Wednesday, April 12, 2006

Sex differences in senescence reconsidered

A reassessment of sexual dimorphism in human senescence: Theory, evidence, and causation
Brent M. Graves, Mac Strand, Alec R. Lindsay, AmJHumBio (2006) 18:161- 168

Abstract: Age-specific mortality rates of men are higher than those of women, and men have shorter average life spans than women. This has been interpreted as evidence of sexual dimorphism in rates of senescence. However, because mortality can be caused by numerous factors in addition to senescence, higher mortality rates do not necessarily indicate more rapid senescence. In this paper, we (1) emphasize the necessity of decoupling mortality and senescence when considering sexual dimorphism in senescence, (2) present a theoretical framework for the hypothesis that selection affects senescence in human males and females differently due to different life history characteristics, (3) consider phenotypic evidence from the literature that human males show a later onset of senescence than human females, despite exhibiting higher mortality rates, and (4) discuss the potential roles of mutation accumulation and antagonistic pleiotropy in the evolution of sexual dimorphism in senescence. Am. J. Hum. Biol. 18:161-168, 2006. © 2006 Wiley-Liss, Inc.

Who gets older and weaker faster? Men or women? Depending on what you're looking at, the evidence seems very mixed. This paper calls for the need to seperate mortality and senescence. The authors state that even though male life span is shorter, men actually senesce slower. They cite evidence from a variety of studies. This literature review is far from complete. I have reviewed this literature (sports physiology, physical activity levels, gerontology) in the last few months, and have had a hard time finding consistent sex differences in senescence.
The authors discuss the evolutionary mechanisms underlying sexual dimorphism in senescence and conclude that it must evolve via the antagonistic pleiotropy process, rather than the mutation accumulation process. They state that:
"This conclusion illustrates our perspective that the evolution of sexual dimorphism in senescence should be considered in different ways from the evolution of senescence itself."

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