Why Men (and Other Male Animals) Die Younger: It's All in the Y Chromosome
Arthur T Knackerbracket has found the following story:
According to popular theory, men live shorter lives than women because they take bigger risks, have more dangerous jobs, drink and smoke more, and are poor at seeking advice from doctors.
But research by scientists at UNSW Sydney suggests the real reason may be less related to human behaviour and more to do with the type of sex chromosomes we share with most animal species.
In a study published today in Biology Letters, researchers from UNSW Science's School of Biological, Earth and Environmental Sciences analysed all available academic literature on sex chromosomes and lifespan-and they tried to establish whether there was a pattern of one sex outliving the other that was repeated across the animal kingdom.
Specifically, they wanted to test the 'unguarded X hypothesis' which suggests that the Y chromosome in heterogametic sexes-those with XY (male) sex chromosomes rather than XX (female) sex chromosomes-is less able to protect an individual from harmful genes expressed on the X chromosome. The hypothesis suggests that, as the Y chromosome is smaller than the X chromosome, and in some cases absent, it is unable to 'hide' an X chromosome that carries harmful mutations, which may later expose the individual to health threats.
Conversely, there is no such problem in a pair of homogametic chromosomes (XX), where a healthy X chromosome can stand in for another X that has deleterious genes to ensure those harmful genes aren't expressed, thus maximising the length of life for the organism.
First author on the paper and Ph.D. student Zoe Xirocostas says that after examining the lifespan data available on a wide range of animal species, it appears that the unguarded X hypothesis stacks up. This is the first time that scientists have tested the hypothesis across the board in animal taxonomy; previously it was tested only within a few groups of animals.
Zoe A. Xirocostas et al. The sex with the reduced sex chromosome dies earlier: a comparison across the tree of life, Biology Letters (2020). DOI: 10.1098/rsbl.2019.0867
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