The comparison of the size of the brain in various cases which has just been made is one of absolute size, leaving out of consideration the size and weight of the body and limbs. Putting aside the exceptional pygmy races of man (which there is no reason to regard as primitive), the average adult man is larger and heavier than the chimpanzee, and taller than, though not so powerful as, the orang. The gibbons are quite small--rarely 3 feet in height--but the male gorilla is, when adult, a much heavier animal than man, and often measures 5 feet 8 inches from the heel to the top of the head. Recently even larger specimens have been measured, and 6 feet 6 inches is quoted (probably an over-estimate) as the height attained by some specimens. This fact removes any difficulty about comparing the absolute size of brain in man and these apes. It also renders it unlikely that the primitive ape-men or men-apes were smaller than modern men, whilst the large size and weight of some of the earliest "shaped" flints (of Pliocene age) attributed to primitive man, make it probable that the men who used these flints were larger and more powerful, at any rate in the hands and arms, than modern races of men. Size and strength are, then, not points which offer any difficulty in the passage from ape to man.
What (it may well be asked) is the significance of man's greater brain? What was the advantage to man's ape-like progenitors in an increased volume of brain? It should be noted at once that the pattern of the "convolutions" marked out on the surface of the brain by a great series of winding "ditches" or "furrows" is based on one common plan in the group of monkeys and man--a plan differing from that seen in other groups which have a convoluted brain-surface--for instance from that seen in the carnivora (dogs, bears, and cats) and again from that seen in the ungulates (hoofed mammals). The convolutions of the brain of the higher apes have been minutely compared with those of man's brain. The two sets of convolutions agree very closely, but are less extensive in the apes and certain small tracts of convolutions present in man, are deficient in the apes, especially in the frontal region and at the hinder or occipital region. We know very little of the exact significance of each region of convolution in the brain. The existence of convolutions separated by furrows clearly enough increases the amount of surface of the brain, which consists of a grey substance called "the cortex of the brain," and is known to be a peculiar and specially active material. The mere comparison of the size and height of the frontal region in different animals and in man justifies the conclusion that an increase of this part of the brain is more especially related to increased intelligence. Further, the facts derived from observation of the consequences of disease or of mechanical injury in man have led to the conclusion that the "faculty of language" (the significant use of words, not the mere production of them as sounds) is especially connected with one of the frontal convolutions, which is feebly represented in the apes. The convolutions of the brain of lower races of men have not been very fully studied, but the brain of a Hottentot woman was long ago carefully described and illustrated, showing less complexity of the convolutions than is usual in European man, and making a distinct approach in this respect to the apes; but still possessing in fair proportion the convolutions characteristic of the human brain.