Men lost their spines.

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.


  1. says

    Chimps engage in sexual activity for an average of 8.2 seconds while the average for humans is around 120 seconds.

    Looks like chimps are the champs and humans are the chumps of the quickie.

  2. Stevarious, Public Health Problem says

    while the average for humans is around 120 seconds

    That’s the AVERAGE??

    Dayum. There’s my ‘feel good about myself’ thought of the day.

    But yeah, I would agree that our monogamous/polygamous tendencies are far more influenced by social concerns than biology. Plenty of people would like to be polygamous but choose or are pressured not to be. Plenty of people would like to be monogamous but choose or are pressured not to be.

    Human sexuality seems to me to be far to varied to be described by any single words except ‘complicated’, and it’s hard to think that any of us (being humans an all) are objective enough to really come to any certain conclusions.

    • Nathanael says

      Indeed. Variety. Most people seem to want to believe that “humans are all like _____”. (Variant: “women are all like ____, men are all like ____, people from country X are all like ___”.) In reality, there is enormous variation among individual humans.

      Our desire to generalize appears to be a result of the way our brains work: most (probably not all!) humans have overdeveloped pattern-matching circuits which kick in at the slightest provocation, finding patterns where there are none and converting slim correlations into “rules”. (There is a huge amount of psychology research backing this.)

      I suspect this is the cause of a huge amount of pain and suffering in the world: people who are unaware of these cognitive biases are led by their pattern-finding brains to make huge, untrue generalizations about entire groups.

  3. says

    If you’re talking about multiple partners for women, “polygamous” is incorrect, as that specifically means “multiple women.” You are thinking more of polyandrous, meaning “multiple men.” Or the pop culture term “polyamorous,” meaning (through a bad blending of Greek and Latin root words) “multiple lovers.”

    Also I think statistically in the Western world, 55% of men cheat on a partner at some point in their lives, while 45% of women cheat. Which shows not that women are more monogamous than men, but that we are statistically much closer to each other in multi-partner sexual appetites than we are told. So yes, I think we homo sapiens are not monogamous creatures, although cultural memes seem to have an impressive ability to control our behaviors. I’m not arguing whether this is good or bad, just pointing out the intriguing conflict between various things we have evolved over the millennia.

  4. Debal says

    The Scriptures and Lawbooks tell us:
    “Higamus hogamus
    Men are polygamous.

    Hogamus higamus
    Women are monogamous.”

    The Book of (Human) Nature says different things, and pleads us to enjoy life ….

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