After age 100, women outnumber men by more than two to one in the U.K. says BBC News. Dudes, what gives?
You could blame healthcare neglect, heavy labor, or hormonal differences, but today in the journal Current Biology a set of researchers suggest male mortality has something to do mutations in mitochondrial DNA.
Mitochondria are our cells’ powerhouses. They turn the food we eat into energy. We inherit all of the DNA for our mitochondria from our mothers.
The British and Australian researchers found a number of mutations in fruit fly mitochondrial DNA that affect how long males live and how quickly they age. These same mutations don’t seem to affect female flies.
Mitochondrial DNA mutations that only harm males fit in a sneaky loophole of natural selection. Typically, natural selection weeds out harmful mutations in DNA.
To give an oversimplified example, imagine a woman born with a mitochondrial DNA mutation that gives her three arms (no, not possible). She happens to find an open-minded man who’s into that, and they have children. Her third arm is passed on to those children, but the chances of them procreating and passing on that mutation are fairly slim. That third arm mutation won’t last more than a couple of generations.
But imagine that the same third arm mutation remains unexpressed in women. The original woman born with the mutation looks normal, meets a mate, and they have children. Her sons are all born with three arms, but her daughters only have two. Her sons may strike out in the dating pool, but her daughters don’t, and they keep passing on the mutation. More and more unlucky men continue to be born with three arms, while women continue to pass on their genes oblivious to the mutation they’re carrying.
In a similar way, mitochrondrial DNA mutations that affect male fly lifespan can continue to amass in the population without harming the females who pass them along.
The researchers suggest the same thing could be happening in other species including humans, propagating a die-early mutation expressed only in males. As the mutations are passed on through thousands of generations, they could eventually affect nearly the entire population of males.
The BBC News points out that there’s at least one skeptic of this theory:
Tom Kirkwood, professor of ageing at Newcastle University said the paper was “intriguing”.
He said: “It may be it does tell us something rather important about mitochondria and the difference between male and female fruit flies. And we know that mitochondria are important for ageing in a number of species. But I certainly don’t think this is a discovery that explains why women live five-to-six years longer than men. There are other things we know also count - lifestyle, social and behavioural factors. But the biggest difference in biology is that we have different hormones.”
[via BBC News]
Photo: Moyer Photos/Flickr