EVOLUTION OF THE HUMAN BRAIN

Any of us would be hard pressed to fully realize just how long a time span of six million years actually is. That is the approximate length of time it took for the Homo sapiens brain to develop once our ancestral line diverged from the line which developed into modern chimpanzees and other apes. The narrative of our ancient heritage is a story of challenge, survival, and frequent early death over millions of years of hardship. The fossil record from which we get our data gives hints of only a minute portion of actual biological history and the interpretation of these remains is always open to question and change. Any specific fossil remain cannot reveal how many species existed before and after that particular find. Nonetheless there are discernable patterns that can be explored. One pattern is the frequency of premature death especially of the young and of females who were significantly smaller than the males and also burdened with the care of the young. Individuals who could not cooperate with their peers or made serious mistakes which caused them to be expelled from their groups were not rewarded by huge golden parachute clauses. Most frequently they were slashed and eaten by animals much bigger, much stronger, and much faster than they. The major protection for our predecessors was within the group and cooperation was at a premium. Although it is a fascinating story, it is not a pleasant one and those who assume we have finally arrived at some everlasting plateau of perfection (or even some final adequacy) cannot justify such a whimsical belief by anything that our evolutionary past teaches us of the process. Our futures are still in question just as are all other animal forms on earth and evolution moves on even for us. It is reasonable to recognize that we have been in existence an infinitesimally brief period relative to our ancestors and that we could disappear just as quickly (Fig. 2.1). Several attributes of our ancestors have taken the spotlight as though they were the prime movers in the development of our modern form, divorced from anything social. Considering the ratio of body weight to brain weight, the human brain is the largest in the animal kingdom. However, Richardson (1999: 17) warns that we make too much of this. Until recently, neuroscientists were remarkably vague about