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7LeagueBoots t1_jac0s19 wrote

No, it needs to be not worse than. Better is nice, but it's not necessary.

The selection process is often not about gaining an advantage, it's about not having a disadvantage. 'As good as' is usually just fine for evolution.

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owiseone23 t1_jac139q wrote

it's not uncommon for traits to evolve across "fitness valleys". That is, a trait with positive fitness that requires multiple generations to evolve with intermediate generations having negative fitness.

With a large population and a lot of time, random variation makes it possible to evolve across fitness valleys.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2711507/

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