Sep 27, 2026 06:40 PM
https://www.sciencealert.com/mutant-sper...-testicles
INTRO: The competition for dominance starts long before sperm make their last mad dash to reach the egg. Deep inside the testicles, the jostle for genetic survival can start before the sperm themselves are even formed.
Mutations that arise in the stem cells that produce sperm can give those cells an advantage, allowing them to proliferate in a survival-of-the-fittest battle against their unmutated housemates. There's just one problem. What's 'fittest' in the testicles isn't necessarily beneficial to the offspring that those sperm may eventually help create.
A sweeping analysis of mutations in human sperm has revealed that this hidden evolutionary contest is far more extensive than scientists realized. And the consequences could be significant. Many of the mutations identified are associated with developmental disorders – and as men age, these mutations become increasingly common in their sperm, raising the chances of passing them on to their progeny.
The sperm production line never sleeps. Every day, the testes of an adult man can churn out somewhere between 150 and 275 million gametes. Powering that factory are spermatogonial stem cells, which sit along the seminiferous tubules and continually divide, both renewing their own population and producing cells that will go on to develop into sperm.
Every time a cell divides, though, there's a chance that a mutation will arise from slightly janky replication of the DNA. Many of these mutations will be nothingburgers… but every now and then, one pops up that gives the new stem cell some sort of advantage.
That mutant stem-cell lineage can then proliferate at the expense of the surrounding cells, spreading along the tubule and producing more sperm that carry the mutation.
Scientists already knew this could happen. Previous research identified mutations in 13 genes that appear to give sperm-producing stem cells this competitive edge – all of which are associated with severe developmental disorders.
But no one fully understood the extent of the phenomenon – so a team led by computational biologist Matthew Neville of the Wellcome Sanger Institute in the UK embarked on a quest to find out... (MORE - details)
PAPER: https://doi.org/10.1038/s41586-025-09448-3
INTRO: The competition for dominance starts long before sperm make their last mad dash to reach the egg. Deep inside the testicles, the jostle for genetic survival can start before the sperm themselves are even formed.
Mutations that arise in the stem cells that produce sperm can give those cells an advantage, allowing them to proliferate in a survival-of-the-fittest battle against their unmutated housemates. There's just one problem. What's 'fittest' in the testicles isn't necessarily beneficial to the offspring that those sperm may eventually help create.
A sweeping analysis of mutations in human sperm has revealed that this hidden evolutionary contest is far more extensive than scientists realized. And the consequences could be significant. Many of the mutations identified are associated with developmental disorders – and as men age, these mutations become increasingly common in their sperm, raising the chances of passing them on to their progeny.
The sperm production line never sleeps. Every day, the testes of an adult man can churn out somewhere between 150 and 275 million gametes. Powering that factory are spermatogonial stem cells, which sit along the seminiferous tubules and continually divide, both renewing their own population and producing cells that will go on to develop into sperm.
Every time a cell divides, though, there's a chance that a mutation will arise from slightly janky replication of the DNA. Many of these mutations will be nothingburgers… but every now and then, one pops up that gives the new stem cell some sort of advantage.
That mutant stem-cell lineage can then proliferate at the expense of the surrounding cells, spreading along the tubule and producing more sperm that carry the mutation.
Scientists already knew this could happen. Previous research identified mutations in 13 genes that appear to give sperm-producing stem cells this competitive edge – all of which are associated with severe developmental disorders.
But no one fully understood the extent of the phenomenon – so a team led by computational biologist Matthew Neville of the Wellcome Sanger Institute in the UK embarked on a quest to find out... (MORE - details)
PAPER: https://doi.org/10.1038/s41586-025-09448-3