As breasts are designed to feed babies, why do women have two instead of just one?
In: Biology
We don’t really know since evolution isn’t a sentient entity that we can ask questions of. We can’t even run double blind trials. In most cases we can’t conduct experiments at all, both because of ethics and the timescales involved.
That said there are a few hypotheses.
The human body develops mostly in a mirror image. Soon after conception the embryo folds in half. The line down the middle becomes our digestive tract and the remains of the seam are visible all along the front from the attachment at the bottom of the tongue down to your taint. After that most things just develop the same way on both sides.
Some mammals have more than 1 pair of mammaries but they tend to have more offspring at a time.
2 breasts provide some redundancy. If an injury keeps you from having offspring that can grow up to reproduce you’ll quickly lose out to gene lines that aren’t as vulnerable to injury.
Twins need two breasts. This one is less likely since, on humans, it’s not really practical for two kids to nurse simultaneously.
Evolutionary psychology has a theory that when humans shifted from primarily rear mounting mating to primarily face-to-face males were still evolved to enjoy the sight of two globes of butt. So human females evolved to have permanently enlarged mammaries (almost unheard of among other mammals) to mimic the butt. This is a kind of silly hypothesis and I haven’t seen any independant support for it but I like it because it lets me talk about boobs and butts at the same time while still sounding somewhat serious.
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