What Made Us Human?

M.K. O 'Brian

Anthropology is in a constant sate of flux, any chronological interpretations based on the fossil record are subject to amendment as new finds come to light. Theories are formed, adapted and abandoned. One factor that has remained constant is the belief that geological upheaval and climatic change provided a catalyst for the evolution of modern mammals, including our ancestors. Apart from the changes in environment resulting from climatic fluctuation, another factor in the cause of speciation is geographical separation, in our own extreme case, involving more than simply trading toes for hooves and eating grass instead of leaves, in all probability, a more concentrated, localised separation involving a small part of the wider population. This kind of isolation event was possibly repeated several times, up until the emergence of anatomically modern humans.

A four million year gap appears in the fossil record, covering one of the most important phases in our evolution, during which our last completely ape-like ancestors became hominids, or proto-humans. This dearth of evidence could be the result of a particularly arid phase, moisture being necessary for the preservation of fossils. Before the practice of ritual burial became established, well preserved fossils are rare finds.

Despite the lack of a definitive, so-called "missing link", the study of genetics has proven beyond a doubt our affinity with the apes and the rest of the Animal Kingdom. Darwin was right and we are quite literally just animals, albeit more clever than most. I say most because when it comes to higher order mammals, like the dolphin family, any comparison of our intelligence with theirs is impossible to quantify. The main difference between us and them is that dolphins have become perfectly evolved to thrive in their natural environment; so much so, that the evolutionary pressures that plagued their land-living and amphibious ancestors no longer apply, leaving no need for them to drastically evolve further. In contrast we are far from perfectly adapted to survive in our natural environment, it could even be said that we are decidedly maladapted, and that our ancestors survived at all is nothing short of a miracle. Modern humans are the only members of the hominid branch to have become successful, all our relatives having lived a constantly precarious existence. How we became successful and overcame the environment we were maladapted to thrive in was through adaptive generalisation rather than specialisation, along with the development of culture and ultimately, civilization.

From what we understand of the evolutionary process and the rates of positive mutation driving it, the process seems to idle along very slowly for most of the time, concerning itself with combating disease and bringing about more subtle physical variations in response to climatic conditions. Occasionally, various factors contribute towards producing an acceleration of the process, a population bottleneck presents a species with the choice of perishing or evolving. In other words, the only drastic evolution that has occurred in human history seems to have been when we were on the brink of extinction.

For the complexity of life on Earth to have come about simply through positive mutation seems a mathematical impossibility. Knowing what we do about the rates of mutation there just wouldn’t have been enough time. Scientists can talk about monkeys banging away on typewriters until they eventually, and coincidentally, come up with the works of Shakespeare, but the objective truth is that no one knows exactly how the evolutionary process works. All we know for certain is that we did evolve. The outdated but still prevalent Mechanistic approach to understanding our condition has failed in providing the "theory of everything it" promised. If we accept the limitations of logical inquiry, it is only reasonable to suspect some "vital" motivating factor in the evolutionary process, and there is no evidence to prove otherwise. This doesn't mean that we should stop trying to understand as much as is "humanly" possible.

People often pose the question are we still evolving? Although, as with most aspects of human evolution, not everyone agrees, it seems reasonably safe to subscribe to the opinions of men like Jacques Monod, Stephen Jay Gould and Steve Jones, so far as, since human culture became well established around 40,000 years ago, natural selection no longer affects us in the way it did our ancestors, although it could be argued that the advances of the last 10,000 years constitutes an example of evolutionary acceleration in itself. Perhaps the simple answer is, of course we are still evolving, the process may have an idle mode but it cannot be stopped completely, therefore, the only variation is in the fluctuations of speed at which we evolve.

Studies by evolutionary geneticists, led by Jianzhi Zhang at the University of Michigan, show that over the six or so million years since humans and chimps split from our common ancestor, more mutations have occurred in chimps – 233 compared to our 154. Presumably, we would expect that over the several million years following the split, humans would have been subject to a higher rate of mutation due to our more drastic evolution, and the fact that, initially, hominid populations would have been much smaller than those of chimps, leaving us more prone to the alteration of proteins, which leads to mutation, but the eventual increase in population and stabilization of our situation led to the statistical reverse. Now that we have adapted to thrive in our environment, further drastic adaptation is no longer required, for the time being. At least, not physically.

A species is literally defined by its chromosomes, their number, but more importantly, their order and banding patterns. All modern humans are capable of interbreeding; therefore, as no genetic drift has occurred, we all belong to a single species. Among other animals, we often find that such drift has occurred between populations showing no more physical variation than we do, leading to the classification of a subspecies. The rule "seems" to be that, while procreation is guaranteed between fertile members of separate groups, full speciation cannot be said to have taken place.

