If male pattern baldness is caused by testosterone, why are hairs on top of the head more affected by it and hairs like eyebrows, beard, inside ears etc, are affected less?

Question

If male pattern baldness is caused by testosterone, why are hairs on top of the head more affected by it and hairs like eyebrows, beard, inside ears etc, are affected less?

In: Biology

Answer 1

The general mistake here is to believe that every genetic trait is somehow designed to converge on perfection.

Frequently a trait – such as male pattern baldness – is a trade-off against another more important trait.

So, for instance, a genetic makeup that confers huge strength may also confer male pattern baldness. But the baldness is vastly outweighed by the advantages that huge strength carries.

Now factor in that the increase in lifespan has happened with disproportionate speed (because of technology). If you go bald at 40 but your aren’t expected to hit 30 because of the harshness of the environment, male pattern baldness – or any apparent disadvantage that manifests after the age of 30 – is irrelevant when it comes to giving you a reproductive advantage.

The relative speeds of evolutionary pressure isn’t enough to catch up with technological progress.

So here we are.