Why Women Menstruate ⭕️

1. A handful of species on Earth share a seemingly mysterious trait: a menstrual cycle. We're one of the select few. Monkeys, apes, bats, humans, and possibly elephant shrews are the only mammals on Earth that menstruate. So where's the sense in this uncommon biological process? 2. Pregnancy is always a huge, and sometimes dangerous, investment. So it makes sense that the body should screen embryos carefully to find out which ones are worth the challenge. This is where menstruation fits in. 3. Pregnancy starts with a process called implantation, where the embryo embeds itself in the endometrium that lines the uterus. The endometrium evolved to make implantation difficult so that only the healthy embryos could survive. 4. What happens when an embryo fails the test? As it slowly dies, it could leave its mother vulnerable to infection, and all the time, it may be emitting hormonal signals that disrupt her tissues. The body avoids this problem by simply removing every possible risk. That protective process is known as menstruation. 地球上只有极少数的物种有这种看起来很神秘的特征：月经周期。我们是这少数物种中的一个。猴子、猿、蝙蝠、人类，可能还有象鼩，是地球上仅有的会来月经的哺乳动物。那么，这种罕见的生理过程，究竟意义何在？ 怀孕一直都是一项巨大的，有时甚至危险的投资。因此，身体有理由仔细筛选胚胎，只留下那些值得为之冒险的胚胎。月经则随之产生了。 怀孕始于一个被称作“着床”的过程，在这个过程中，胚胎会嵌入到覆盖子宫内壁的子宫内膜上。子宫内膜不断演化，使着床变得困难，这样只有健康的胚胎能够存活。 当一个胚胎没有通过考验会发生什么？当它慢慢死亡时，可能会使其母体容易受到感染，而且它可能还会一直发出激素信号，扰乱母体的组织。身体为了避免这个问题，就消除掉每一个可能的风险。这一保护过程被称为月经来潮。