What explains the fact that people are divided only into two sexes?
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Answer 1
January, 2021I do not agree, asexual or bisexual individuals may have the same chances of survival, or even higher - and this is what evolution is tied to. Development is not evolution. In addition, there are organisms with more than 2 sexes - ciliates of shoes have more than 20 sexes. At the same time, individuals participate in their "reproduction" in pairs. For evolution, gene exchange at the population level is important, not the number of sexes.
Sexual reproduction primarily provides an advantage in immunity, allowing individuals resistant to any pathogens to appear in the population. This is the most convenient and simplest and fastest way to protect the population from extinction, since pathogens adapt to the immune system and bypass it very quickly.
Two sexes, most likely because it requires minimal gene input. And of course, evolution is also making its contribution here - some species have lost their bisexuality for the second time - bdelloid rotifers - live and thrive with the same sex, but exchanging genes.
Answer 2
January, 2021One sex does not provide an opportunity for development, since there is no mixing of the gene pool during reproduction, three sexes would create a greater risk for reproduction itself, dramatically increasing the number of factors that should have coincided. Two genders are perfect.