It is well known that women live longer than men. I had not been aware that this was not true for all species and that when comes to birds, the opposite is true. Now some researchers are finding new evidence to support an idea that what causes the difference is whether one has an unpaired sex chromosome or not.
From humans to black-tailed prairie dogs, female mammals often outlive males – but for birds, the reverse is true.
Now researchers say they have cracked the mystery, revealing that having two copies of the same sex chromosome is associated with having a longer lifespan, suggesting the second copy offers a protective effect.
…The idea that a second copy of the same sex chromosome is protective has been around for a while, supported by the observation that in mammals – where females have two of the same sex chromosomes – males tend to have shorter lifespans. In birds, males live longer on average and have two Z chromosomes, while females have one Z and one W chromosome.
Scientists say they have found the trend is widespread. Writing in the journal Biology Letters, the team report that they gathered data on sex chromosomes and lifespan across 229 animal species, from insects to fish and mammals. Hermaphroditic species and those whose sex is influenced by environmental conditions – such as green turtles – were not included.
The results reveal that individuals with two of the same sex chromosomes live 17.6% longer, on average, than those with either two different sex chromosomes or just one sex chromosome.
The team say the findings back a theory known as the “unguarded X hypothesis”. In human cells, sex chromosome combinations are generally either XY (male) or XX (female). In females only one X chromosome is activated at random in each cell.
As a result, a harmful mutation in one of the female’s X chromosomes will not affect all cells, and hence its impact can be masked. By contrast, as males only have one X chromosome, any harmful mutations it contains are far more likely to be exposed.
I had also not known that bird chromosomes are identified by different letters than those used for human chromosomes.
You can read the paper here.
It’s not the only place unmatched chromosomes make a difference. Colour Vision Deficiency (colour blindness) is common among XY people (1 in 12) but rare in XX (1 in 200). The recessive trait rarely comes twice.
I thought that a huge part is due to men dying young doing stupid things (like the majority of people getting into serious accidents are men) and also taking less care of their health by drinking, smoking and believing that veggies are going to make them grow tits.
In humans at least, a large component of the difference in life spans is cultura rather than biological. Men are raised to be stoic and brave, and both of these lead to reduced health as a trend. The first makes men generally more reluctant to talk over issues, both psychological and physiological, leading to increased suicide rates and health issues going undiscovered for longer; the second leads to increased risk taking and so to increased early deaths due to accident.
I wonder sometimes what the trend would be without them, but alas that can only really be ascertained in some hypothetical future where such expectations are not foisted on the sexes.
#1
All sorts of genetic conditions are increased in men due to that heterogeneity.
The importance of this research is that it covered a lot of different species, 229 including insects, fish, birds and mammals, and the difference was found in all of the species, so while all of the reasons that have been proposed for why human males live shorter lives than human females may have some validity if we eliminated all of those reasons there would still be a difference.
I’d imagine a fair amount of the difference also comes from some of the health risks that go along with higher testosterone partners. One of the first things they made clear to my partner before his transition was that taking testosterone would put him at significant risk of various illnesses and conditions.
Giliell @2
Same, and experience tends to support this theory.
Another chromosome story just came up, about komodo dragons (WZ and ZZ). At a zoo, a mom gave birth parthenogenically.