A new survey led by biologists from the University of Bath, do not United Kingdom, points out that Charles Darwin was wrong in his understanding of sexual selection, which are the characteristics that would explain why, for example, male peacocks have such extravagant tails. According to the author of "The Origin of Species", these characteristics are given to increase the chances of an individual find a partner and reproduce.

Darwin believed that these characteristics could be explained by unequal proportions between the sexes. For example, when there are more males than females in a population, they need to work harder to ensure that one of them is their partner and thus ensure sexual relationships and building their offspring.

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However, this new study finds that, surprisingly, sexual selection is more pronounced when sexual partners are plentiful, which means the need to look again at the selection pressures at play in animal populations who have unequal sexual proportions.

Where did Darwin go wrong?

There is no definitive explanation as to why sex ratios are the way they are, but there are some motivational theories for this. Among humans, for example, the fact that women's life expectancy is on average 5% higher than that of men may explain why there are more adult women than adult men. In other mammals, this difference is even greater, with lionesses living up to 50% longer than lions.

Women and lions tend to live longer than men and lions. Credit: Shutterstock

"Despite our growing knowledge of unequal sex ratios, Darwin's insight linking sex ratios to sex selection has received little attention from scientists," the study's lead author, Tamas Szekely, told reporters Science Alert.

“Our study sought to address this, bringing these two strands of the theory of evolution together in order to revisit Darwin's argument,” added Szekely, who is a biochemist and professor at Bath University.

Szekely and his team analyzed 462 different species, including reptiles, mammals and birds, finding a strong association between sexual dimorphism and sex ratios, which would justify Darwin's conjectures.

However, the trend they found was the opposite of that predicted, as the most intense sexual selection, indicated by males much larger than females, occurred in species where there were many more females than males, contrary to what Darwin suggested.

without losing relevance

According to the researchers, this discovery in no way invalidates Darwin's theories about natural and sexual selections. "Our finding simply shows that a different mechanism than Darwin's proposed is driving mating competition for animals that live in sex-distorted populations," explained Szekely.

Larger and heavier males tend to keep all the females in a group. Credit: Wikimedia Commons

More recent theories point out that, in fact, sexual selection is a “winner takes all” system. “This means that when there are many potential mates in the population, an important male, in our study, the largest and heaviest, receives a disproportionately high reward, fertilizing large numbers of females at the expense of smaller males, who may simply not be reproduce”, completes the biochemist.

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