Humans lost their penile spines during millions of years of evolution.
People believed ‘humans evolved smooth penises as a result of adopting a more monogamous reproductive strategy than their early human ancestors. Those ancestors may have used penile spines to remove the sperm of competitors when they mated with females.’ But it is not the reason for losing penile spines. Researchers recently found that the chunks of DNA that had been lost from the human genome but not the chimp genome, was the reason.
They first systematically identified 510 DNA sequences missing in humans and present in chimps, finding that those sequences were almost exclusively from the non-coding regions of the genome, between genes. They then homed in on two sequences whose absence in humans they thought might be interesting — one from near the androgen receptor (AR) gene and one from near a gene involved in tumour suppression (GADD45G).
Inserting the chimpanzee sequences into mouse embryos revealed that the former sequence produced both the hard penile spines and sensory whiskers present in some animals. The latter sequence acted as a kind of brake on the growth of specific brain regions — with the removal of its function appearing to have paved the way for the evolution of the larger human brain.
We got bigger brains so we lost penile spines.
Some scientists say ‘loss of penis spines would result in reduced sensitivity and longer lasting sexual activity.’ But not all penis spines serve quick sex. Orangutans have more penis spines than chimpanzees and yet their average duration of sexual activity is longer than chimpanzees and humans. Chimps engage in sexual activity for an average of 8.2 seconds while the average for humans is around 120 seconds. In contrast, orangutans range between 840 seconds and 2,760 seconds. Humans rank 14th in the duration of sexual activity.
We know now that humans evolved spineless penises not because of adopting a more monogamous reproductive strategy. Humans are not necessarily monogamous. But the debate is still going on. Some say, humans are monogamous. Some say, we are polygamous.
I think humans are polygamous like other apes. But in most human societies many rules have been created to force humans to be monogamous. Some are happy to be monogamous probably because they are indoctrinated to be monogamous. Others are desperate to be polygamous. We often go against nature to create laws. We must not think that something is good or right because it is natural, or that something is bad or wrong because it is unnatural or artificial. In human societies, compare to men, women are more monogamous. I do not think there is any reason to believe that women are naturally monogamous. Vulnerable and dependent women are more monogamous than independent and free women. Not a natural issue, it is a societal issue.