“Stay away from men,” warned Jessie Gallan at the age of 109. According to her, that was the way to live long. And although she might be right, researchers put forward a more plausible explanation in a new study that was published in the journal Biology Letters. They suggest that the sex chromosome type has something to do with the age difference.
The following applies to most animals: animals with two different sex chromosomes – in the case of humans and most mammals that are the Y and X chromosomes – develop as males, the female animals have two identical (X) chromosomes. Those chromosomes are responsible for some physical differences between male and female animals. Besides, they also explain why male animals die faster than their female counterparts. Animals with different sex chromosomes appear to be more sensitive to genetic mutations.
From primates to cockroaches
That is because the same chromosomes can better defend each other so that harmful genes cannot be expressed. To reach that conclusion, scientists at the University of New South Wales in Sydney have scrutinized almost the entire animal kingdom. “We looked at data on the lifespan of primates, mammals, and birds, but also of reptiles, fish, amphibians, arachnids, cockroaches, grasshoppers, beetles, butterflies, and moths,” ecologist and research leader Zoë Xirocostas sums up the list.
What turned out to be? “With a wide range of species, the animal with different chromosomes dies earlier than the animal with the same sex chromosomes,” concludes Xirocostas. However, the mutual differences were substantial. A female cockroach, for example, lives no less than 77 percent longer than its male counterpart. On average, the sex with two identical chromosomes lives 17.6 percent longer.
Nice feather suit and longer life
How do you know for sure that the age difference really has to do with the chromosomes, and not because male animals, for example, live more recklessly? Researchers have checked their position on birds, moths, and butterflies.
After all, the opposite applies here: male birds, for example, have two Z chromosomes, while females have a Z and W chromosome. On the one hand, those chromosomes explain why the male birds have such a beautiful suit, think of a peacock. On the other hand, male birds appear to live 7 percent longer thanks to that pair of identical chromosomes.
So it depends on the chromosomes, the researchers state in their decision. But given that female animal with the same chromosomes live an average of 17.6 percent longer, while that is only 7 percent for male birds, research leader Xirocostas believes that something fundamentally ‘life-shortening’ is still going on in male animals. This hypothesis must be further examined in follow-up studies.