The incest taboo and the origin of the human species

Anthropologists’ interest in the incest taboo has been described as bordering on obsession. It used to be believed that the incest taboo is a universal taboo. However, some anthropologists have successfully refuted this view, pointing out that what seems universal for human societies is the avoidance of sexual relations between very closely related individuals. It has been shown that in many cultures where the incest taboo is not formally expressed, close relatives still seem to avoid sexual intercourse, especially when such relatives have lived together most of their lives. Anthropologists have also noted that human societies tend to spend more effort spelling out incest taboos with respect to what has been termed “fictitious kinship.”

The Westermack effect refers to the observed tendency of closely related people, especially closely related people who have lived together continuously, to avoid sexual intercourse. The Westermack effect, however, raises some fundamental questions about heterosexual mating patterns in prehistoric human societies.

The total world population of humans is estimated to have been less than 10,000 about 60,000 years ago, having witnessed a significant bottleneck. Prehistoric human societies are also generally thought to be small and scattered with many small societies living, relative to modern standards, in almost complete isolation. Social scientists have pointed out that even in the 19th century, most people lived and died in the societies in which they were born and almost never traveled. Many rural societies today are very small, with populations of a few hundred to a few thousand. It is believed that most prehistoric human societies were even smaller and more isolated. This raises the important question: how did the so-called Westermack effect impact heterosexual human behavior in prehistoric societies? If the size of the prehistoric human population was very small and isolated, how did people avoid incest under the supposed compulsion of the Westermack effect?

It is hard to believe that the Westermack effect could have been so compelling as to prevent a biologically close relative from reproducing by consanguinity in prehistoric times. Even in historical times, we find that populations that are socially isolated, rather than physically, tend to interbreed. Incestuous marriages were common among the upper classes of Ancient Egypt, for example, especially in royal families. These royal families were not physically isolated from the rest of the population, only social class factors isolated them enough to resort to incestuous mating. The same pattern is observed among the royal families of Europe.

Thus, it would appear that isolated human populations unscrupulously resort to what would be termed incest in the culture of larger populations of interbred people. We have good reason to believe that the categories of heterosexual relationships that we would now call incest must have been relatively common in prehistoric societies.

There is evidence to believe that the incestuous mother-child marriage had been part of the magical fertility ritual of prehistoric Palaeolithic man, and that such incest was common enough to significantly impact human evolution, especially with regard to the juvenilization of the human species. Circumstantial evidence for this conclusion is found not only in the widespread myths of the divine incestuous mother-child couple in the early historical Mediterranean world, but also in a detailed examination of the heterosexual dualistic philosophy of fertility cults. It would appear that the intensity of inbreeding associated with incestuous rites of worship had played an important role in stabilizing the human gene pool.