KNOWLEDGE YOU CAN USE

KNOWLEDGE YOU CAN USE
Life History Trade-Offs and a Mini-Fountain of Youth: What Is the Relationship Between Reproduction and Longevity?

It’s well documented that there is a trade-off between reproduction and longevity. In a wide variety of animals, decreasing reproductive effort has been shown to increase longevity.

Question 14.11

Q: Does this have any practical applications? Yes: spay or neuter your pet to increase its life span!

Question 14.12

Q: Does this work? Yes! Data from more than 1,000 cat autopsies showed that non-sterilized females lived a mean of 3.0 years, whereas sterilized females lived significantly longer, with a mean life span of 8.2 years. The results for males were similar. (Perhaps the most dramatic example of the reproduction–longevity trade-off is that of the marsupial mouse, Antechinus stuartii, in which castration led to a doubling or even tripling of the usual life span. Similarly, following castration, Pacific salmon lived up to 8 years, double their usual life span.)

Question 14.13

Q: Not that you asked … In a study in the early 1900s of men institutionalized for mental retardation, those who were castrated lived 13 years longer, on average, than non-castrated men, matched for age and intelligence, at the same institution— 69.3 years vs. 55.7 years.

Question 14.14

Q: Does a vasectomy have the same effect as castration? No! The life-extending effect of sterilization occurs only when the ovaries or testes are removed; “tying the tubes” and vasectomy leave the gonads intact. And there is no longevity increase. Why do you think that is the case?

Question 14.15

Q: What is responsible for the trade-off between reproduction and longevity? If it were a question of sterilized individuals living longer simply because they don’t have to expend energy on reproduction, perhaps similar life span increases could be achieved by simply giving animals access to more energy. In practice, however, this doesn’t work (and usually decreases life span). Rather, it seems that a significant part of the “cost” of reproduction, at least in mammals, is an increased incidence of cancer, caused by the higher levels of circulating hormones in “reproductively ready” (that is, fertile and receptive) animals.

Possibilities to think about. The link between maintaining reproductive readiness and reduced longevity has led some researchers to contemplate the design of birth control pills that might have the additional effect of increasing longevity. Stay tuned.

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