>>11870051It's a genetic defect. There is no purpose. It just hasn't been able to get fully selected out, due to it being situational/random, and due to breeding and raising by humans.
Evolution is efficient but inherently dumb. It's narrowly focused on optimizing certain things, and has no knowledge of the bigger picture. For example, if most animals in a species reproduce by age 3 and then totally stop, but the entire species has a single gene that causes them all to inevitably and immediately die at age 5, that obviously terrible gene could still potentially stick around for millions of years.
