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If streamlining makes movement/locomotion quicker and easier, why didn't the apes evolve into life-forms that had streamlined bodies (much like fish)?

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No single advantage drives the evolution of body type. The advantage of streamlining is much greater for aquatic animals as water has a much greateer influence on viability. On land other concerns, defense, physical strength and size are at least as important. Most land animals don't even move quickly. – shigeta Jun 19 '12 at 17:26
This question seems to be based on a fundamentally flawed premise, I don't think it is really answerable due to that. – Mad Scientist Jun 19 '12 at 18:27
I don't think the premise is flawed, as evidenced by @shigeta's comment. I vote to reopen. – kmm Jun 19 '12 at 23:10
I agree - @shigeta's comment does essentially answer the question. The reason we're not as streamlined as fish is that we don't need to be! – Luke Jun 20 '12 at 10:57
" 'cause we're lovers, not fighters!" – shigeta Aug 2 '13 at 16:53
up vote 7 down vote accepted

If streamlining makes movement/locomotion quicker and easier, why didn't the apes evolve into life-forms that had streamlined bodies (much like fish)?

As with everything in Evolutionary Biology, you must ask yourself: Gain vs. Cost?

In your specific case, the Gain is very little. Air isn't nearly as dense as water, so a streamlined form won't show a major benefit unless the organism is traveling very, very quickly. This is why you see it in birds; raptors can travel over 100mph while diving, and at those speeds small changes in drag can mean the difference between dinner and starving. Smaller birds often make very quick turnabouts and changes in direction mid-flight where, again, small changes in efficiency can mean the difference between life and death. The cost was is worth it.

For apes and monkeys, moving very quickly isn't a case of living or dying. That's what we evolved opposable thumbs and prehensile feet(/tails) for. You don't need to run fast when you can climb a tree and simply get away from any predators on the ground. After we came down from the trees permanently, our larger brains allowed us to use tools to fend off predators - which, again, is much simpler than evolving an aerodynamic form that won't make a difference until you're running at the speed of a car.

So, in lieu of becoming a land-shark, we have hands that can use keyboards and minds that can invent the keyboard. Unfortunately, while the gains are many, the costs do include both a very long period of time where humans are helpless without parents, and an absolutely terrible form of locomotion with our upright stance on forward-pointing knees. Though you won't catch Cheetahs digging sewers anytime soon.

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Who says we are not streamlined?

One could easily imagine body structures that would cause much greater drag in air and humans do not have them.

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