Monday, November 5, 2012
A Theory of Human Longevity
Humans have an incredibly maximum potential life expectancy especially in comparison with our primate ancestors and our hunter-gatherer counterparts. The decline in mortality rate can be attributed to improvements in technology. Currently, a 65 year-old Japanese man is 200 times less likely to die than his hunter-gatherer counterpart. The Japanese man has an expected annual probability of death of 0.8%, compared to the 65 year-old hunter-gatherer with an expected annual probability of death of 5.3%.
Technology does not explain why humans posses a much higher maximum potential human lifespan. Today, because of our long life expectancy we are able to postpone aging and its detriments. We are able to pass down our genes before the effects of old age set in. This is the result of oocyte depletion, but oocyte depletion happens before the other defects of age occur. The short-finned pilot whale and the Asian elephant are the only other known species that experience the same post-reproductive phenomenon; In fact the average American woman lives 79.2 years, 30 of which are post reproductive.
A recent study modeled the Grandmother Hypothesis and found that even a small contribution of gradmothering was attributed to longer potential lifespan. In the study I found they assumed that only women above the age of 45 could be grandmother. At age two the study assumed that children are able to leave mothers for their grandmothers because they have gone through the nursing period, and at 3 the mother is able to have a second child. Then at 8.2 children reach the age of independence. So the grandmother cares for the child for 6.2 years. Under the assumptions of this study, eligible grandmothers initially make up less than 1% of females, but that proportion steadily increases to 43%. Showing the dramatic effect grandmothering has on increasing longevity
The reasoning for this is that grandmothers are able to supply food that the child cannot get himself; they also allow the mother to reproduce before her first child’s age of independence. Grandmothers are investing in their grandchildren’s lives to ensure the success of their genes. This gives credence to why menopause may have been selected.
This study does not disprove other theories as to why humans have a longer lifespan, but it is a narrow study that shows the benefits that the role of a grandmother has in evolution.
•Brooks, Rob. "Is Human Longevity Due to Grandmothers or Older Fathers?" The Huffington Post. TheHuffingtonPost.com, 31 Oct. 2012. Web. 05 Nov. 2012. <http://www.huffingtonpost.com/rob-brooks/why-do-humans-tend-to-liv_b_2046127.html>.
•Burger, Oksar, Annette Baudisch, and James W. Vaupel. "Human Mortality Improvement in Evolutionary Context." Proceedings of the National Academy of Science of the United States of America 109.44 (2012): n. pag. Print.
•Kim, Peter S., James E. Coxworth, and Kristen Hawkes. "Increased Longevity Evolves from Grandmothering." Proceedings of the Royal Society Biological Sciences (2012): n. pag. Increased Longevity Evolves from Grandmothering. Web. 05 Nov. 2012. <http://rspb.royalsocietypublishing.org/content/early/2012/10/18/rspb.2012.1751.full>.
•Kuhle, B. "An Evolutionary Perspective on the Origin and Ontogeny of Menopause." Maturitas 57.4 (2007): 329-37. Print.