Humans behave differently in many ways to any other species that ever lived, writes Dr William Reville. We are self-conscious, reflective, forward-planning, artistic, musical and religious.
Intuitively one would predict that the evolutionary origin of these characteristics would coincide closely with facilitating anatomical changes. However, we now know that the necessary anatomy was in place for a long time before there was any evidence of modern human behaviour. The story of how we became human is told by Ian Tattersall in Scientific American (December 2001).
Several types of human-like creatures (hominids) existed at one time and modern humans (Homo sapiens) are descended from one of these varieties which when it arose quickly supplanted the other varieties.
The hominids known as Neanderthals became predominant in Europe and Western Asia about 100,000 years ago. Their brains were the same size as modern human brains. They were slightly smaller than modern people but had massive heads with strong jaws and prominent brow ridges on a sloping forehead. They cared for their disabled and buried their dead with ritual. The Neanderthals were replaced throughout Europe about 40,000 years ago by modern humans - Homo sapiens sapiens - called Cro-Magnon Man after the French village where their remains were discovered. The brains of Cro-Magnons were no bigger than those of the Neanderthals, but they put them to new uses.
Cro-Magnons brought with them the full range of modern human behaviours - sculpture, painting, elaborate burial of the dead, ornamentation of utilitarian objects, and so on. They were mighty hunters and in some of their caves they began to draw and paint the animals they hunted: mammoths, horses, wild oxen, bison, rhinoceros and reindeer. They supported some of their fellows as full-time artists. Also, many of their caves were used only for ritual worship. The achievements of the Cro-Magnons stand in stark contrast to those of the Neanderthals or any other hominids. The radically new behaviours of the Cro-Magnons were clearly underpinned by a new capacity to think symbolically. Understanding how this came about is one of the most interesting puzzles in biology.
It would be most convenient if the Cro-Magnons differed sharply in anatomy from preceding hominids in a manner that would explain the origin of the new type of thinking. However, this is not the case. In fact there is evidence of humans who lived as long as 100,000 years ago who are pretty much anatomically identical to the modern human. Modern anatomy considerably predated the arrival of modern behaviour.
Obviously when considering cognitive processes we are talking about the brain. Specialists find it difficult to identify any feature of the Neanderthal brain that suggests a major functional difference between it and the modern brain. In other words, it appears that the brain was physically equipped to support modern human behaviour long before the behaviour appeared.
EVOLUTION does not pre-plan its own journey. Spontaneous genetic changes produce altered structures and natural selection eliminates those structures that are harmful to an organism and favours those that are helpful. If the new structures are neutral in effect, they often remain in place so long as they are not getting in the way. Such neutral developments, or developments chosen by natural selection for a certain purpose, may be pressed into service in the aid of a new function later in the evolutionary history of an organism. For example, feathers were around for a long time before being used for bird flight. They were probably first selected as efficient means of heat insulation.
In the same way, the anatomy of the human brain was not selected because it could support symbol centred cognition, but the selected brain happened to be capable of supporting such cognitive capacity when that cognitive functioning was somehow triggered off later. The world is perceived more or less as a continuum by non-human animals. Symbol centred cognition is that unique human capacity to divide the world into different chunks and to assign symbols to each chunk. One way or another, the human capacity for symbolic thinking is the basis of our creativity, allowing us to mentally shuffle things into different arrangements and to ask "what if" questions.What triggered the development of symbol-centred thinking? This was almost certainly the development of speech. When one human mind communicates with another it does so through words - the coinage of symbolic thinking. Many animals communicate with each other vocally and this communication can be quite subtle. But the only reasoning accessible to animals, in the absence of symbolic thinking, is intuitive reasoning, i.e. reacting to stimulation from the environment in complex ways. Neanderthals undoubtedly communicated vocally with each other but they left little evidence that symbolic activities played an important part in their lives. They probably did not have language as we understand it and thought intuitively. The human vocal tract is the only organ in the animal kingdom (although some birds can mimic speech) that can make the sounds essential for human speech.
This basic anatomical capacity has been present in our ancestral lineage for half a million years, but the ability to speak wasn't realised until about 50,000 years ago. Speech triggered the brain's capacity to support symbolic thinking and this language/ thinking habit spread rapidly through the early modern human world through social interaction. The competitive edge supplied by the language/thinking ability was so sharp that it allowed the hominid strain who acquired it to crowd out all competing hominids and to inherit the earth.
Dr William Reville is a senior lecturer in biochemistry and director of microscopy at UCC.