Reproduction and bonding don’t necessarily go together cites a passage from Jared Diamond’s The Third Chimpanzee (which I’ve been meaning to get, then read) that raises a few eyebrows:
People have many reasons to lie when asked whether they have committed adultery. That’s why it’s notoriously difficult to get accurate scientific information about this important subject. One of the few existing sets of hard facts emerged as a totally unexpected by-product of a medical study, per- formed nearly half a century ago for a different reason. That study’s findings have never been revealed until now.I recently learned these facts from the distinguished medical scientist who ran the study. (Since he does not wish to be identified in this connection, I shall refer to him as Dr. X.) In the 1940s Dr. X. was studying the genetics of human blood groups, which are molecules that we acquire only by inertness. Each of us has dozens of blood-group substances on our red blood cells, and we inherit each substance either from our mother or from our father. The study’s research plan was straightforward: go to the obstetrics ward of a highly respectable U.S. hospital; collect blood samples from one thousand newborn babies and their mothers and fathers; identify the blood groups in all the samples; and then use standard genetic reasoning to deduce the inheritance patterns.
To Dr. X’s shock, the blood groups revealed nearly 10 percent of these babies to be the fruits of adultery! Proof of the babies’ illegitimate origin was that they had one or more blood groups lacking in both alleged parents. There could be no question of mistaken maternity: the blood samples were drawn from an infant and its mother soon after the infant emerged from the mother. A blood group present in a baby but absent in its undoubted mother could only have come from its father. Absence of the blood group from the mother’s husband as well showed conclusively that the baby had been sired by some other man, extramaritally. The true incidence of extramarital sex must have been considerably higher than 10 percent, since many other blood-group substances now being used in paternity tests were not yet known in the 1940s, and since most bouts of intercourse do not result in conception.
At the time that Dr.X made his discovery, research on American sexual habits was virtually taboo. He decided to maintain a prudent silence, never published his findings, and it was only with difficulty that I got his permission to mention his results without betraying his name. However, his results were later confirmed by several similar genetic studies whose results did get published. Those studies variously showed between about 5 and 30 percent of American and British babies to have been adulterously conceived. Again, the proportion of the tested couples of whom at least the wife had practiced adultery must have been higher, for the same two reasons as in Dr. X’s study.