Brain

   1) Biological and Social Brain Development

   Among the higher mammals the great development of neocortex occurs.

   In each group of mammals there is a steady increase in the area of the association cortex from the most primitive to the evolutionarily most recent type; there is an increase in the number of neurons and their connections. The degree of consciousness of an organism is some function of neuronal cell number and connectivity, perhaps of neurons of a particular type in association cortex regions. This function is of a threshold type such that there is a significant quantitative break with the emergence of humans. Although the importance of language and the argument that it is genetically specified and unique to humans must be reconsidered in the light of the recent evidence as to the possibility of teaching chimpanzees, if not to speak, then to manipulate symbolic words and phrases, there are a number of unique human features which combine to make the transition not merely quantitative, but also qualitative. In particular these include the social, productive nature of human existence, and the range and extent of the human capacity to communicate. These features have made human history not so much one of biological but of social evolution, of continuous cultural transformation. (Rose, 1976, pp. 180-181)

   2) Distinctive Evolutionary Properties of the Brain

   [S]ome particular property of higher primate and cetacean brains did not evolve until recently. But what was that property? I can suggest at least four possibilities . . . : (1) Never before was there a brain so massive; (2) Never before was there a brain with so large a ratio of brain to body mass; (3) Never before was there a brain with certain functional units (large frontal and temporal lobes, for example); (4) Never before was there a brain with so many neural connections or synapses. . . . Explanations 1, 2 and 4 argue that a quantitative change produced a qualitative change. It does not seem to me that a crisp choice among these four alternatives can be made at the present time, and I suspect that the truth will actually embrace most or all of these possibilities. (Sagan, 1978, pp. 107-109)

   3) The Evolutionary Increase in the Size of the Main Areas of the Brain

   The crucial change in the human brain in this million years or so has not been so much the increase in size by a factor of three, but the concentration of that increase in three or four main areas. The visual area has increased considerably, and, compared with the chimpanzee, the actual density of human brain cells is at least 50 percent greater. A second increase has taken place in the area of manipulation of the hand, which is natural since we are much more hand-driven animals than monkeys and apes. Another main increase has taken place in the temporal lobe, in which visual memory, integration, and speech all lie fairly close together. And the fourth great increase has taken place in the frontal lobes. Their function is extremely difficult to understand . . . ; but it is clear that they're largely responsible for the ability to initiate a task, to be attentive while it is being done, and to persevere with it. (Bronowski, 1978, pp. 23-24)

   4) The Human Brain and Ethical Principles

   The human brain works however it works. Wishing for it to work in some way as a shortcut to justifying some ethical principle undermines both the science and the ethics (for what happens to the principle if the scientific facts turn out to go the other way?). (Pinker, 1994, p. 427)