If Homo Erectus Lost His Penis Bone, Does That Mean Men Are Naturally Monogamous?

Some scientists have a bone to pick with the complicated relationship between social behavior and biological change.

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Conventional wisdom has it that men are biologically wired to spread their seed widely, while women put a stress on quality over quantity and therefore developed advanced filtering capabilities. This paradigm has given rise to the theory that man, or unfortunately men, are not biologically “built” for monogamy. In the same vein a theory has developed that women like funny guys because from an evolutionary perspective a sense of humor is a marker for desirable paternal qualities.

Recently there’s been evidence in the opposite direction that focuses on the penis bone (baculum). An article in the Guardian earlier this month described research conducted by scientists at University College London, who traced the development and disappearance of this bone in a variety of mammals. Details of the research are published in Proceedings of the Royal Society.

The penis bone, they said, was important to mammals that need to engage in prolonged, deep penetration aimed an efficiently impregnating the female before another male gets to her. When monogamy emerged as the dominant reproductive strategy among homo erectus nearly two million years ago, the threat posed by other males to a relationship was reduced, and human males lost whatever penis bone they may have had from lack of use. The article ends with the piquant fact that human males penetrate their mates for less than three minutes.

One second, what does this have to do with monogamy? After all, the fact that the male isn’t competing with other males doesn’t mean he’s having a relationship with only one female at a time. A Skype interview with researcher Matilda Brindle supplied the missing link: What they found, she said, was that either monogamy or polygamy explain the reduction and disappearance of the penis bone. She noted that human beings tended to be polygamous or monogamous.

So the first conclusion is that we must ignore the conclusion presented by the article, which points to monogamy as being responsible for the disappearance of the penis bone. But can one make any connection between the elimination of the penis bone and a reproductive method, whether it be monogamy or polygamy?

“I’m skeptical,” said Prof. Yoel Rak, an export on anatomy and human evolution at Tel Aviv University’s Sackler School of Medicine. “This explanation is intellectually interesting but not persuasive. We also lost our tails, and men still have nipples even though they don’t use them. Incidentally, the female chimpanzee also has a bone in the clitoris.

“To connect an anatomical change to behavior is often very problematic, and I say that as a sociobiologist,” he continued. “I recently read a theological essay that said the penis bone disappeared in man because this was the ‘rib’ from which woman was created. I’m not sure that’s a less successful explanation.”

Prof. Hava Yablonka, an evolution researcher at the Cohn Institute for the History and Philosophy of Science, also at Tel Aviv University, notes that higher primates have small penis bones. “Dwarf chimpanzees have a penis bone 6 to 8 millimeters long, and the gorilla’s is 5 millimeters; among chimpanzees everyone mates with everyone while gorillas exhibit classic polygamy. So what does all this mean? That we, too, don’t know how homo erectus reproduced; there’s lots of speculation, but no knowledge. That’s why it’s hard to state that he ‘went over’ to monogamy or any other type of reproduction,” she said.

The question of whether there was or wasn’t a penis bone is perhaps secondary to a broader question: How much can we conclude from an evolutionary study about man’s “natural preferences” for monogamy, or for chocolate or carbohydrates, either?

“Their article deal with mammals; humans aren’t mentioned, and that’s no coincidence,” said Yablonka. “They are evolution researchers who did very nice phylogenetic work, but in media reports they didn’t restrain themselves and slid into unsubstantiated interpretations regarding the animal that most interests the human reader.

“There are two things that cannot be ignored when making extrapolations like this from animals to human beings,” she continued. “One is that man is an animal that fashions his environment both physically and ideologically, and his biological evolution is intertwined with cultural evolution over the past two million years or so. The second is flexibility. There is, for example, a certain species of small bird that under certain food conditions is monogamous, but in others is polygamous or polyandrous [a female mating with several males]. That’s a bird, right? Now imagine what it’s like among people.”

Does all this mean there are no biological or behavioral differences between women and men? No. Does it mean that monogamy is suited to everyone? For sure not. What this does mean is that one must be extremely careful when trying to connect the two using an evolutionary theory. Moreover, even if one finds a difference on average, this doesn’t mean you can make any firm conclusions about a specific man or woman.