Passage Summary: Because biologists define 'fittest' as 'those who survive,' saying the fittest survive is just saying 'the survivors survive,' which doesn't actually teach us anything.

Conclusion: The claim that the fittest are most likely to survive is uninformative and lacks scientific interest.

Reasoning: Biologists define 'fittest' as 'most likely to survive,' which turns the slogan into a tautology (a statement that is true by definition).

Analysis: The author is making a leap from a linguistic fact (it's a tautology) to a value judgment (it's not scientifically interesting). To find the 'Necessary Assumption,' we need to find the bridge between those two points. The argument assumes that if a statement is true by definition, it cannot provide useful information or scientific insight. If you negate that—if a tautology *could* be scientifically interesting—the author's conclusion that the slogan is useless would crumble.