus period, and comes from a site which lies on an ancient beach on the French Riviera. There are older Homo erectus sites in France, China, and other areas that seem to indicate controlled use of fire, some dating back 500,000 to 1.5 million years ago. Regardless, it can at least be surmised that the controlled use of fire was not typical of Homo erectus until its decline and the rise of more advanced species of the Homo genus came to the forefront such as, Homo antecessor, H. heidelbergensis and H. neanderthalensis.

Between 400,000 to 250,000 years ago, the trend in cranial expansion and the elaboration of stone tool technologies developed, providing evidence for a transition from H. erectus to H. sapiens, from pre-human to human. The direct evidence suggests that there was a migration of H. erectus out of Africa, then a further speciation of H. sapiens from H. erectus in Africa. This is a hotly debated area in paleoanthropology, but nonetheless, man evolved in Africa.

Numerous scientists and philosophers have speculated about what caused the ultimate development of the modern human with our large brain. Darwin, of course, considered most evolution to be by natural selection which encouraged survival of the fittest. Being fit meant being better able to find food and reproduce the species. It has been shown that a mere 1% difference in reproductive success could result in replacement of one species with another in 30 generations.

Most of the following speculations fall into this 'survival of the fittest" category. Perhaps just one aspect triggered the evolution of our brain or maybe it was a combination of factors. First, primitive pre-humans that successfully made the transition from the rain forest to the savanna grasslands had a brain one-third the size of ours. The various species at this time did not have significant brain growth compared to their rain forest predecessors. As pre-humans expanded into new territories, this demanded adapting to different food supplies and developing new strategies for getting food. A more nomadic life required improved memory of food locations and also identification of food plants and poisonous plants. This information needed to be passed down from generation to generation. Obviously, the ability to expand the food supply would improve the survival ability of the group and consequently result in greater reproduction. Transmitting information from one generation to the next would become of increasing importance. Still, the fact is that pre-humans, with a brain one-third the size of ours, were successful in Africa for thousands of years and their brains evolved little.
What happened next? The Homo group possessed somewhat larger brains than earlier Hominids. The first clear increase in hominid brain size from 400 ml to 700ml occurred about 2 million years ago in H. habilis, the pre-humans that used stone tools. This evolutionarily significant change in brain size cannot be simply accounted for in terms of increased body size alone. Some evidence suggests that these larger brained Homo habilis fed on highly nutritious seafood and fresh-water fishes.

Scientists solved this puzzle of the big brain change by putting together pieces that, at first, looked as if they had no relation. The first piece of the puzzle involved discovering early pre-human populations that demonstrated greater intelligence. They found evidence in the East African Rift Valley and on the southern Cape of South Africa. The second piece of the puzzle was the discovery that docosahexaenoic acid (DHA) was a large contributor to brain growth. The third piece was the discovery that DHA was found in seafood. When scientists put these three pieces together they found that pre-humans who lived near water sources and ate seafood experienced the big brain change! Stone Age men and women collecting shellfish could have easily provided themselves with a plentiful source of brain-specific nutrition, especially omega-3 fatty acids, and their children would have naturally participated in the exploitation of this extremely rich resource of nutrition. There must have been enough omega-3 and omega-6 fatty acids available in their diet to provide many generations with fuel for fetal/infant development as well as childhood and adult needs for the cardiovascular system and the brain.

In contrast, the inland Australopithecines did not have access to omega-3 fatty acids and for three million years got stuck at a brain capacity that was not much bigger than a chimpanzee's. They don't show much evidence of advanced tools either. I really see this seafood connection as a major player in what got the brain evolving. But then what happens next in the brain's development? Well, pre-humans most likely lived in groups. The availability of food and the nomadic life would have likely determined the size of the group. If the group was small, it could be family-based with possibly a dozen individuals. Multiple family groups would likely become tribal and have a leader. Most modern apes live in a tribal-like group with a leader. It is likely that most pre-humans lived in similar tribal-like groups.

Remember that the essence of Darwinian evolution is competition or "survival of the fittest". So, what would be some of the elements of competition in a tribal-like group that would improve the survival of pre-humans? Good. Food would be the primary concern of pre-humans, as it is for all animals. Protection against predators is also extremely important, particularly in Africa with its abundance of large predators. Shelter is important, particularly for the female and her babies. And, of course, mating and reproduction are critical for the species to survive and carry on genes that enhance its survival. Certainly, all of these elements are important for pre-humans, but do they contribute to expanding brain size? Let us imagine a primitive tribal situation with Homo erectus, our first human-like ancestor. Language did not exist. Tools were very primitive. Campfires had not been developed, but possibly were later during the time of H. erectus. Provisioning the tribe was critical. And the men probably scavenged for meat, while the women may have collected edible plants and roots.

