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Why Do Humans Go Bald?

When it comes to the evolution of hair loss, a combination of hormones and genetics is to blame.

By Marisa Sloan
Feb 15, 2023 4:00 PMFeb 15, 2023 7:10 PM
Balding head
(Credit: Boreiko/Shutterstock)


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For many of us, hair loss is a fact of life. 

Around 95 percent of the time, hair loss is due to a condition called androgenetic alopecia — also called male or female pattern baldness. And if you’re part of the 80 percent of men or 50 percent of women who experience such hair loss over the course of their lifetimes, chances are you’re not super stoked about it.

The U.S. hair loss treatment industry is booming, after all. Whether you’re talking oils, serums, shampoos or conditioners, according to recent IBISWorld market research, the industry is expected to earn a revenue of $3.9 billion in 2023.

Read More: 20 Things You Didn't Know About... Hair

But if scientists are working overtime to make bald heads a thing of the past, it begs the question: Why did Mother Nature deal us such a bad hand in the first place? Could there be an evolutionary benefit to going bald?

Bald Biology

Let’s start with the basics. Hormones called androgens are primarily to blame for significant hair loss; specifically, an androgen called dihydrotestosterone (DHT), which the body creates from its total supply of testosterone each day.

While DHT is responsible for the growth of hair elsewhere on the body, on the crown of the head it causes hair follicles to shrink — making hair thinner — until the follicle is too small to grow hair at all. This happens more frequently in men simply because they have a greater supply of testosterone, and therefore DHT.

(Younger women naturally make enough estrogen to mask the effects of whatever small amount of DHT is produced. As they get older and produce less estrogen after menopause, however, thinning hair more often makes its unwelcome appearance.)

Of course, we can’t blame everything on hormones. In fact, for more than 80 percent of people who experience hair loss, a father experienced the same. Genetics undoubtedly play a role — though scientists are less sure in what capacity.

Decades of research has pointed to the X chromosome, but there’s more to it than that. A 2017 study of more than 52,000 men from the U.K., published in PLOS Genetics, for example, identified over 250 independent genetic loci associated with male pattern baldness (not all of them on the X chromosome).

And then there are other factors, such as physical and emotional stress or disease. It’s common for those who have just given birth, for example, to experience postpartum hair loss in the months following, according to the Cleveland Clinic

This is likely because hair follicles are cut off from their blood supply and forced into a resting phase prematurely. Similarly, those who are going through certain medical treatments like chemotherapy simply skip over the hair follicles’ growth phase entirely because growing cells are quickly attacked.

Theories of Evolution

Unsurprisingly, the reason that pattern baldness may have evolved in humans in the first place is an even more difficult puzzle to decipher. Typically, traits evolve for one of two reasons: either they help to ensure survival, or they make it easier to find a sexual partner and ultimately create offspring.

Read More: Why Do We Have Fingerprints?

Most scientists agree that there’s little argument to be made for a shiny dome ensuring survival — though opinions on whether it makes a person more attractive have yet to be definitively established.

One 1996 study, published in Ethology and Sociobiology, argued that we inherently associate male pattern baldness with social maturity, a non-threatening form of dominance that has more to do with wisdom and nurturance than aggression. Presumably, this makes men with less hair on their heads more ideal partners.

Meanwhile, the authors of a 2018 study aptly and hilariously titled “Male pattern hair loss: Taking one for the team” assert that male pattern hair loss is an evolutionary nudge directing women to opt for younger partners. 

“Evidence suggests that conceptions by younger fathers are more likely to lead to live births and less likely to result in miscarriage,” they write. “Hence the selection of younger males mediated by the [hair loss] may improve the fitness of the population and of the species at the expense of the individual.”

But rest assured, though science can’t yet answer the question of why humans evolved to go bald, it does offer a solution for those experiencing significant hair loss: Finish what Mother Nature started and shave it all off!

A recent University of Pennsylvania study found that people perceive men with shaved heads as more dominant than those with thinning hair — or even intact, thick hair. So, depending on the look you’re going for, that’s always an option. (Results may vary.)

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