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How is that not neessary to the argument?

I suppose I may be negating this wrong.

E) Any of bacteria's evolutionary ancestors that lacked a flagellum also lacked a capacity to swim.

I simply put it is not the case before this answer choice. And when you do that, does that not destroy the conclusion of not gaining a survival advantage. If they could swim without a flagellum, then that would be an advantage for survival.

secretad wrote:How is that not neessary to the argument?

I suppose I may be negating this wrong.

E) Any of bacteria's evolutionary ancestors that lacked a flagellum also lacked a capacity to swim.

I simply put it is not the case before this answer choice. And when you do that, does that not destroy the conclusion of not gaining a survival advantage. If they could swim without a flagellum, then that would be an advantage for survival.

I think the correct answer is B, "For parts now incorporated into the flagellum to have aided an organism's survival, they would. have had to help it swim." The author says that because small parts of the flagellum would not have helped it swim, they must have been useless. That's only correct if the only possible contribution could have been through swimming. But what if half a flagellum helped the bacterium sing, or bake, or absorb food? The only way the argument works is if there's nothing flagellums can help with except swimming.

E is incorrect because maybe in those times, bacteria had other ways to swim.

Thanks