Too many topics, too little time

Researchers discover European genetic twist: printer friendly version:
It is particularly surprising that the same genetic element should promote fertility and longevity since most organisms are obliged to follow a strategy either of breeding fast during short lives or of living longer and having fewer children. “Usually people think of there being a trade-off between fertility and longevity,” said Alan Rogers, a population geneticist at the University of Utah.

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ok…. wouldn’t a better explanation of this be that with increased fertility there is a greater chance to spread the gene and thus it should grow as a percentage of population over time?