From humans to any other mammal, females tend to outlive males, live longer, are longer lived.
According to a new study , this disparity could be caused by the fact that having two copies of the same sex chromosome is associated with a longer lifespan , suggesting that the second copy offers a protective effect.
Two copies of the chromosome
The idea that a second copy of the same sex chromosome exerts this protective effect is not new, but it has now been shown to be much more widespread than previously believed.
In the study, published in the journal Biology Letters , it is reported that data on sex chromosomes and life expectancy was gathered in 229 animal species , from insects to fish to mammals. Hermaphroditic species and those whose sex is influenced by environmental conditions, such as green turtles, were not included.
The results reveal that people with two same-sex chromosomes live 17.6% longer, on average, than those with two different sex chromosomes or just one sex chromosome.
The team also found that in species where males have two same-sex chromosomes, these males live on average 7.1% longer than females . However, in species where the sex chromosome pattern is reversed, as in humans, females live 20n9% longer on average than males.
The researchers say the extent of the longevity gap may reflect other factors at play, including that men tend to take more risks when it comes to securing a sexual partner .
But there are also other possibilities that can contribute to longevity gaps: estrogen, mainly female-type steroid sex hormones (derived from cholesterol), appears to protect the ends of chromosomes from damage, a process related to aging.