Why do women live longer than men?
In 2011 Census, it was found that men were more than women by 37 million. But, women were more than 1 million as compared to men among those above the age of 60. Various theories have been proposed by scientists as to why women live longer than men. One such theory was that men drink and smoke more. Now, one more hypothesis has been tested that the real reason holds in sex chromosomes.The scientists at the University of South Wales in Sydney published the research in the journal Biology Letters.
In case you have forgotten what a chromosome is, let me brief about it. Our human body is made up of cells. Each cell has a nucleus at its centre. Chromosomes are inside nucleus which holds genes. These genes determine the trait of an individual like eye colour, blood type and sex. It has 23 pairs of chromosomes. Among these, one pair is a sex chromosomes, named X and Y. A female has two X chromosomes(XX) while a male has one X and one Y chromosome(XY).
According to Unguarded X hypothesis, Y chromosome in XY has less capacity to protect an individual from harmful genes present on X chromosome. Since, Y chromosome is small, it is not able to fully cover the harmful mutations present on the X chromosome. This may lead to health threats.
But there is no such problem in XX chromosomes of female. This is because if one of the X chromosomes have withhold harmful mutations, the other X chromosomes, which is healthy, can stand in for the first so that the harmful genes are not expressed. This increases the life span as per this hypothesis.
As per the researchers of UNSW, similarity was found even in amphibians, fish, reptiles where the heterogametic sex does tend to die earlier than the homogametic sex. While the pattern is the same across species, the sexes affected are reverse in case of birds, butterflies and moths. It is the male that has an identical pair of sex chromosomes in them while females didn’t. So female butterflies, birds and moths tend to die earlier than their male counterparts.