Evidence of hominid dental characteristics can be found stretching back over 40 million years to the Fayum region of Egypt. The geography of the world was much different then, the relatively flat landscape and humid climate, prevalent away from the poles, proving ideal for the spread of forested habitats and arboreal species like primates. Somewhere around 25 million years ago, monkeys and apes split from a common ancestor leading to a period where apes became the dominant primates. This period is often referred to as the "Age of Apes". The virtually unbroken belts of rain forest, stretching across the Old World, allowed for an exchange of fauna between Africa and Eurasia, cats spreading out of Asia, and Apes out of Africa. Towards the end of this Simian Age, the ancestors of orang-utans took advantage of such conditions to colonize Asia, becoming the first of the Great Apes to split from the common stock, somewhere around 13 million years ago. The ancestors of gorillas split, perhaps, a few million years later leaving us with the last common ancestor of common chimps, bonobos and hominids. It should be added that there is some debate about whether the gorilla-chimp split occurred before or after the hominid divergence.

This halcyon period for apes came to an end as the result of geological upheavals caused by tectonic activity. As continental plates collided, the forming of the worlds great mountain ranges brought about changes in climate and habitat. As regards the main theatre of hominid evolution in East Africa, the formation of the Great Rift Valley had an immense impact on the environment, to the east of the highlands a rain shadow area formed and the resulting decrease in annual rainfall led to the spread of savannah type habitats at the expense of lowland rainforest. The modern mammals we are familiar with today adapted in response to these changes. In the past, interpretations of these facts led to an over emphasis of the "savannah factor" in explaining how the evolution of hominids came about. The general consensus of opinion today is that such extreme conditions did not apply until around 2 million years ago, the same time that large 'habilis' type hominids appear.

Returning to the last common ancestor of chimps and hominids, let us consider what such a creature may have looked like.

"Shape differences between taxa suggest that the 'Pan-Homo' ancestor was phenetically in the range of modern great apes and more similar to gorillas than to chimpanzees. In other words, the common ancestor that is reconstructed by linear parsimony falls nearest to gorillas, suggesting that Pan is autapomorphic in many respects. This condition is consistent with qualitative observations on fossil hominin temporal bones."

Lockwood, Kimble and Lynch. Edited by Pilbeam

Although this common ancestor would have appeared far more ape-like than human-like, in comparison to modern apes it would have appeared much more hominid-like, being far less specialised and, in contrast to the knuckle-walking apes of today, less awkward in its movement. In clinging to an arboreal lifestyle the great apes, in a sense, devolved, developing large canines for defence and abandoning the dental characteristics that helped define the hominid branch. This consideration has made scientists in the past make statements like "We are not descended from the apes, they have devolved from us". Although this may seem rather pedantic, it puts some perspective on the old idea that chimps became human. Still, all apes have the potential, given the right conditions and sufficient time, to become hominids.

So, somewhere around 8 million years ago, following the proposed gorilla split, we have the last common ancestor living in the region of North East Africa. Although the forests are not yet disappearing, mammals are adapting to more open environments. For most this adaptation will be finalised by 3-2 MYBP, but in our case, not until around several hundred thousand years ago. The question for the moment is how did the speciation leading to the Pan-Homo split come about? Of course, we can only speculate, but some factors must be assumed. There was a geographical separation of a small portion of the wider population, namely, the hominid ancestor. This group, being vulnerable to mutation, became a separate species. In the meantime, ancestral chimps began following their own evolutionary course, retreating with the shrinking forests and becoming more specialised.

As all apes possess 24 pairs of chromosomes compared to our 23, it seems most likely that we are the odd one out; otherwise, all the other apes would have had chromosomes split in two to account for the difference. This explanation seems less probable. Much simpler and more logical is that two shorter chromosomes fused together in hominids to form chromosome Number 2. If #2 is lined up with the pair of chimp chromosomes that match it, ours seem to have attached head to head, the evidence is in the tails. Further evidence is supplied by the study of repetitive DNA called telomeres, chromosome caps which prevent DNA from unravelling; telomeric DNA possesses a specific sequence. The centre of #2 has DNA with the telomeric signature on both sides of the centomere, the pinched portion of the chromosome. This only makes sense if fusion occurred. All this is basically what differentiates us genetically from other apes. By implication, the conditions that gave rise to this must have been unique in comparison to the speciation between our relatives.

Each ape species has two chromosomes unrelated to those of the others (#4 & 17); this represents much of the uniqueness of each species.

Those descended from the last common ancestor, common chimps, bonobos and humans, share similarities in the Y chromosome not shared with other apes (chromosome-1-derived fragment), indicating our closer affinity.

