PROBLEM: Mapping the human genome and advances in human evolution indicate a critical role for genetics in the study of reproduction.
METHOD OF STUDY: Literature in human evolution, genetics and reproduction.
RESULTS: This paper will focus on three points: (1) the course of primate evolution, (2) implications of this course for reproduction in humans, and (3) evolutionary mechanisms. Reproduction is the driving force of evolution, and sex selection is the important factor in determining reproductive activity. The hypothesis will be presented that the reproductive inefficiency of Homo sapiens (one of four pregnancies succeeds) is the consequence of the development of genetic isolation from other species of Homo that was necessary to drive the evolution of Homo sapiens. This hypothesis is based on the evidence that Homo sapiens and Homo neanderthalensis are separate species and that intermating would not yield fertile offspring (Haldane's Rule). This mating barrier involves zoological and linguistic differences and genetic mechanisms preventing fertile interspecies mating (chromosomal incompatibilities, disruption of genomic imprinting and recessive lethal defects).
CONCLUSIONS: The medical and philosophical implications of modern reproductive technologies that may circumvent mating barriers must be addressed prospectively: propagation of genetic defects that would be eliminated by natural selection; the specter of `genetic enhancement'; human cloning; and attempts to control the future direction of the evolution of Homo sapiens.