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The evolutionary origin of descending testes



Descending testes were probably present in the earliest mammals, later disappearing into elephants, manatees and their relatives, according to a new study.

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Bull elephant in the Addo Elephant Park in South Africa. They belong to a diverse group called Afrotherian – mammals that live or have originated in Africa – that include manatees and rodent-like insectivores whose testes have been lost over time. Credit Finbarr O & # 39; Reilly for The New York Times

Readers, here's a partial list of things you should not try with elephants: a memory contest, jump rope and castration.

See that elephants, in addition to their eerie memory and their strong relationship to gravity, have their testicles embedded deep in their bodies, right up to their kidneys. This is unusual: in most other mammals, testicles form near the kidneys during embryonic development and then sink to either the lower abdomen or an outer scrotum at the time of birth of a male.

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

A German team that examined the DNA of 71 mammals concluded that the testicular origin is an ancestral form that was later lost in so-called Afrotherians. This group consists of elephants, manatees, and some insectivores that live or originate from Africa

Tinus, a manatee in the Zoological Park in Paris, whose gonads are not descended. Credit Bertrand Rindoff Petroff / Getty Images
A Klippschliefer in Cape Town. Although the Rock Hyrax has no lowered testicles, it has the two inactive genes that are specifically associated with the testes. Joao Silva / The New York Times

Earlier reports on mammalian secrets


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