Okay, good to know. But - what purpose do they serve?

Like, humans are born with an appendix, but really we don't exactly have a use for them. They're just a defunct organ that may kill you on occasion if it bursts. So we have them, but no one knows why anymore.

_{[ Perfect example, see? You can't just say "we have tails" and not go into detail. It might be important! ]}