Several mammal species have lost the genes needed for a ligament that controls testes location
Scientists have long wondered what the earliest mammals’ balls were like. After all, a few species today live with theirs swaddled safely up by the kidneys, like elephants do. Most other mammals drop their testes to the lower abdomen to a spot under the skin — like seals — or into an extra-abdominal sack called the scrotum — like humans. What style came first has been a topic of debate.
Now, new research on the genetic underpinnings of testes locations suggests that the male ancestor of placental mammals sported one of the descended modes. “For sure, the [ancestor’s] testes wouldn’t be close to the kidneys,” says Michael Hiller, a computational biologist at the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden, Germany.
The evidence comes from comparing the genetic instruction books, or genomes, of 71 mammalian