News, Why do men — and other male animals — tend to die younger? It’s all in the Y chromosome

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.

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