Women have an average lifespan that usually exceeds that of men by 5 to 6 years. The ratio of 85 years old women to men is 3:1. This means that for every 3 women aged 85 years, there are 2 corresponding men having the same age. The ratio goes up for centenarians; there are more than 2 women for every one man. There are several theories explaining the difference in longevity across genders. The disposable soma theory, seem to coincide to reality; women seem to be less disposable than men.
The most widely used theory to explain the gender longevity gap is stress. It is believed that men have more stressful working lives in comparison to women. However, if this was to be true, then the gender gap would quickly stabilize as women are increasingly engaging in equally stressful work. Furthermore, women do even have more stress than men nowadays, as they are ‘usually’ more responsible for house work as well. This means women are faced with even more stress than men. The longevity gap should therefore be decreased. Logically, this theory isn’t valid.
The second theory, for women’s higher life expectancy is due to the mode of living. Men do often have unhealthy habits like excess drinking, smoking and unstable diets. However, this is probably not the underlining reason behind the gender longevity gap. For instance, men who are able to live to the same age as older women are usually healthier. Additionally, females of all species do generally enjoy a longer lifespan than males. Lifestyle and diets might thus not be the cause for the disparity in longevity.
Aging as a disease is generally defined as an accumulation of damages to cells, which does in the long run cause cellular damage to our proteins and even DNA. An increasing accumulation of debris leads to damages that are irreparable. Not even the body’s self-repairing mechanism can fix them.
The director of the Institute for Aging and Health at Newcastle in England, Professor Thomas Kirkwood, did in 1977 propose that the body’s repair mechanisms do not work at optimum performance since natural selection supported mostly the reproduction phase of life. According to the natural selection, the essence of life is to pass on genes to future generation as the body itself will only survive for a short period. This was definitely true for the hunter-gathering era, where people were exposed to high risks. Professor Kirkwood named this theory on aging as the disposable soma theory (body is called soma in Greek). In a recent article in the Scientific American, they theory was extended by Kirkwood himself. He explained how the disposable soma theory applies to gender longevity gap.
Studies conducted on long-lived animals at Kirkwood’s laboratory has demonstrated that animals that living longer have a better repair and maintenance system in comparison to those having a shorter lifespan. Furthermore, animals that live longer do also tend to be more intelligent and larger. It is equally common that these mammals have evolved through adaptation. They have developed wings and other mechanisms to circumvent from danger. These long-lived animals are less disposable and seem to have better maintenance abilities. According to Kirkwood, males are genetically more disposable than females (for most species). This is why females live longer than males.
Other laboratory researchers have shown that cells of female rodents tend to have better repair abilities in comparison to males. However, it was found that the longevity benefit of females was cut if the ovaries of the female rodents were surgically removed. Studies have also demonstrated that castrated male animals do usually have a longer lifespan in comparison to animals that haven’t been castrated. Kirkwood, said that information from an institute of mental disturbed people in Kansas claimed that castration of male inmates was very common in the past. These castrated men did on average outlive uncastrated inmates by 14 years.
Scientists in Japan have additional findings supporting Kirkwood’s theory. A super female (mice) was created through the use of genetic materials derived from two females without the presence of any genetic substances coming from males. The super female mice outlived conventional female mice with nearly 30 percent.
Females of different species necessarily need healthy bodies as they have to both bear & nurture future generations. However, the male reproductive role is rather diminutive in comparison so his counterpart (female). Their health is equally short-termed. Professor Kirkwood claims that successful mating as well as rearing of offspring helps to develop a health body which does also increase longevity. The reproductive determinants of men are, on the other hand, less associated to longevity. Additionally, extreme fertility (high level of testosterone) is also linked with shorter lifespan, explaining the higher longevity of castrated men.
According to Professor Kirkwood, the fact that males are more disposable in comparison to female explains the gender difference in longevity.
Source: Physorg
Tue, Nov 23, 2010
Anti Aging Theories