Why some mammal species don’t have descended testicles, but most do | Science News

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Why some mammal species don’t have descended testicles, but most do

Several mammal species have lost the genes needed for a ligament that controls testes location

2:00pm, June 28, 2018
vervet monkey

AIRING OUT  A vervet monkey displays descended blue balls in a thin, unprotected scrotum. The male ancestor of placental mammals also sported descended testicles, rather than undescended ones like a few mammal species, a new study suggests.

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

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