"Thus, this shared derived (synapomorphic) trait provides clear evidence for a Homo-Pan clade independent of DNA sequence analysis."

Wimmer R, Kirsch S, Rappold GA, Schempp W.

It must be admitted that, by its own self-imposed strict discipline, science cannot, as yet, fully explain exactly how and why this all came about, some details are missing. However, the broad overview remains one of exceptional clarity. Any manipulation of the holes existing in scientific explanations to argue non-descent from apes, like blind faith itself, requires extreme self-delusion. The argument against speciation, that the first individual in a group to undergo speciation would be incapable of producing fertile offspring with the rest, is not supported by observations regarding the subspecies of other mammals. Nature allows for some overlap, so that although successful interbreeding may not be always guaranteed, it is possible. The example of mules is an exception, not the rule.

Whatever happened to the isolated group that split from the common ancestor, it led to the appearance of the smaller australopithecine type of early hominid, arguably, nothing more than an ape that developed bipedalism, but representing the transitional phase leading to the larger true hominids, like 'habilis'.

Here it seems reasonable enough to postulate a repetition of the isolation event that may have caused the split from the last common ancestor, such as has been suggested by Hawks and Wolpoff, also accounting for the co-existence of several hominid types in East Africa for over a million years. However, the so called "big bang theory of human evolution", which followed publication of the research, brings to mind some kind of lycanthropic metamorphosis. The evolutionary process may have an accelerator but it's no Maserati.

Many people who try to imagine a speeded-up version of our evolution find the ape-to-human transformation beyond their imagination. A good aid to overcoming this stumbling block is the process of Neotony, the retention of juvenile characteristics into adulthood. Although far too simplistic as an explanation of our overall evolution, it will serve well in the context used here. The infants of apes trigger off our sense of empathy even more than puppies; this is because they remind us of our own young - much more so than their parents remind us of us – much sparser hair, the lack of developed brow ridges and symmetrical faces in comparison with the adults. As the infant grows, these juvenile characteristics are lost, but imagine if it retained them, just becoming larger. Then its own offspring remind us even more of ours, and so on. Imagine this process taking place over the better part of six million years and you have a modern human.

Other issues that fascinate people pertain to the interaction between those different hominids who shared time and space, especially the implications for interbreeding. Evidence relating to this question comes not so much from the study of primatology but observations of mammalian subspecies in general.

Tigers and lions are basically the same thing and are generally regarded as a sister species, though it could be reasonably argued that lions merely represent a subspecies. The panther family has its origins in the rain forests of Asia. With the exception of the Siberian branch, tigers clung to the jungle environment while lions adapted to the savannah, possibly to exploit a niche left vacant by the decline of the sabre-toothed cats. Like most cats, both have 36 chromosomes, but genetic drift has occurred as a result of geographical separation. This also led to a departure in mutual behaviour. In captivity, interbreeding is possible, but not always guaranteed. Exactly how long they have been geographically separated is uncertain, but it must be reasonable to assume that at some points during that time, their range has overlapped. On such occasions as the big cats encountered one another, they must have both recognised their similarities and differences, yet even apart from their territorial nature, interbreeding would have been almost impossible, due to their being completely different social animals, lacking the social skills necessary to interact with each other on the same level. Such differences in behaviour form in themselves a barrier to interbreeding. The wolf and coyote are even more similar genetically, their differences being simply in size and behaviour resulting from the exploitation of a different niche. Under normal conditions wolves drive off or even kill coyotes for competing over some of the same resources, however, when wolves find themselves in decline due to human persecution, the males have no problem seeking out coyote females for mating. Desperation overrules normal convention in the urge to pass on genes, albeit unconsciously, as Richard Dawkins would assert.

Even australopithecines such as 'africanus' and 'bosei' - which were simply gracile and robust versions of the same thing - would have been influenced by some aspects of these considerations, despite not being carnivores and, no doubt, often gathering food peacefully, side by side. Such considerations would have made interbreeding between early modern and archaic humans unlikely, though not impossible.

Perhaps the next major milestone in our evolution occurred around two million years ago, when 'Homo habilis' became "the handy man". Tool-making coincides with the earliest evidence for the evolution of the Broca's area of the brain, associated with speech, associated with speech (Holloway).

The further enlargement of the human brain was made possible by the powerful cooling system which allows us to lose heat through perspiration; lacking such a system limits the brain size in other land mammals.

According to genetic studies, led by David Reed,at Florida University, the key to understanding our nakedness in comparison to other apes lies with lice. Humans are the only primates to be plagued by three types of lice: head lice are ancestral and diverged genetically from our relative's around 6 million years ago, pubic or crab lice seem to have passed over from gorillas, around 3 Million years ago - presumably, this was when hominids began to lose body hair, a trend in progress since austrlopithecines appeared.

