Early Medical Theories
In ancient medicine there was a dispute between the one-seed theory, expounded by Aristotle, and the two-seed theory of the 2nd century A.D. Roman physician Galen. By the one-seed theory, the germ of every embryo is contained entirely in the male seed, and the role of the mother is simply as an incubator and provider of food: on this view only a patrilineal relative is genetically related. By the two-seed theory, the embryo is not conceived unless the male and female seed meet: this implies a bilineal, or cognatic, theory of relationship. It may be significant that Galen lived at about the same time (129 – 199/217 AD) that Roman law changed from the agnate to the cognate system of relationships.
Common to both theories was the mistaken belief that the female emits seed, and not an egg. Additionally that a seed is only produced when she comes to orgasm. Given that assumption, the evidence for the one-seed theory is the fact that a woman can conceive without coming to orgasm (though this was still a matter of dispute in the ancient world and the Middle Ages). The evidence for the two-seed theory is the fact that a person can look like his or her maternal relatives. These two pieces of evidence could not be reconciled until the discovery of ovulation in the early 19th century, confirming the two-seed theory as biological and dissociating the production of female seed from the occurrence of the orgasm.
In early Greek and Roman history, a few philosophers claimed that although every child has one absolute mother, it did not follow that every child had one absolute father ("mater semper certa est"). They suggested that a child's genetic character could be influenced by the seed of two or more men if they had inseminated the same mother. This was considered a fringe theory even in its time, however, and was never widely accepted. Traces of such a theory appear to underline various myths of a hero (such as Heracles) with both a human and a divine father.
Read more about this topic: Patrilineality
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