New Support 2017: Below copyright notice; above original document of 2016:
Testosterone Controls Human and Great Ape Lifespans
Copyright 2016, James Michael Howard, Fayetteville, Arkansas, U.S.A.
(New Support: "Men with co-occurrence of TD [testosterone deficiency] and abdominal obesity have a higher risk of mortality." (Clin Endocrinol (Oxf). 2017: "Double Trouble: co-occurrence of testosterone deficiency and body fatness associated with all-cause mortality in US men," Lopez, et al.) I explain "all cause mortality and testosterone decline in the last paragraph on this page.)
"CONCLUSION: Our study showed that higher mortality rates were seen among the men who had the most pronounced age-related decline in T, independent of their baseline T levels." (Eur J Endocrinol. 2017: "Individual testosterone decline and future mortality risk in men," Holmboe, et al.))
I suggest the higher levels of testosterone in humans extends our lifespans and is why chimpanzees, and other great apes, exhibit shorter lifespans. Testosterone reduces cellular activity caused by DHEA, therefore, extending the lifespan.
It is my hypothesis that mammals evolved because of evolutionary selection for DHEA. “Hormones in Mammalian Evolution,” Rivista di Biologia / Biology Forum 2001; 94: 177-184. If your library does not subscribe to “Rivista … ,” you may find this at: http://anthropogeny.com/evolution.html . Because of selection for testosterone within mammals, primates were produced along with humans because of increased testosterone with the primates. (“Androgens in Human Evolution,” Rivista di Biologia / Biology Forum 2001; 94: 345-362. If your library does not subscribe to “Rivista … ,” you may find this at: http://anthropogeny.com/Androgens%20in%20Human%20Evolution.htm .)
Briefly, it is my hypothesis that evolution selected dehydroepiandrosterone (DHEA) because it optimizes replication and transcription of DNA, that is, genes. Therefore, DHEA levels affect all tissues and all tissues compete for available DHEA, especially the brain. DHEA naturally begins to decline around the ages of twenty to twenty-five, reaching very low levels in old age. When DHEA is low or decreasing, all tissues / genes are adversely affected. Loss of DHEA is the cause of aging.
Chimpanzee males and females produce much more DHEA and less testosterone than human males and females. This, I suggest, is caused by increased use of DHEA by the brain for growth and development. (The high maternal testosterone of women increases androgen receptors in the brain during fetal brain development which cause the brain to absorb DHEA at the expense of the body. Hence, hominid evolution is characterized by increased brain size and less robust body size with time.) The following chart demonstrates the connection of DHEA levels and lifespans of three primates. I suggest the longer lifespans occur as a result of increased testosterone.
The mechanism, above, reduces available DHEA in humans compared to chimps. Since I think DHEA is directly connected to cell / tissue metabolism, high DHEA would increase cellular division rates which would increase the time to end of lifespan cellular divisions. Since our brains reduce overall available DHEA, not only do our bodies become more gracile, it also decreases the onset of “the time to end of lifespan cellular divisions.”
The foregoing essentially explains why humans outlive chimps. (My explanation of how testosterone and DHEA produce the secular trend is available at www.anthropogeny.com; on the right side, down the page, if interested. The Secular Trend caused by testosterone levels explains all cause mortality, as mentioned in the "new support" section, above.)