In recent decades the pursuit of anthropometry has declined, except for applied anthropology. Instead of measuring the bodies of the last remnants of aboriginal populations, anthro-pometrists measure military personnel and civilians in order to design railroad and airplane seats and space suits. Doctors of Philosophy have become tailors to the new age of science. On the other hand, the pursuit of human genetics has become popular, particularly the study of the frequency in populations of blood-group genes, taste thresholds, mid-digital hair, and hairy ears.
In tracking down the lines of descent of fossil men, none of these characteristics is useful. Thieme and others have shown that it is impossible, using present techniques, to determine the blood type of samples of bone, for they all tend to absorb a group A substance from the ground.2 Dead men cannot taste noxious chemicals, and the hair on their fingers and ears has long since decayed. What could be done, however, is to work out the relationships between fossil specimens and populations in terms of details of tooth structure, for teeth do not change with age except to be worn down. Molar cusp-numbers, the presence or absence of a kind of curvature of the incisors known as shoveling, and many other features that are preserved in the fossil record are just as useful for genetic studies as blood groups are among the living, and paleontologists have long relied on teeth. Although much work has been done on human teeth- no one has yet produced a work of synthesis covering all fossil specimens by means of which they could be compared with living populations.
Limited as the direct application of genetics is in the study of fossil man, the theoretical aspects of that science have helped us greatly. They have taught us that the unit of inheritance is neither the individual nor the arbitrarily chosen type, often identified with an individual, like Nordic, Dinaric, Neanderthal, and Cro-Magnon, but the population, and that each population has its pool
of genes with several possible alternates, known as alleles, from many if not all loci. We also know that because individual mutations recur at characteristic rates, resemblances between populations of the same species do not necessarily imply recent common descent. All curly-haired populations do not have to be descended from a common curly-haired ancestor. Pockets of blondism found among nonwhites need not be explained by Viking invasions, nor all Pygmies be considered as having derived from a single tribe.
An acquaintance with the principles of genetics may also help us solve the central problem of this book—that is, to discover how long ago the ancestors of the human subspecies parted company. We have learned, for example, that evolution proceeds trait by trait, one mutation, recombination, or whatever, at a time. If parallel mutations have been occuring in two populations, we cannot expect a large number of identical changes to have taken place at once in each group. Changes in the skeletons of fossil men from period to period in each major area seem to have involved very few factors, not many of them visible below the neck.
Brains have grown larger and brow ridges smaller. Jaws have sprouted chins and teeth have grown smaller in various degrees. Whole sets of these changes can be linked together as common products of one or more shifts in endocrine balance, shifts advantageous in an increasingly group-oriented society in which self-control comes to be more conducive to survival than a hot temper. Other changes may simply reflect a reduction in chewing, especially after the invention of cooking. If in each of several relateu populations, living in its own territory, changes like these took place not all at once but in sequence, it is possible that each single, parallel mutation prepared the ground for the selective advantage of the one that followed it.
On the other hand, if these sequences of genetic change were initiated in some of the populations by sexual contacts with people from other regions (peripheral gene flow), it would be difficult for us to detect this outside influence from an examination of the skeletons of the resulting mixed population because other genes transferred by the same contact might be disadvantageous in that particular area and would have been eliminated by natural selection. Although we cannot hope to settle the question of parallel evolution versus peripheral gene flow in the evolution of each race bv examining fossil bones and nothing else, such a study may show us how far back in time the various geographical races go. Some of our subspecies are characterized by traits that seem to have had little relation to either climate or culture during the known history of man, and whatever selective advantages or disadvantages they may have must have been acquired long ago. Among these traits are the architecture of the teeth, the shape of the nasal bones, and the degree of flatness of the face. If various combinations of these traits can be seen to have persisted in their special geographical regions despite other changes of a more clearly phyletic evolutionary nature, then the antiquity of individual races may be established. In any case, no form of evidence is unwelcome and only by a close study of detail can we hope to solve this and related problems.