Deepak Lal: 'Human' uniqueness?

Humanly modified environments are more congenial to us than to predators and parasites, and we can stay ahead by cultural adaptations.

Walking across the UCLA campus, my wife recently came across a bloody glove on a spade with a sign: "Salad is Murder". This anthropomorphising of Nature might appear to be part of growing New Age sensibilities in the West, but it poses a question which has exercised human minds for millennia: What is it to be human? This is the subject of a fascinating book by the historian Felipe Fernandez-Armesto (Humankind""A Brief History). Having lived within the animal kingdom since the Stone Age, he argues, the earliest humans recognised their kinship at least with the great apes and saw themselves as part of Nature. It was in the first millennium BC in the Axial Age when the great sages in India, China, the Near East and Greece created the world's major "religions" or cosmologies that humankind came to place itself above Nature, claiming at least trusteeship, if not dominion, over it. The Upanishads were the first to put humankind above the other animals because of their powers of reasoning and, above all, because of the claim that they alone had an eternal and immutable soul. But this still raised the question whether humans had the freedom to exploit other creatures for our benefit, or, being the stewards of Nature, we had an obligation of care for the whole of creation. For, as Mahavira argued, though different, the souls of animals most closely resembled those of humans and had therefore to be treated with respect.

But as greater knowledge of our closest cousins""the great apes""developed (particularly the "orang-utans", which in Malay means "man of the woods"), it became difficult to draw a sharp distinction about the uniqueness of the human ape. These close cousins were described as degenerate humans. From this, it was a small step to describe the "savage" primitive tribes like the pygmies of the Congo in similar terms, as degenerate "races", and the seeds of racism were sown. The Darwinian revolution showed that instead of apes being degenerate humans, humankind were just evolved apes, whilst modern genetics has established that there are no races, as there is barely any genetic difference between the most widely separated humans. Moreover, the genetic difference with our closest cousins, the chimpanzee, is also small.

So the next avenue explored to define the uniqueness of the human animal was cultural. But as the study of the variety of human cultures progressed with the Voyages of Discovery, their sheer diversity made any universal features hard to identify. More seriously, our closest hominid cousins seemed to share many of the elements of "culture" which had seemed to be uniquely human. The key example is the Neanderthals. They had bigger brains than humans and similar forms of culture. They probably also had language. Thus, they engaged in ritual burials, which shows that they had the two ideas of life and death, and in these burial rituals shared the common culture of humans, who, apart from a merely instinctive valuing of life, have "a conviction that life is worthy of reverence [and], which has remained the basis of all human moral action ever since". But the Neanderthals became extinct and Homo Sapiens have multiplied and colonised the globe.

So what explains this dominance of Man, which is an empirical vindication of his uniqueness? A recent book by my UCLA colleague Robert Boyd and his long-time collaborator Peter Richerson (Not By Genes Alone""How Culture Transformed Human Evolution), which could well prove to be as important as Darwin's "Origin of the Species", provides a Darwinian account of the evolution of human culture and the biological basis for its uniqueness. It is what distinguishes us from our cousins in the animal world.

They argue that from the archaeological and fossil record, modern humans evolved over about 160,000 years and spread across the world 50,000 years ago. Humans, with their flexible brains, evolved in the Pleistocene. Fig. 1 shows the picture of climate deterioration, which paleo-climatologists have recently constructed, for the last 3 million years. During the last Ice Age, in the Pleistocene, the variability of climate increased markedly. The data from the Greenland ice core in Fig. 2 show this intense climatic variability when the human animal was evolving through Darwinian natural selection. Boyd and Richerson argue that, to deal with the high variability of the climate, the human animal developed a brain that provided the psychological machinery capable of the cumulative cultural change, which is unique to humans. This cultural evolution allowed social learning, which was transmitted to offspring to cope with the fluctuating environment. Unlike the other apes, human social learning consists both of imitation and learning de novo. This leads to cumulative cultural adaptations in a form of cultural evolution, which is more rapid than the genetic evolution and limited social learning based on imitation that most other animals have to rely on to cope with a changing environment.

The increasing variability of the Pleistocene climate also led to increases in brain sizes of other mammals, but the size of the human brain began to diverge from other mammals and it was these more complex brains that allowed the social learning, which allows a flexible response to novel environments. This behavioural flexibility also favoured a longer childhood to allow enough time to learn, and a longer life span, which allows humans to get more benefits from what they learned during their long costly childhood.

The relatively stable climate during the last 11,000 years has not led the flexible human brain to regress to its pre-Pleistocene form, because cumulative cultural change has led to rapid environmental changes introduced by humans""like agriculture. These humanly modified environments are more congenial to us than to our competing predators and parasites, and we can stay one step ahead of them by cultural adaptations. Because, in the arms race between us and other species that have to rely on slow-moving genetic evolution, we have won by faster counter-adaptations based on the much faster cultural evolution. There does, therefore, now seem to be the beginnings of a general theory that is linking biology, archaeology, anthropology and the neuro-sciences, which will provide a scientific explanation for the uniqueness of the human animal and its astounding ascendancy.