Let us begin this hasty preview by focusing our eyes on a distance of say 500,000 years. We might, of course, have taken 1,000,000 or even more years, but I prefer to be modest. On the other hand, some of my readers, no doubt, are slightly myopic and will have little interest in a world as remote as this. They will find it difficult to feel grand-paternal toward their great 16,666 grandchildren. But let them remember that even their own children may resemble themselves as little as their future descendants. And yet who would deny their interest in their offspring. But my real reason for not limiting our vision to 1,000 or 10,000 or even 50,000 years hence is that it would be rather difficult in the hasty glimpse, which are about to take, to find much in the way of interesting differences. For man does not change very rapidly, and we must allow him sufficient time to undergo a few modifications.
As a matter of fact when we look back over man’s dilatory path we are somewhat amazed that although, measured in time, long eras have passed since the upper Paleolithic Age, yet in the way of modern improvements the gain seems negligible indeed. We must perforce delve even deeper into the human past—to the period of Neanderthal Man and even earlier to the days of Pithecanthropus—before sharp differences from Homo sapiens appear to the unprofessional eye.
It is rather difficult to determine whether the rate of man’s evolution has been slower or faster than that of other creatures. Certainly in contrast with some of the lowly molluscs, such as the brachiopods for example, man has been a veritable greyhound, nor has he, compared with the horse, shown any tendency to lag. We must conclude that man’s capabilities for advancement are excellent, but that evolution is a slow process requiring great stretches of time to manifest itself. If, therefore, my picture of the average man of 501,933 A.D. does not conform to your esthetics, you can at least take comfort in the thought that the man of 6933 A.D. will be but little different from what he is today, and for most of us that is far enough ahead to worry about.
The Distinctive Traits of Man The most striking changes which have occurred in the evolution of man from a four-footed (or four-handed, if you prefer) primate to his present proud estate are the marked increase of the brain and the assumption of an upright posture. Upon these developments a numerous series of subsidiary changes are dependent. But these two, upright posture and highly evolved brain, more than anything else distinguish man anatomically from his anthropoid predecessors. And of the two I am inclined, perhaps cynically, to hold that the upright posture is the more distinctive. From that remote day in the past when our ancestral anthropoid stock left off using its forelimbs in locomotion and stood up on its own hind legs the upright posture has remained essentially the same. Although the structure of those enterprising primates had been, to some degree, prepared for such an upward step by a long arboreal tutelage, nevertheless one can readily apprehend the repercussions which that event would have on numerous skeletal traits and internal organs, and one can appreciate the pains of adjustment which would follow. For this new mode of progression made it necessary among other rearrangements, for the foot to develop into a more firmly knit and resistant mechanism, for the pelvis to take on an increased weight-bearing function, for the thorax to become flattened and for the internal organs to be suspended in the longitudinal axis of the body. The point is that although all sorts of accommodations, some of which are still imperfect, were slowly being made in the structure of these early bipeds, the very stimulus to these gradual alterations remained unchanged. In other words, man having achieved this step, did not proceed further along that road for the simple reason that he couldn’t. Once the upright posture is attained one can’t go on becoming more and more upright.
The brain, however, underwent no such circumscribed development. It merely expanded slowly. And while the upright posture has remained fixed, the brain, on the contrary, has continued to increase in size and complexity. For this reason the brain and its enclosing skull are areas where the most significant changes have taken place during the more strictly human history of man.
A Larger Brain I can venture, therefore, with some confidence to predict that man in 500,000 years will continue to be an upright creature, and with some hesitation that his brain will be larger. The reason for my slight hesitancy with regard to the expansion of the brain in the near future (for 500,000 years is but a few days in man’s phylogenetic existence) is that there are some indications that the quality of the brain may improve without a concomitant increase in size. Moreover, Keith has shown that among the Bushmen, for example, the cranial capacity of their ancestors was much greater than is their own. Furthermore, Rhodesian man and some of the Neanderthal burlies of 50,000 years ago had skulls the size of which were equal to if not greater than our own. But in general the tendency from Sinanthropus and Pithecanthropus to modern man has been for the brain to expand. Actually the cranial capacity of Pithecanthropus was about 900 cubic centimeters (roughly 1000 cc. in Sinanthropus), appreciably larger than the average for gorillas, 500 cc., and than that for chimpanzees, 400 cc., but much smaller than we find commonly among Europeans, 1450 cc. If we accept the recent estimates that Pithecanthropus lived at the end of the Pliocene or the beginning of the Pleistocene, a matter of 1,000,000 years ago, we might, by the assumption of a constant rate of increase and with the aid of simple arithmetical processes, arrive at a capacity of 1725 cc. for our future man 500,000 years hence. But this need not call up a picture of a balloon-headed individual. There are men to be met without special comment on the streets today whose skull capacity reaches and even exceeds this figure.
Changes in Skull Shape Professor Arthur Thomson investigated some years ago the effect on the skull of an increased capacity. He found by a simple experiment that if the base of the cranium were kept constant, the cranial vault tended to become rounder as its capacity expanded. The mechanics of this experiment have been amply supported by a number of statistical studies yielding high correlations between head form and cranial capacity. We can, therefore, assume that our hypothetical “homo futurus” will have not only a larger head or brain case but a rounder one as well. The corollary of these investigations is clear. If the capacity remains constant and the skull base decreases in length we have in effect the same result as increasing skull capacity on a fixed skull base. Actually the modern European skull base reveals a marked shortening. In the Neandertaloid skull, known as La Chapelle aux Saints, the skull base is 123.4 mm. long, in the adolescent Le Monstier specimen of the same stock it is 124.0 mm; whereas in the succeeding Upper Paleolithic males it averages 104.8 mm. and in modern Europeans from about 94 to 102 mm. This reduction is convincingly paralleled by a rise in the cranial index. Moreover, there are other signs indicating the way the evolutionary wind is blowing. Recently attention has been focused on the increasing brachycephaly or round-headedness in various parts of Europe. Parsons has noted this phenomenon in modern England where there can be no question of a recent brachycephaly introduced by an invading population. Fischer has similarly reported for southern Germany. We can, therefore, assume that our hypothetical “homo futurus” will have not only a larger head or brain case but a rounder one as well.
Other Changes in the Skull Pari passu with the expansion of the skull, which I anticipate will continue into the future, there has been a refinement of the modeling of the skull. The angular and crude primitive cranium has gradually been converted into a smoother and more gracile one. I shan’t go into all the ways in which this has taken place. That would require a volume. But an important change readily noticeable to the average observer has been the reduction of the prominent bony ridges over the eyes, which in anthropoids and fossil men resemble a heavy bar. At present the female of the human species tends to have a brow that is more or less vertical and smooth above the eyes; whereas in the male there is a moderate swelling above the root of the nose in the region called glabella. To either side of this glabellar area vestigial ridges of bone still persist in the modern male. It is a well marked sex difference and is clearly apparent. With the aid of our evolutionary series we notice that there has been a consistent expansion of the frontal region and a smoothing of the brow as we advance from the primates to modern man. In this respect the female has always been in advance of the male and has pointed the direction in which he has traveled. The ladies may take pleasure in contemplating that it will have taken the males 500,000 years to attain the smoothness of brow which they now possess. As for the females themselves, if a sex difference in the frontal region of the skull is to persist, they will develop infantile brows—slightly bulbous.