PERSPECTIVES IN BIOLOGY AND MEDICINE Volume III · Number ? · Autumn 1959 THE GUIDANCE OF HUMAN EVOLUTION HERMANNf. MULLER, Ph.D., D.Sc* Even though natural selection has been the great guiding principle that has brought us and all other higher organisms to their present estate, every responsible student ofevolution knows that natural selection is too opportunistic and shortsighted to be trusted to give an advantageous long-term result for any single group oforganisms. Mankind constitutes one ofthose relatively rare, fabulously lucky lines whose ancestors did happen to win out—else we would not be here—while the incalculably vast majority of species sooner or later vanished, without now living descendants. That is, of all the species existing at any one time, only a relatively few ever function as conveyors of germ plasm that is to continue indefinitely, but most ofthese few branch and rebranch to more than compensate for the far greater number that are lost. Do we have reasons for believing that our species belongs in that very limited category that is to continue into the geologically distant future? In examining this question we may first note that man is virtually excluded from ever again splitting into diversified species on this earth, so long as his technological culture remains. For that culture has the effect ofshrinking the earth and removing ever more effectively the barriers to migration and interbreeding. Moreover, besides lacking the multiple chances for success which multiple speciation confers, our single species is undergoing, genetically, something analogous to an increase in entropy * Department of Zoology, Indiana University, Bloomington, Indiana. The author will present this paper at the Darwin Centennial Celebration to be held at the University ofChicago, November 18-24, I059· within itself. For its diverse sublines—hitherto numerous, partly isolated, and to some extent subject to ultimate competition with one another— are increasingly dissipating their separate individualities by merging genetic combinations, so that ever less opportunity is afforded for the intra-species selection among many small groups that has been so potent an evolutionary force. Finally, the rernalning intra-gr'oup selective processes are becoming subject to modification in their direction ofoperation through the influence ofsocial processes which, left to themselves, tend to preserve and in some ways even to aid the multiplication ofcharacteristics that are disserviceable to the welfare ofthe group as a whole—that is, of the species. For all these reasons it seems to follow that the one final remaining line ofman will, ifhe retains or amplifies his technological culture , meet with biological extinction long before the earth grows too hot or too cold to support him. The question arises here, May not this very culture that man has made effect some further alterations in the working ofthe principles ofselection or add features to them that will, after all, permit man's indefinite survival as a civilized being? The answer seems clear. Cultural interference can bring about the survival ofman and his culture only ifit makes consummate use ofman's most distinctive characteristic, his foresight, so as consciously to evade the otherwise inevitable decline. I. Genetic Benefits Resultingfrom Past Cultural Evolution Before discussing what such purposeful action would imply, we may first acknowledge that cultural factors, operating without man's realization of the evolutionary effects they would ultimately produce—that is, without long-range foresight—have in fact exerted major influences on human evolution in the past. And most, although not all, ofthe changes wrought thereby are ofkinds that we would nowadays classify as good. Prime examples are man's facility in using tools, thereby better manipulating the environment, andhis facility in communicating, mainly through speech. Tools and speech themselves are, ofcourse, cultural developments, improved through many generations ofextragenically transmitted experience . The possession ofthese aids to living, even in their more primitive forms, gave increasing scope for the exercise ofthe faculties that produced them and thereby strengthened and sharpened the selection that elaborated further the genetic bases ofthese faculties. Involved here, primarily, were HermannJ. Müller · Human Evolution Perspectives in Biology and Medicine · Autumn 195p mental abilities and proclivities ofdiverse kinds, including the very drives to engage in such activities. For example, the invention of numerical terms and methods ofmeasuring afforded more abundant means...