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Who has a more varied reproduction rate in modern western societies - men or women? The average rate is the same of course, but I wonder which sex have higher variance - higher variance means that reproduction is more concentrated in some subgroup of given sex so this subgroup transfer their genes at higher rates then averaage rate in whole population. The next question would be 'is that subgroup somehow homogeneous' ?

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Good question. I wouldn't be surprised if the distributions of fecundity (offspring reduced) were multi-modal (have more than one peak). When you just look at sex, the answer is lopsided in more than one way. telegraph.co.uk/news/newstopics/howaboutthat/3685314/… nytimes.com/2007/08/12/weekinreview/12kolata.html –  shigeta Feb 3 '13 at 21:39
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up vote 8 down vote accepted

Sperm are cheaper than eggs

According to Bateman's Principle the males of a species are (typically) more able to produce a greater variance in the number of offspring. This is because generally the males can produce many gametes and achieve many matings whereas females are limited by the number of eggs, resources, and time lost to pregnancy. Therefore, just by simple logic, it would appear likely that males have greater variance in mating success (strong/attractive males would be able to mate with many females while weak/unattractive males would have little to no offspring). See Wikipedia for an introduction to Bateman's Principle. Also see this paper about sexual selection and mating success variance.

An Example

An extreme example of higher variance in male mating success is that seen in lekking species. These species form groups of males called leks where females enter and choose mates. Often one/few males will sire the majority of offspring in the next generation. Fallow deer are one lekking species where males have higher mating success variation than expected by chance.

In Humans

Here is a blog post discussing a paper which showed that males have greater reproductive success variance than females in humans. In the paper see table 1 (Vm:Vf column) which indicates the majority, particularly those close to ancestral type lifestyles, have much greater variance in male reproductive success. Only one measured (Finland) is the reverse pattern.

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nice reference. polygamous cultures are a good illustration (see blog post table 1) of how 'some guys get all the luck'. –  shigeta Feb 4 '13 at 17:48
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