Английский словарь американских идиом - survival of the fittest

{n. phr.} The staying alive or in action of the best prepared; often: idea that those living things best able to adjust to life survive and those unable to adjust die out. * /Life in the old West was often a case of survival of the fittest./ * /With changes in the world's climate, dinosaurs died but many smaller animals lived on. It was survival of the fittest./ * /On the 50-mile hike it was survival of the fittest; only 12 out of 25 Scouts finished./