AGAINST the relative calm of the two million years since the Homo genus has been in existence, the helter-skelter of change in culture during the first few thousand years of the Holocene has been astonishing. It tells us that there is something fundamentally different about Homo sapiens from not only any other living creature today, but also from all other members of our genus, from the earliest hominid to the Neanderthals.
Many have thought that this was brought about by changes in the volume of the brain. Palaeontologists once reckoned there was a 鈥渃erebral Rubicon鈥� of 600 cubic centimetres. This, it was thought, distinguished Homo from other primates, but we simply do not understand the significance of brain size for thought and behaviour. Moreover, brain sizes equivalent to those of H. sapiens were reached at least a couple of hundred thousand years before the cultural explosion. Nor, curiously enough, does the emergence of language necessarily explain why our branch of Homo was so successful. Both H. neanderthalensis and H. heidelbergensis evolved vocal tracts that would have been capable of producing a wide range of utterances.
We cannot tell whether these species had the vast lexicon and grammatical complexity that distinguishes language from the vocalisations of apes. But the vocalisations of both were language.
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One use of language by the Neanderthals would have been to pass on knowledge about making stone tools. These were as complex to make as any produced by H. sapiens. Few modern flint-knappers have mastered the Levallois technique, routinely used by the Neanderthals to produce large flakes of a predetermined size and shape. Nevertheless, it is with toolmaking that we begin to find evidence for an enormous cultural gulf between the Neanderthals and H. sapiens.
Neanderthal technology remained largely unchanged for a quarter of a million years. Yet in roughly half that time the technology of H. sapiens has evolved from stone tools to the laptop on which I write this, not to mention the Internet to which it is connected. In fact, our technological evolution did not really get started until after the last ice age had reached its peak, a mere 20,000 years ago.
This phenomenal rate of culture change is the clue that there is something fundamentally different about H. sapiens from all the other members of the human genus. This something must lie within the mind and many would characterise it as symbolic thought 鈥� the capacity to attribute an arbitrary meaning to a sound, movement or an object. The word 鈥渄og鈥� neither looks, sounds nor smells like a dog, for example. Only H. sapiens has left us unambiguous evidence for those practices such as art, ritualised burial and body decoration that imply the presence of symbolic thought. This is Culture with a capital C, entirely different from the toolmaking traditions of chimpanzees. The evidence for symbolism becomes pervasive only about 50,000 years ago, but there are traces of engraved stone and uses of pigments that indicate symbolic thought reaches back to the origins of H. sapiens. It is a distinguishing feature of our species.
But is it enough to describe H. sapiens as the 鈥渟ymbolic species鈥�? Underlying the appearance of symbolic thought there must have been a huge change in human mentality. I characterised this as the change from 鈥渄omain specific鈥� to 鈥渃ognitive fluid鈥� thought.
Domain-specific thought occurs in a mind constituted by multiple intelligences. Each of the domains 鈥� such as those for social interaction, for manipulating objects and for interaction with the natural world 鈥� has a limited connection with the others. Neanderthals could not take what they knew about animal behaviour and combine it with their knowledge about making artefacts to design specialised hunting weapons. They could not design beads and pendants to mediate their social interactions. This would have required bringing together their technological and social intelligences.
All members of Homo 鈥� other than H. sapiens 鈥� had domain-specific mentalities, the most advanced form appearing in the Neanderthals. H. sapiens, however, had the capacity to make mental links. Not only could they combine different types of knowledge, but they also had the capacity to think in metaphor 鈥� a capacity that underlies the whole of science, art and religion. It is the most compelling explanation, I think, for the evolution of the modern mind.
With this extraordinary change in mentality came the ability to create new types of material culture 鈥� artefacts quite different from the tools made by other animals and our hominid ancestors. These were replete with symbolic meanings, whether a painting on a wall or what looks to us today as no more than a mundane stone tool. But material culture was no longer simply a product of the mind: it had become a major shaper of the mind. The cultural environments that we humans create around ourselves are of critical importance to the elaboration 鈥� if not the origin 鈥� of cognitive-fluid thought.
Paintings on cave walls, written texts and mathematical symbols support the complex ideas that are so important to human minds, but which are difficult to grasp, recall and transmit to others, whether they are about religious beings or the nature of quantum mechanics. The earliest modern humans learned what philosopher Daniel Dennett would call a 鈥渃lever trick鈥�: they learned to extend their minds beyond their brains. They escaped from the restrictions that biology imposes upon human thought.
The true impact of this clever trick did not become apparent until more than 100,000 years after H. sapiens had evolved. It is ironic that just as this new, creative type of mind appeared at around 120,000 years ago, the global climate was deteriorating and continued to do so until the height of the last ice age was reached 20,000 years ago. Severe cold and drought decimated human populations, inhibiting the possibility for cultural innovation. Global warming began slowly, and then ended with an astonishing spurt 10,000 years ago. That effectively liberated human thought from its ice-age freezer.
With the new possibilities for colonisation and population growth, and new types of plants and animals to exploit, modern humans really put their creative, cognitively fluid minds into action. Within a few thousand years, communities in western Asia, Mexico, Peru, New Guinea and China had independently invented farming. This demanded a metaphorical mind: thinking of plants and animals as honorary humans that needed to be cared for like children. Farming soon spread into Europe, south Asia and North Africa. It created the economic basis for towns and trade, and led to the first civilisations in Mesopotamia, Egypt and the Indus Valley. Within less than 10,000 years of the first farming, people have walked on the Moon and discovered the structure of DNA.
To understand these achievements we need to appreciate that the modern human mind is far more than the firing of neurons and the swilling of chemicals in the brain. Consider those prehistoric people who painted images of half-human, half-animal beasts on their cave walls in 30,000 BC, and then danced and sung in their presence. These images and performances were not simply products of a mind contained within the skull; they acted to shape the thoughts themselves, thoughts about religious beings that could not have arisen within the brain alone. Painted caves and rituals stored information about the natural and supernatural worlds, supplementing the information that could be stored within the brain and extending the capacity for creative thought.
Now consider someone inscribing a clay tablet with symbols at the Mesopotamian city of Uruk in about 3000 BC, perhaps as a means of recording the movement of traded commodities. And then consider someone else reading the tablet, perhaps after it had reached another city. The invention of writing marked a further means of extending mental capabilities: spoken words, and the thoughts behind those words, could be conveyed across time and space. They helped to formulate the thoughts arising in the brains of people that the scribe has never met. Those clay tablets from ancient Iraq are literally little pieces of ancient minds that were left behind for archaeologists to find.
Finally, consider a far more recent example of a human mind at work: 50 years ago James Watson sat in his room in the Cavendish Laboratory in Cambridge and played with cardboard cut-outs of the structure by fitting together base pairs of DNA. It wasn鈥檛 just his brain that made the discovery; it was also his dextrous fingers and the cardboard cut-outs themselves 鈥� brain, body and material culture are all constituent elements of the modern human mind. They have been so since the appearance of H. sapiens more than 100,000 years ago when a cognitively fluid mentality 鈥� a new type of human nature 鈥� began. This initiated a cultural change that changed gear once the ice age reached its end. It continues to accelerate today.
