Researchers have found out why women on average live longer than men. According to them, the duplicate X chromosome which is the sex chromosome could be responsible for this. It has been found that with over 200 animal species there is a connection between this genetic trait and life expectancy. The so-called homogametic gender is responsible for getting older which confirms a hypothesis that has been discussed for some time.
Life expectancy also depends on gender. Not only in humans but also in some other mammals, females have an advantage in this context. They usually grow older than their male counterparts. On the other hand, the opposite is true with birds. With them, the males are more durable and long-living. What is the reason behind it? Let’s find out
Two is Better
According to a common hypothesis, the differences in sex chromosomes could be responsible for this strange phenomenon. While male individuals have one X and one stunted Y chromosome in mammals, the female sex has two X chromosomes. In birds, the males are homogametic which means they have two Z chromosomes.
This double presence of the strong chromosome could be the decisive advantage. This means that important genetic factors are available in duplicate. If there are mutations that cause illness on a chromosome, in many cases this can be compensated for by the healthy second variant. With only one X or Z chromosome, this possibility does not exist. This is believed to result in reduced life expectancy for heterogametic sex.
Higher life expectancy
The life expectancy of a total of 229 species from 99 families, 38 orders, and eight classes have now been examined. To do this, the data from scientific articles, books, and databases were collected. If the assumption is correct, the connection between gender and life expectancy should not only be evident in some mammals and birds instead, it should be observed in all living beings with different sexes.
In fact, the evaluations revealed that the homogametic sex with two identical chromosomes lives 17.6 percent longer on average. The heterogametic gender across the animal kingdom has a significantly shorter life expectancy. Chromosome morphology seems to play an important role in this key feature.
Females are lucky
The advantage of sex with a double chromosome is not always the same size but also depends on gender. If males are heterogametic(Humans), they have a life expectancy of around 20.9 percent lower than their female counterparts. If, on the other hand, the females have two different chromosomes(butterflies and moths), they die only 7.1 percent earlier which means that the genetic disadvantage obviously does them less harm.
According to the researchers, there are three possible explanations for this. First, it could be that the Y chromosome is more stunted in animal species with male heterogamy. It means that it has been prevented from developing properly. On the other hand, the female sex hormone estrogen may have a positive effect. It is known that estrogen stimulates the telomerase enzyme which forms the chromosome caps that shield the underlying genetic material from harmful influences.
Sexual competition as a disadvantage?
The third explanation for the disadvantage of men is related to sexual competition. Males take more risks than females in order to take advantage of a reproductive opportunity. For example, many species have fights between competing males.
Higher mortality due to side effects of sexual selection in combination with the influence of chromosomes could explain why the lifespan of males and females of various species are different.
All in all, the results reveal an exciting factor influencing life expectancy and thus provide valuable knowledge. There is a multi-billion dollar industry that wants to extend the human lifespan. But there are still significant gaps in knowledge.
Which biological processes determine life expectancy and what factors contribute to a long life for different genders and species? These findings represent an important step on the way to deciphering the mechanisms that affect longevity. In the long run, this could open up opportunities to extend life. Let’s hope that more answers will be found in our lifetime.