Why do women live longer than men? There are many reasons, but having two copies of the same sex chromosome and testosterone might be the most significant.
Obviously, both men and women age. Their bodies undergo similar changes that ultimately result in death. However, across the world, women tend to live on average 8% longer than men. This doesn’t just apply to humans but almost all lifeforms that have male and female forms. Scientists looked at 229 different species of mammal, insects, fish, and birds. They found that, on average, the females lived 17.6% longer. This varies from species to species. In the wild, female lions live for 50% longer than male lions.
So, why do women live longer than men? There appear to be five main reasons.
One reason often given is that men work their bodies harder than women, but this is provably not true. If that were true, the difference in life expectancy would narrow as more women do jobs that men have traditionally done. That is not happening. It would also stand to reason that the difference would not extend through the animal kingdom.
The first reason is that men are larger than women. A larger body means more cells, which gives a greater chance of mutations and cell damage. A larger body also needs more energy and metabolizing food for energy can damage and wear the cells as well. This is not so far fetched because a study that looked at millions of deaths showed that shorter people tend to live longer than taller people. Men are about 8% taller than women on average and women tend to live about 8% longer. This is definitely a reason, but it is not the only reason.
The second reason could be connected to the previous one, but it does not necessarily apply to humans. Males of a species use a lot of energy resources towards sexual competition. In the animal kingdom, a primary goal is to reproduce. The females usually go for the strongest, fittest male, and the males use a lot of energy to be that male. Fighting or having extremely large horns in order to fight are common and can also shorten life expectancy. The males are also more likely to take risks.
A third reason is that estrogen brings a host of benefits. Estrogen protects the heart and other tissue throughout the body by keeping it supple and flexible. Women have less heart disease than men. It keeps blood pressure and LDL cholesterol down. It promotes blood clotting and is an antioxidant. This is one reason why women are more likely to have a heart attack and illnesses after the menopause than they are before it.
A fourth reason is testosterone. Testosterone seems to be a large reason why women live longer than men. A Korean scientist studied 81 eunuchs from the 19th century. He discovered that they lived for 70 years at a time when the average male died at 50. They were 130 times more likely to reach the age of 100 than regular people. The difference in life expectancy between eunuchs was due to the age at which they were castrated. If they were castrated before 15, they tended to live much longer, leading to the idea that testosterone has a big part to play in life expectancy.
So, what does testosterone do? It increases levels of LDP cholesterol, which is the dangerous cholesterol. It increases the power of the immune system and heart in early life in order to facilitate sexual competition, but this comes with a huge drop in both after middle age, increasing the risk of heart disease as men age. It also seems to increase the risk of cancer in later life, especially prostate cancer.
However, the most significant reason for the difference in life expectancy appears to be the presence of two sex chromosomes in women. One cause of aging and death is mutation in the cells. Every time a cell divides, it copies everything within it. A mutation can happen when there is an error in the cell division. Part of the chromosome can break off, be removed, be inverted, or be duplicated or moved onto another chromosome. This changes the structure of the chromosome and can cause genetic disorders or cancers. Women have two X chromosomes while men have one X and a Y. Having two copies of the same chromosome seems to reduce the likelihood of mutations. This is proven by looking at animals. My original question was why do women live longer than men, but it looks like animals with two of the same chromosome live longer than animals with only one chromosome, irrespective of gender. In birds, the male has two Z chromosomes and the females have one Z and one W. Male birds outlive female birds.
So, why do women live longer than men? There are many reasons but the presence of testosterone in men and women having two of the same chromosomes seem to be the greatest reasons. Not something I can do much about. And this is what I learned today.
Sources:
https://pubmed.ncbi.nlm.nih.gov/12586217/
https://www.endocrineweb.com/conditions/heart-disease/heart-hormones
https://ourworldindata.org/why-do-women-live-longer-than-men
https://www.bbc.com/future/article/20151001-why-women-live-longer-than-men
https://www.voanews.com/a/science-health_new-study-looks-why-females-live-longer-males/6186357.html
https://www.bbc.co.uk/bitesize/guides/zc499j6/revision/4
https://www.bbc.com/news/science-environment-52007780
https://www.dw.com/en/evolution-why-females-live-longer/a-52940412