10 Quirks Of Evolution That Are Ruining Your Life

If you've ever wondered why periods are literally bloody hell then you've got evolution to thank for that.

The thing is, most mammals don't get periods, and it actually makes loads of sense. What possible evolutionary advantage could there be to spend a week out of every month in excruciating pain, at the mercy of your hormones and leaving a nice little scent trail for predators whilst you're at it? The answer is pretty complicated but completely fascinating.

Due to the extreme pressures of survival during our evolution, humans are one of the few species with something called a “hemochorial” placenta. Whereas most mammals' placentas have a nice little buffer between them and their developing foetus, the “hemochorial” placenta is a different beast. It literally rips through the blood vessels in the walls of the uterus and wires itself directly into the bloodstream of the mother. This allows the foetus pretty much unlimited access to the resources it needs to fully develop, it can even control her blood sugar.

For this reason, a human pregnancy is an enormous investment from the mother's perspective, it could even kill her. This means that the mother doesn't want to waste her precious time and resources on a weakling foetus, which is where the periods come into it.

We're often taught that the womb lining is there as some kind of cosy welcome mat for the incoming foetus but in reality, far from rolling out the red carpet, the womb lining is actually a brutal testing ground designed to destroy all but the strongest foetuses.

However, if it does succeed in stamping out a sub-par foetus, we're then left with the age old problem of what to do with the body. If it is allowed to sit in the uterus then it could lead to infection, so the best thing to do is haul it all out and start again.

And this, dear friends, is how the woman got her period.