More often than not, periods suck. But, as this new Ted Ed video reminds us, they're super helpful and, actually, kind of amazing. You might think that all mammals menstruate, but as the video points out, we're actually among a select few species to partake in this fun little process. It's pretty much just apes, monkeys, bats, and us. Because menstruation is so taxing on our nutritional and physical resources (some of us are pretty much knocked out for a few days every month), it's hard to imagine why we would evolve to rely on it. But it's pretty darn important. In pregnant humans, unlike other mammals, the placenta is directly connected to the mother's circulatory system, which makes a developing fetus potentially very dangerous to the mother's health. So, our bodies have evolved a clever screening system to make sure we only invest our resources in developing the most promising embryos. As part of this system, the endometrial lining is designed to make it as difficult as possible for embryos to attach to the endometrium and develop, ensuring that only the very best survive. But, the video explains, even if it "fails the test," an embryo that makes it to the uterus can still cause infections or send out hormonal signals that mess things up. So, unless a healthy pregnancy develops, the body throws a (totally helpful and necessary) fit: It sheds the entire endometrial lining, cutting out any of those risks and resulting in a period. Dramatic, but worthwhile. Knowing that all this important stuff is happening probably won't make your cramps go away, but maybe it will give you a little extra appreciation for why they're happening. It's just your body taking extra-special care of you!