Women are known to live 5 to 10 years longer than men. One of the reasons for this asymmetry has been revealed.
How We Get Our DNA
It is fairly common knowledge that we inherit half our DNA paternally and the other half maternally. There is actually a correction to that — we inherit half of what is called nuclear DNA from our fathers and the other half from our mothers.
Mom, Give Me My Mitochondria!
The DNA that encodes for most of the genes in our body exists in a compartment of the cell called the nucleus. Almost all the diverse functions in our body in some way lead from the sequence of this DNA. Almost all, but respiration. Respiratory genes of our body lie in another compartment of the cell called the mitochondria. The mitochondria comes with its own set of DNA, and this set is inherited directly from the mother. This is because of the mechanism of fertilization. It is only the nucleus of the sperm that fuses with the mother’s egg cell to produce the first baby cell (also called a zygote).
How Are We Protected From Mutations?
Moving on to mutations, evolution selects against a mutation in a gene if it is harmful to the organism. A little simplistically, if a mutation in a gene affects the mother or the father, then it will have less chances of being passed on to the next generation. An extreme example of this would be if an individual has a mutation that causes individuals to die young. Since people with these mutations would reproduce less, it would never be allowed to become widespread in the population.
When you bring mitochondrial genes into the mix, you get something interesting. Mutations in the mitochondrial DNA that affect only males have no harmful effects in mothers. Thus, a woman with such mitochondrial mutations would simply pass on such mutations without any “weeding” taking place. Over generations, you could see an accumulations of such mutations which would affect males, but they would have no selection pressure on them because of their transmission through females only.
Fruit Flies Show Anti-Male Mutations in Mitochondria
This is exactly what researchers have found in fruit flies. They compared 13 populations of fruit flies with identical nuclear DNA but different mitochondrial DNA. After growing them in identical conditions, they computed longevity of these populations and found that female flies lived longer (on average, they lived 11 days longer than male flies— a significant difference in the fly life span!). Thus, sex-specific patterns of aging are because the mitochondrial DNA have mutations that affect some component of aging in males, but are either neutral or beneficial in females. Mitochondrial genes are often linked to aging, because respiration leads to the production of toxic substances that can damage our DNA. Respiration is ‘oxidising’, that’s why we hear so much about using anti-oxidants to prevent aging.
This points to a sex-specific sieve that could contribute to differences in life spans between the two sexes. You can read about this research here.