Just three articles this month, all of them related to biology in one way or another. The first one concerns what looks like an evolutionary adaptation in humans to living in the tropics. As this article from BBC News explains, scientists have long known that the birth rates of boys and girls vary across the world and that one of the factors that determine this variance is environmental stress. Biologically, males are considered more fragile than females and since having children is a huge investment, it makes sense that in a harsh environment, women tend to give birth to more girls since they would be likelier to survive.

According to research by Dr. Kristen Navara published in Biology Letters, people who live in the tropics produce more girls than boys compared to more temperate regions, even after adjusting for differences in lifestyle and socio-economic status. As Dr. Navara explains, this could simply be because male sperm works in a different way closer to the equator or that miscarriage rates might be affected somehow, but it could also be interpreted to more generally mean that living in the tropics is itself a form of environmental stress on the human organism.

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