Warm-blooded vertebrates

Usage examples of mammals.

The fetus may have characteristics, like the gill slits in mammals, that are entirely maladaptive after birth, but as long as they cause no serious problems for the fetus and are lost before birth, they can be retained.

In non-primate mammals and in reptiles, comparable ritualized behavior seems to be controlled in the same part of the brain, and lesions in this reptilian component can impair other automatic types of behavior besides ritual-for example, walking or running.

And indeed in human intrauterine development we run through stages very much like fish, reptiles and nonprimate mammals before we become recognizably human.

The brains of mammals are ten to one hundred times more massive than the brains of contemporary reptiles of comparable size.

It is possible that lower mammals and reptiles, lacking extensive frontal lobes, also lack this sense, real or illusory, of individuality and free will, which is so characteristically human and which may first have been experienced dimly by Proconsul.

For human beings, and indeed for all mammals, it is the other way around.

The amount shown for mammals is less than for human beings, because most mammals have less genetic information than human beings do.

For a given body mass or weight, mammals have consistently higher brain mass.

Since we are mammals, we probably have some prejudices about the relative intelligence of mammals and reptiles.

The two subsequent bursts of brain evolution, accompanying the emergence of mammals and the advent of manlike primates, were still more important advances in the evolution of intelligence.

Like the higher mammals and the other primates, humans have a relatively massive neocortex.

A schematic representation of this picture of the human brain is shown opposite, and a comparison of the limbic system with the neocortex in three contemporary mammals is shown above.

The concept of the triune brain is in remarkable accord with the conclusions, drawn independently from studies of biain \o body mass ratios in the previous chapter, that the emergence of mammals and of primates (especially humans) was accompanied by major bursts in brain evolution.

Indeed, with rare exceptions (chiefly the social insects), mammals and birds are the only organisms to devote substantial attention to the care of their young-an evolutionary development that, through the long period of plasticity which it permits, takes advantage of the large information-processing capability of the mammalian and primate brains.

But on the whole, mammals show a strikingly greater degree of parental care than do reptiles.