map testosterone

Since the beginning of humanity, there’s been testosterone, one of our most famous hormones. But this year, we learned a lot about T: how it affects what kind of products we buy and how it’s decreasing in young men. Back in June, the authors of a paper in Nature Ecology and Evolution handed down a sobering revelation about testosterone: Where a guy grows up can impact how much his body produces for the rest of his life.

Kesson Magid, Ph.D., a biological anthropology professor at Durham University in the UK, focused his study around testosterone levels from four different groups of men from Bangladesh and the UK: Men who were born and raised in Bangladesh, men who were born in Bangladesh but moved to the UK as children, and second-generation Bangladeshi men raised in the UK. He also compared testosterone levels in these three groups to a control group of ethnic Europeans.

The men who were born in the UK had higher testosterone levels regardless of ethnicity, but those who left Bangladesh after the age of 8 tended still had lower testosterone levels than those who immigrated to the UK earlier in life — despite the fact that they had spent years of their adult lives in Europe.

Bangladesh

In June, Magid told Inverse that he believes this comes down to a “choice” that every man’s body makes around the age of 8, which he describes using the model of Life History Theory. At an early age, the body makes crucial decisions about how to allocate energy — and if the body is concerned with say, fighting off disease, then testosterone production seems to take a back seat. Once the body makes that choice, Magid adds, it seems to stick with it.

“Once a male ‘commits’ a proportion of his investment to reproduction it determines his regular levels of testosterone for the rest of his adult life,” Magid said.

That irreversible decision is one reason that this story ranks 25th in our countdown of surprising things we learned about human this year.

As 2018 winds down, Inverse is highlighting 25 surprising things we learned about humans this year. These stories told us weird stuff about our bodies and brains, uncovered insights into our social lives, and generally illuminated why we’re such complicated, wonderful, and weird animals. This story was #25. Read the original story here.