![marlene zuk animal models and gender marlene zuk animal models and gender](https://d3i71xaburhd42.cloudfront.net/2b29e79aefffcf4a09c1b1bcafc65db2433f67c3/9-Table1-1.png)
Variance in male reproductive success is thus expected to be higher, on average, than variance in female reproductive success, which in turn selects for what might be termed a “live hard, die young” overall strategy for males, at least with respect to mating behavior. Because each mating requires relatively little investment from him, a male who mates with many females sires many more young than a male mating with only one female. Males, on the other hand, can leave the most genes in the next generation by fertilizing as many females as possible. Which male they mate with could be very important, because a mistake in the form of poor genes or no help with the young could mean that they have lost their whole breeding effort for an entire year.
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Because they are the sex that supplies the nutrient-rich egg, and often the sex that cares for the young, females will usually leave the most genes in the next generation by having the highest quality young they can the upper limit to the quantity is usually rather low. Female reproductive success is limited by the number of offspring a female can produce and rear. Some researchers are hopeful that the gap between men's and women's lifespans will close as we develop better medical care and education about health risks, but I will argue instead that the disparity is not going away any time soon.Ī subset of evolutionary theory called sexual selection holds that females and males usually inherently differ because of how they put resources and effort into the next generation, which is termed parental investment. Below I discuss an evolutionary approach to the question of why males so often die sooner and develop more diseases than females. Sex differences in infection rates or mortality may come about for the same reasons as other differences between males and females, such as morphology: selection acts differently on the sexes because they maximize their fitness in different ways. What causes this disparity between the sexes in longevity and parasite susceptibility? Most research has focused on the proximate mechanisms, such as endocrine or immunological pathways, that are immediately responsible for any one cause.
![marlene zuk animal models and gender marlene zuk animal models and gender](https://www.zoogamy.com/wp-content/uploads/2016/05/4e0fba524c3292d2b07cd8bd0a03b19e7a363854_254x191.jpg)
The persistence of these patterns in the laboratory suggests that the sex difference is not merely due to differences in exposure to parasites, with males and females behaving differently in the field and hence incurring different risks of infection, but to an inherent sex difference in vulnerability. Males usually developed higher parasitemia, with castration removing the sex difference. During the mid-20th century, a virtual cottage industry developed in which investigators experimentally infested laboratory rodents with parasites and documented any resulting sex differences in the prevalence or intensity of the infection that developed. Furthermore, in many free-living mammals, males are more likely than females to harbor parasites or to suffer more intensely from their effects. They concluded, “Being male is now the single largest demographic risk factor for early mortality in developed countries”. Kruger and Nesse compared men's and women's mortality rates for 11 causes of death in men and women from 20 countries, including accidents and homicide as well as infectious and non-infectious diseases, and found that men virtually always die earlier. Fewer women than men died in the 1917–1918 influenza epidemic the differential mortality was not related to World War I, as originally thought, but was global and widespread among ages. Everyone knows that old age homes have more widows than widowers, but the disparity extends far beyond the elderly. Arguments about the weaker sex notwithstanding, there is no contest about the identity of the sicker sex-it is males, almost every time.