Women live longer and have a lower mortality rate as compared to men. In the year 2005, the difference in life expectancy between women and men was 5.3 years. If one is to look at centenarians, 80-90% of individuals aged 100 years or older will be female. This is not only true for humans, but is observed for almost all animals on the planet Earth. There are several factors which may contribute to this finding, and they include both societal and environmental factors. Males tend to consume more alcohol, illicit drug, and tobacco when compared to females. This can lead to cancer, lung disease, and cirrhosis of the liver. In addition, male tend to live more violent lives and are prone to die from motor vehicle accidents, suicide, murder, and during combat in war. There is some evidence to suggest that there may also be a biological or genetic basis for the observed difference in life expectancy between females and male. Termed the Mother’s Curse, this theory states that males inherit more lethal mutations in their mitochondrial genes compared to females and thus die earlier.
Researchers, lead by Dr. Damian Dowling from Monash University in Australia, have provide evidence to suggest that there is a genetic basis for the observe difference in life expectancy between females and males. The results of their research were published online ahead of print in the journal Current Biology. The researchers used the fruit fly Drosophila melanogaster to study the inheritance pattern of genes located in mitochondria. They found that males inherit a mutational load in their mitochondria that affects the male aging process but not the female aging process.
The authors wrote, “our results indicate that the mitochondrial mutation loads affecting male aging generally comprise numerous mutations over multiple sites. Our findings thus suggest that males are subject to dramatic consequences that result from the maternal transmission of mitochondrial genomes. They implicate the diminutive mitochondrial genome as a hotspot for mutations that affect sex-specific patterns of aging, thus promoting the idea that a sex-specific selective sieve in mitochondrial genome evolution is a contributing factor to sexual dimorphism in aging, commonly observed across species”.
In order to understand Mother’s Curse and how mitochondrial genes can affect the aging process, we must understand a few things about mitochondria. Mitochondria are the energy powerhouse of cells and supply a large part of metabolic drive for cellular functions. In addition, they have a genome that is separate from the genes located on chromosomes in the nucleus. Mitochondrial genes are passed on from generation to generation only from the female. Males do not pass on their mitochondrial genes. This leaves a selective pressure on mitochondrial genes that is exerted by females, but not by males. In other words, if a mutation in a mitochondrial gene is beneficial for female survival but not for male survival it would still be passed onto the next generation. The authors of the study provide evidence that mitochondrial genes that are harmful to males but not to females have accumulated in the mitochondrial genome and this explains the life expectancy differential between female and males. This finding also gives support to the Mother’s Curse hypothesis.
In the end, it really comes down to one thing:
Females are genetically stronger than males. Period.
M. Florencia Camus et al. “Mitochondria, Maternal Inheritance, and Male Aging” Current Biology published online ahead of print August 2, 2012