Genetic differences in humans, like those between individualsof any animal or plant species and those betweenspecies, are all products of the evolutionary developmentof the living world. Th ese diff erences, with their behavioralconsequences, can only be understood in the light of evolution.Our understanding of evolution, however, has itselfevolved. Th e Darwin-Wallace theory of evolution appearedin the nineteenth century. Since then, development ofevolutionary thought has gone through several stages. Th econtributions in this volume describe those stages.

The first four decades after Darwin were dominatedby studies in comparative anatomy, embryology, systematics,zoogeography, phytogeography, and paleontology,all intended to discover and examine the evidences ofevolution. But the phylogenies of the animal and plantkingdoms, that is, the history of the linkages of animal andplant organisms as they change through time, were lesswell documented. In particular, the phylogeny of humansis still not completely known.

The period following World War Two saw accelerationof activity in fi elds in and bordering on behavioral genetics.Research in neuroendocrinology showed that highercortical centers could infl uence and be infl uenced by thehypothalamus, pituitary, thyroid, adrenals, and gonads.Genetic diversity in the function of these organs hadobvious consequences for social and cultural behavior.Th e failure of some early and long-reinforced attempts atconditioning by students of comparative animal behaviorshowed species-specifi c innate behavior could not beignored in any theory that attempts to combine psychologyand anthropology. Th is classic volume summarizesthe development of evolutionary thinking, and describeshow what we know about genetic diversity links up withresearch on human behavior.

J. N. Spuhler was known for his pioneering work in the departmentof anthropological genetics. He taught in many universitiesincluding Ohio State University, the University of Michigan, andthe University of Mexico. He received the National Academy ofScience award for scientific reviewing and his work has appearedin scholarly journals including: Journal of Anthropological Research,Annual Review of Anthropology, and American Journal of PhysicalAnthropology.