The clothes louse diverged around 650,000 years ago, perhaps providing an indication of when we became almost truly hairless, sweaty, and allowing for our brains to become four times the size of an australopithecine's.

So 'habilis' thrived while the australopithecines became extinct. Despite their small brains, these early humans must have been experiencing some kind of conscious shift differentiating them from other apes. One million years ago, for the first time since the "Age of Apes", one of our ancestors managed to leave Africa and colonize other areas of the Old World. And yet, it would only be those hominids remaining in Africa who would survive and become anatomically modern humans.

The last isolation event occurring to date, brought about the population bottleneck of several hundred thousand years ago in the region of East Africa. At that time, possibly due to an extremely dry period, archaic human populations (which then included our own ancestors) were in decline across the Old World. Most of those populations would never recover, with the obvious exception of our direct ancestors, who eventually established themselves along the south-east coast. That we are all descended from that small group of survivors is implied from the study of genetics. Becoming anatomically modern made us far more adaptable than our predecessors and relatives, leading to our colonization of the globe.

Of course, anatomy is not all that being 'Homo sapiens sapiens' is about. We have to take into account the development of higher consciousness, but then, our cerebral enhancement probably predated physical modernity and was not exclusive to our direct ancestors. It is a huge presumption to claim that, just because our ancestors were more efficient at tool-making and killing, they must have been essentially more intelligent than say, the Neanderthals of Shanidar – which seems highly unlikely. Otherwise, craftsmen and soldiers would make better academics than scientists. Having said this, at that point in the race, early modern humans obviously had some practical advantages over the rest.

Something that seems obvious, yet is seldom stated, is that as all apes had the potential to become hominids, all archaic humans had the potential to become anatomically modern, given enough time. It seems clear from the study of fossil skulls that such a process was taking place, but for all but our own direct ancestors, time was running out. The fact that we succeeded was not because we were inherently superior to the others, but simply because we were in the right place at the right time. It appears that, up until physical modernity had been achieved, Africa, the matrix of human evolution, was the only place to be.

Another question that fascinates the general public is – what would our earliest modern ancestors have looked like before racial variation developed? Fossilized remains cannot shed much light on this, but people still exist who have adapted to the same type of African environment our ancestors emerged from. Up until fairly recently in history, the South African Bushmen inhabited a far wider area covering most of eastern Africa. The Bushmen possess some unique physiological characteristics: the men have a permanently semi-erect penis and the women's labia forms an external flap, adaptations to living naked in the bus; they are also steatopygic, having the ability to store fat in the buttocks and thighs in case of hard times. There is no implication that Bushmen are in any way primitive, rather, they occupy a special position in the human race - as would have their Hottentot kin, if we hadn’t wiped them out. If all the dogs in the world were allowed to breed indiscriminately, the result would be wolves. Inevitably, through inter-racial pairing, the human race is destined to resemble its earliest modern ancestor once more. One day we will all look something like Bushmen, or perhaps more accurately, Hottentots.

As for the more distant future (if we do manage to survive the political mismanagement we are subjected to), advances in technology will no doubt nullify the need for size and strength. This enhancement of our ability to be physically lazy will lead to an economical reduction in stature - a factor that will impact in particularly on our descendents who live in extraterrestrial, artificially supported environments. Accordingly, sexual dimorphism should no longer be genetically or psychologically relevant, particularly if we abandon testosterone-fuelled aggression. Not only will non-sexual, physical differentiation between the genders disappear, but, following the necessary attitude adjustment regarding the prejudice that has always prevented women from contributing towards the advancement of civilization, true sexual equilibrium should be achieved. The people of the future will probably come to look something like the Baka (pygmy) people of West Africa.

I must mention the speculative hypothesis put forward by Sir Alistair Hardy, the one that has caused some mild controversy. Like no other theory it postulated the kind of isolation event necessary to bring about the evolutionary acceleration probably required for such a drastic adaptation as ours. I must admit the possibility that I tend to exaggerate the need for such extreme conditions, and that our evolution may have taken place over a long enough period of time for it to have been a gradual process inevitably leading to the emergence of modern people. I'm no expert, but then, when it comes to the human condition, is there any such thing as an expert? As for the Aquatic Ape Theory, even if an aquatic phase did not act as a major catalyst in our evolution, the probability remains that aquatic environments, from time to time, provided some more subtle, less discernible contribution towards our evolution.

If there had actually been any merit in many of the accepted speculations that have dominated anthropology since its conception, we wouldn't be able to discuss our evolution; we'd simply be a misogynistic ape version of baboons. Don't even go there ladies.