As the group became larger, it became necessary for some kind of organization to develop. As with other apes, early human males began to compete to control the group. Why? Well, with more control, the male had more access to food supplies. Since dominant males had control of the food supply, females were likely to be attracted to them. In order to be in control, the leader would need to be not only stronger than the other males, but also smarter for survival of himself and the tribe.

The size of the group may have been important. Studies of hominids and monkeys suggest that brain size is related to the size of the group-with individuals in larger groups having larger brains. Another spark. The theory is that social interaction in a larger group is much more demanding than in smaller groups. No wonder we're going crazy with our population so large!

So, with this situation, strong, smart males in control of the food supply would be highly attractive to females. Competition among females for the favors of the males with the best food supply could select for increasing intelligence. The female that obtained a higher protein diet would be capable of higher reproduction and improved survival of offspring.

How would women compete for good males?
As the old saying goes "The way to a man's heart is through his stomach." The ability of the woman to provide a good diet for the man would further enhance the selection of females with horticultural skills and cooking skills and would result in better survival for her children. Certainly all of these elements could provide selection pressure for increased intelligence in the females. Another spark.

This increased intelligence enabled these pre-humans to control fire. I would suggest that a major element, not just a spark, in human brain evolution was the acquisition of fire. The brain had already developed substantially, but fire may have enabled further development. Homo erectus had a brain about 74% as large as modern humans or about 800 ml compared to the modern human brain of 1400 ml.

Imagine the tremendous advantage a campfire provided these primitive peoples-increased security at night and a wider range of food resources such as roots and vegetables that required cooking to be edible. Meat also became more palatable when cooked.

Another possible and very significant factor that control of fire could have led to was communication. For the first time they had light in the evening and did not have to go to sleep when it got dark. They could sit around the fire and convey information about the day's hunting or about food resources. Since the women were already developing some communication ability with their children and men had developed hunting signals to aid in group hunting, a synergy of communication could have developed. The people with the best communication skills would have been highly desirable as mates.

Entertainment such as mimicking the sounds of animals of the hunt may have occurred. Reenactment of the hunt may also have been done around the campfire. Also, the children could be put to sleep allowing the men and women to communicate, which was unlikely during the day while the men and women were foraging for food in different locations.

A larger community would allow for task specialization. Yet another spark. Older women could babysit while the mothers foraged for food and prepared food. Older men could specialize in toolmaking. By allowing specialization, tools could improve faster. Communication skills would aid in spreading the improved technology.

Now, in order for the brain to expand, a complex set of genetic modifications would need to take place simultaneously in the female. The fetal skull would have to increase in size to accommodate the larger brain and the female pelvic area would have to change to accommodate the larger head size of the baby. The baby would have to be born in a much more immature condition than pre-humans with their small heads. The increased size of the baby head and the prolonged development of the baby after birth placed major long-term burdens on the mother. Her mobility would become limited and her need for nutrition and support from others would increase.

Consequently, the choice of a mate capable of providing for her needs would be extremely important for her and the baby's survival. Intelligent evaluation of a potential mate would be very desirable in this situation. Since the female's need for support was critical, competition among females for desirable mates was likely intense. The change from a periodic estrus to constant sexual availability may have been a result of this competition. Maybe, significant changes in the female anatomy such as rounded hips, enlarged breasts, and the loss of body hair may have possibly been the result of this competition for reliable mates.

Evolution of the brain probably came in waves. As we can see, the transition from the relatively secure rain forest to the dangerous and difficult grassland environment presented the pre-humans with major challenges. These challenges were met with anatomical modifications such as the foot and the hand. The brain didn't develop much at this point. Then pre-humans began living by bodies of water and eating diets rich in Omega-3 and Omega-6 fatty acids. We see a significant brain development at this point. Then they began using advanced tools and fire and we see further growth of the skull and a change in the size of the female pelvis. Communication begins and we see profound changes in the development of the brain.

At some point, the brain develops the ability to ask why and pre-humans, at this point, become human. Story telling, fantasy, religion, and ceremony could have been the last step in the evolution of the human brain. Or perhaps our brains are evolving now.

So what can we conclude from all of this?

The evolutionary story is replete with examples of plants and animals that modify rapidly when placed in a new environment. Many examples are on the Galapagos Islands where Darwin got insight into the process of evolution. The cormorant flew to the islands and then lost the ability to fly since it no longer needed to fly to survive. The spines of the prickly pear cactus on the islands are no longer sharp since nothing feeds on it. The Galapagos lizard learned to swim and eat seaweed. The horse developed teeth adapted to prairie grasses. The expanding grasslands in Africa provided an opportunity for a forest dwelling ape to adapt to a new environment and produced a grassland-dwelling ape capable of efficient walking and running, but it wasn't until all of the social aspects of the pre-humans existence came into play that a radically new type of animal evolved-the brainy human being.

And that changed everything! It was good being social here with you today.