There are days when a woman looks in the mirror and the reflection smiles at her, which is not always the case. For no apparent reason, on those days she sees herself more beautiful, happier. She has started getting ready to go out early because she wants to indulge in grooming, choosing the right clothes to wear and trying out different lipsticks. All this while she dances. The sweet life Fedez’s message ringing on your phone. Aware of your good mood, you might wonder: am I ovulating?
If you’re wondering, you don’t know. You could try to remember the last day you had your period and do the math, but even then you wouldn’t be sure, because the cycle has its irregularities. And we live in a time when there is a lot of knowledge about what happens in a woman’s uterus each month. In the 19th century, It was common to think that the most fertile period occurred during menstruation.
If we were chimpanzees or bonobos (genus Bread), our closest relatives, we would have no doubt. With ovulation, the external area of the genitals of these primates fills with water, creating a protuberance so striking that it is impossible not to look at it. Their body announces their peak of fertility in a loud way, both to themselves and to the males.
But we, the females of Homo sapienswe have hidden ovulation. This does not mean that our body is totally indifferent to the hormonal changes of the menstrual cycle. Several studies have shown During ovulation, we have a more attractive body odor, our skin and hair look better, and our movements are more sensual. But these changes are so subtle that they often go unnoticed.
During the second half of the last century, especially in the 1980s and 1990s, the scientific community was speculating about the evolutionary origins of concealed ovulation in humans and its adaptive value. A host of hypotheses were put forward in a heated debate that ultimately led nowhere. Most proposals were based on the idea that chimpanzees were living fossils of our ancestors. That is, we descended from an ape that had genital swelling during ovulation, but that at some point in our evolution, this characteristic ceased to be adaptive and we began to have concealed ovulation.
The American zoologist Richard D. Alexander proposed in 1979 the male investment hypothesis. According to him, females who concealed ovulation were able to get males to protect and watch over them throughout the cycle, not just during ovulation. Males had no choice but to keep an eye on the female all the time if they wanted to ensure paternity. A few well-timed copulations were no longer enough. For other authors, such as the British ethologist Desmond MorrisWe lost the bloat simply when we became a monogamous species and sex began to have the function of strengthening the bonds of a couple. We began to have relations throughout the menstrual cycle and it no longer made sense to announce our peak fertility.
The investment of man
Sarah Hrdy was very critical with these ideas. This American primatologist, tired of the constant portrayal of women as monogamous, passive beings at the service of men, suggested that hidden ovulation benefited females by allowing them to confuse paternity. By mating with different males throughout the cycle, they could not know if they were the fathers of the offspring and the probability of infanticide was reduced.
Nancy Burley was also not convinced by Morris and Alexander’s hypothesis, as they did not give much importance to the fact that ovulation is also hidden from us. Humans are known for having particularly dangerous births. According to BurleyAs soon as we gained intelligence, we began to avoid copulating on fertile days so as not to get pregnant. Females that had more difficulty detecting these days ended up having more children, and over time, the ability to know this was lost.
What if it had nothing to do with sexual behavior? For the Polish biologist Bogusław Pawłowskihidden ovulation in our species was a consequence of bipedalism and the increase in fat in the gluteal area. The erect posture changed the position of the female external genitalia, hiding them between the legs. The swelling became useless and a hindrance to walking.
Finally, there is the possibility that all the apes of our lineage had more or less hidden ovulation. There are several scientists, as anatomy professor Andrew F. Dixonwho have opted for this option, since neither gorillas, nor orangutans nor gibbons present swellings like those of chimpanzees. In this case, we would have to focus on explaining why in the genus Bread This feature has evolved but not in humans.
Female rivalry
Little by little, the debate cooled down without anything clear being reached and this issue has hardly been discussed so far this century. There are some exceptions. In 2021, an article in Nature He proposed the hypothesis of female rivalry. Females of many primates tend to be more aggressive towards those who show signs of ovulation, as this makes them more attractive to males. Therefore, hidden ovulation may have been an advantage because it allowed us to escape these aggressions.
With the new advances in research and technology, the horizons of knowledge have been expanded and it makes sense to revive the debate. We already know that sex outside the fertile period is not exclusive to humans, as was thought, but occurs in more species of primates. In fact, it is documented that chimpanzees copulate even if they do not have genital swelling. Hidden ovulation is not a quality that we can appropriate either. This trait has appeared several times in primates that have very different sexual and social behaviors. For example, it occurs both in marmosets that are monogamous, and in vervet monkeyswho are promiscuous.
As paleoanthropology advances, the idea that we descended from a quadrupedal ape is increasingly questioned. The latest findings indicate that our common ancestor with chimpanzees was a bipedal brachiator like gibbonswho hang from branches when they are in trees, but walk on two legs when they come down to the ground. We probably never walked like chimpanzees and gorillas.
These findings support the view put forward by Dixon, which fits very well with Pawlowsky’s vision. It makes sense that we came from an ape with no genital swelling or only a very small swelling if it moved bipedally. When we look at a chimpanzee, we shudder to feel that we are seeing our past. And when a chimpanzee looks at us, is it seeing its own?
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