Random Thoughts

[Angrboda]

The team created this society using around a hundred genetically identical mice. Groups of about 26 two-week-old mice and their mothers were placed in outdoor enclosures in groups that mimicked their natural environment, but had identical "resource zones" with food and shelter available to all. The team tracked the mice over 46 days, measuring how they behaved and various aspects of fitness, like weight.

There was one crucial variable in the setup. In this strain of mouse, males compete with each to form territories and access food, while females don't, says Zipple. "We have this really useful system where we have one sex experience and really intense competition and the other sex does not."

With genetics and environment held largely equal, what's left are "these really micro-contingent experiences," says Zipple.

For example, an individual male mouse might just so happen to win a fight with its identical twin over food. That lucky break would help it become bigger than its twin, setting it up to win the next fight.

Those contingent experiences mattered a lot more for males than females, the researchers reported last week in the journal Science, suggesting that competition magnifies the importance of luck.

For males, "they pretty early on start to diverge into really high quality and low quality males, or males that are gaining access to resources and males that are being excluded from resources," says Michael Sheehan, a biologist at Cornell University and senior author of the study. "We don't see that pattern pan out for the females. They all kind of stay about the same quality the whole time."

Sheehan emphasizes that these results don't mean females aren't getting lucky, too. "They still have good days and bad days," he says. But those good or bad days "don't rack up over time in quite the same way," he says. By the end of the experiment, "lucky" male mice controlled more territory and encountered about five times as many females as lower-quality males, the study found.

https://www.npr.org/sections/shots-healt...-evolution