Does Darwinian theory still affect and control our modern human lives? Are we still undergoing the slow process of natural selection? Or is there a different paradigm in place now that we are more in control of our own destiny?
By Ian Tattersall
With our big brains, tiny faces, and a bizarre upright form of locomotion, we human beings are rather peculiar creatures. So perhaps it’s not surprising that paleoanthropology – the science that studies human evolution and how we got to be the way we are – should have a rather peculiar history. The scientists who seek to understand the evolution of virtually all other living organisms are immediately confronted by natural diversity: the fact that successful groups – rodents, for example, or whales – tend to throw off many different species, each one exploring in its own way the potential inherent in being that kind of creature. The resulting genealogies are typically extremely bushy, with numerous branchings and dead ends. So the key question that most paleontologists must answer, right off the bat, is how and when and why that diversity was generated.
Paleoanthropologists, on the other hand, study a single species – Homo sapiens – that is the sole representative of its group alive in the world. Judging from our situation today, biological diversity is not a factor in the human story; and as a result, paleoanthropologists have tended to reconstruct the past of our lonely species by simply projecting it back into the past, in a straight line. Back into the mists of time, a long succession of ancestors gets steadily more primitive and less like us, until it ultimately melds with the lineage that led to our closest living relatives, the African great apes.
This atypical perspective has hugely influenced our view of the past of our species and of how we became what we are. And it explains the spirit of “human exceptionalism” that has so deeply pervaded paleoanthropology. What’s more, without understanding the contorted history of paleoanthropology, it is often difficult to understand the many different interpretations of the same phenomena that are current in this famously disputatious science.
In a recent book, Masters of the Planet: The Search for Our Human Origins, I tried to provide a coherent explanation of how a bipedal but otherwise unremarkable ape, living some seven or eight million years ago, contrived in that relatively short period of time to become the remarkable phenomenon that Homo sapiens is today. And I discovered that to maintain coherence I had to leave out almost any references to history. Yet this omission left the story curiously unfinished, and I felt compelled to complete it with my latest book, The Strange Case of the Rickety Cossack, and Other Cautionary Tales From Human Evolution.
In the Rickety Cossack (its title refers to a pre-evolutionary attempt to explain the peculiar anatomy of the newly-discovered Neanderthal fossil from Germany), I explore how, in the century and a half since Charles Darwin published On the Origin of Species, the science of paleoanthropology has diverged in outlook from other areas of paleontology. It is crucial to understand the tortuous history involved because it impacts directly on our ideas about the kind of creature we have become. For example, the narrative that describes us as gradually modified over vast spans of time strongly implies that we have somehow been perfected over the eons by natural selection.
Natural selection is, of course, the unconscious force of nature that Darwin told us lies behind the enormous changes in the makeup of life on Earth that have occurred over the last four billion years. It is an incredibly simple idea, and seems self-evident: in any generation, some members of any population will have more offspring than others. These are the individuals that are best adapted to their circumstances, and their progeny will share their favorable features. Over time, this mindless force will shift the entire population toward better adaptation.
A great story; but, as with most such stories, the reality turns out to have been a bit more complicated. Environments turn out to have changed more rapidly and frequently in the past than natural selection could possibly track, and selection itself has proven to be more of a stabilizing influence – trimming off the extremes of variation in every generation – than a force for change. Most of the time, its major function is keeping the whole population as viable as possible. Evolutionary change is more closely associated with environmental fluctuations, and with spontaneous genetic modifications that are basically random with respect to adaptation.
The known human fossil record has expanded hugely since the linear view of human evolution was initially developed. And its enlargement has clearly shown that the history of the human family, far from being an exception, was in fact pretty typical for a successful mammal family. Our biological history has also involved experimentation with the potential inherent in belonging to our family; and typically there have been several kinds of hominid around in the world at any one time. In fact, as recently as forty thousand years ago, Homo sapiens shared the Earth with at least four other hominid species. It is actually a highly unusual situation for us to be the only kind of hominid around on the planet. Which surely says much more about our own rather special nature than it does about the broader zoological family we belong to. We are clearly not only intolerant of competition, but within our group we have a unique ability to enforce that intolerance.
So what happened? What made that difference, and how did it arise?
The key seems to lie in the entirely unique way in which modern human beings process information. We deconstruct both our surroundings and our interior experiences into a vocabulary of mental symbols, which we can shuffle around in an organized manner to make statements not only about our mental states and the world as they are, but as they might be. This symbolic cognitive style of ours has hugely magnified our planning abilities, to a degree with which no other species can compete. And a look at our fossil and archaeological records suggests that these abilities are completely unprecedented. They seem to have been entirely unanticipated even by our closest extinct relatives, complex cognitively as those other hominids evidently were.
The two and a half million years ago since the first simple stone tools were made have seen sporadic technological advances, from the first simple sharp stone flakes all the way up to carefully-shaped points hafted on to wooden spear shafts. But although our predecessors were clearly crafty and resourceful, only amazingly recently – indeed, only well after the first anatomically-recognizable Homo sapiens had appeared in Africa some 200,000 years ago, do we find the first intimations of symbolic behaviors. At around 100,000 years ago, evidence of bodily decoration appears in Africa, closely followed by the manufacture of objects bearing geometric engravings that clearly encoded meaning. By about 40,000 years ago, fully-formed modern human sensibilities are witnessed by the powerful cave art of Ice Age Europe; and now we are sending probes to Pluto and beyond.
What seems to have happened is that, by the time the anatomically distinctive Homo sapiens came into existence, the human brain had evolved to a point at which a small genetic change could produce a brain capable of symbolic thinking. Once that biological innovation had been acquired, by a species that at the beginning was still behaving much as its predecessors had, a cultural stimulus was needed to kickstart the new cognitive capacity it made possible. Most likely, this cultural stimulus was the invention of language – the ultimate symbolic behavior – in a small African community at some time around the 100,000-year point. By around 70,000 years ago the descendants of that population were already moving out of Africa; and in an amazingly short time they had taken over the entire world.
Whatever the exact details of this process may have been, the acquisition of modern human cognition was clearly incredibly recent. It took place very rapidly indeed, within the tenure of our own species. And what is more, it was entirely unanticipated in the archaeological record. This geometry of events is important, because it is fashionable nowadays to argue that, when we behave oddly, we do so because we are still behaviorally adapted to an Ice Age environment that is no longer relevant to our modern circumstances. The implication is that we will have to wait – a very long time – for natural selection to catch up.
But the reality is very different. On the short timetable involved, there is no way in which our amazing cognitive style could have been slowly molded over the eons by natural selection. Our mental capacities are emergent, built on many millions of years of essential evolutionary acquisitions, but not predicted by them. In other words, we are not the perfected product of a gradual process. This in turn helps explain the paradoxical nature of the human condition which, despite the philosophers’ and psychologists’ best efforts, still resists characterization. And, cheeringly, it means that individually we human beings are not condemned by our biology to be the kind of creatures we are. We really do have free will.