

Sperm Recognize "Brothers," Team Up for Speed - anderzole
http://news.nationalgeographic.com/news/2010/04/100421-glowing-sperm-brothers-cooperation-evolution/

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crazydiamond
(supposedly) In humans, the penis is designed to pull out previously
ejaculated sperm, so only one's own is left inside.

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zackattack
In many animals actually, this is widely believed in ethology

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steve19
Unless these mice participate mating orgies, this seems to me like a rather
useless evolutionary trait.

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nathanmarz
On the contrary, sperm competition occurs frequently in many animal species
(and more often than you'd think in humans - the stats are quite
enlightening). Since this trait increases the chances that your sperm will win
and pass on your genes, it is a very useful evolutionary trait.

More information: <http://en.wikipedia.org/wiki/Sperm_competition>

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jules
The length of this competitive “window” might be as short as 2 or 3 days
(Gomendio & Rolda´n, 1993) or as long as 7 to 9 days (Smith, 1984). Using an
intermediate estimate of 5 days, Baker and Bellis (1995) argued that the
questionnaire data they collected on female sexual behavior indicated that
17.5% of British women “double mated” at some point during the first 50
copulations in their lifetimes.

[http://www.toddkshackelford.com/downloads/Shackelford-
Pound-...](http://www.toddkshackelford.com/downloads/Shackelford-Pound-Goetz-
RGP-2005.pdf)

