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We're Getting Closer to Solving The Mystery of The Hanging Testicle
The scrotum is a mystery. Why do most male mammals have their reproductive glands so vulnerably located in a sack of skin and muscle outside the body?
According to new research, the answer might be found in those unusual mammals that have testicles located inside the abdomen. These includes elephants, aardvarks and others from a group that originated in Africa, known as the Afrotheria.
Testicles function best when slightly below body temperature. But we can't say for sure this is why mammals evolved descended testicles, not least because males without scrota can still successfully reproduce.
External testes may also be a way of showing off to potential mates, or to protect them from pressure inside the body created by movement.
The new study, published in PLOS Biology, examined 71 placental mammals for two key genes – RXFP2 and INSL3 – that are needed for the development of ligaments involved in testicular descent. They found that in many afrotherian mammals without external testes these genes had mutated to the point where they would no longer function.
This data showed that the common ancestor of all afrotherian mammals, which may have lived 70 million to 90 million years ago, as well as the much older ancestor of all placental mammals, did have descended testicles.
The research also showed this trait was reversed at least four separate times throughout the evolution of certain afrotherian animals. This suggests that studying Afrotheria and their ancestors in more detail might reveal exactly what the evolutionary advantages and disadvantages of having testes outside the body really are.
The scrotum is a mystery. Why do most male mammals have their reproductive glands so vulnerably located in a sack of skin and muscle outside the body?
According to new research, the answer might be found in those unusual mammals that have testicles located inside the abdomen. These includes elephants, aardvarks and others from a group that originated in Africa, known as the Afrotheria.
Testicles function best when slightly below body temperature. But we can't say for sure this is why mammals evolved descended testicles, not least because males without scrota can still successfully reproduce.
External testes may also be a way of showing off to potential mates, or to protect them from pressure inside the body created by movement.
The new study, published in PLOS Biology, examined 71 placental mammals for two key genes – RXFP2 and INSL3 – that are needed for the development of ligaments involved in testicular descent. They found that in many afrotherian mammals without external testes these genes had mutated to the point where they would no longer function.
This data showed that the common ancestor of all afrotherian mammals, which may have lived 70 million to 90 million years ago, as well as the much older ancestor of all placental mammals, did have descended testicles.
The research also showed this trait was reversed at least four separate times throughout the evolution of certain afrotherian animals. This suggests that studying Afrotheria and their ancestors in more detail might reveal exactly what the evolutionary advantages and disadvantages of having testes outside the body really are.
