The Jokela High School clip was one of about 80 videos posted on the site by Auvinen.

CNN: Finland in mourning after fatal school shooting

"Women's attractiveness functions as a marker or signal of fecundity and gives some indication about health, " Jokela explains.

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"The effect is very small and over several generations, " says Jokela.

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Jokela's study suggests that even as attractive women tend to have more children than their plainer peers, more-attractive men tend to have more daughters than sons.

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Jokela High School was closed for the rest of the week, but some of the 460 students gathered there overnight and into Thursday, crying and lighting candles for the victims.

CNN: Finland in mourning after fatal school shooting

The least-attractive men simply tended to have fewer children than their more-attractive counterparts, but Jokela suggests that might have more to do with the social effects of finding a spouse than evolution.

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