Reader, here’s an incomplete list of things you shouldn’t try with elephants: a memory contest, jump rope and castration.

See, in addition to having uncanny recall and a firm relationship with gravity, elephants have their testicles nestled deep within their bodies, all the way up near their kidneys. That’s unusual: In most other mammals, testicles form during embryonic development near the kidneys and then descend, either to the lower abdomen or an external scrotum, by the time of a male’s birth.

Biologists have wondered about this discrepancy for decades. Did the earliest mammals retain their testicles, like elephants, or did they let their family jewels drop? A new study, published Thursday in PLOS Biology, says it was the latter.

Studying the DNA of 71 mammals, a German team concluded that testicular descent is an ancestral trait that was later lost in so-called afrotherians, a ragtag group that includes elephants, manatees and several insect-eaters that live in or originated from Africa.