Why do organisms have some traits that do not appear to have any evolutionary advantage?
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$\begingroup$ Also, let me know if this question should be merged should be merged with this thread: biology.stackexchange.com/questions/35532/…. They are fairly similar. $\endgroup$– C_Z_Commented Jun 27, 2015 at 2:52
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$\begingroup$ You could have answered there itself. $\endgroup$– WYSIWYGCommented Jun 27, 2015 at 6:27
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2$\begingroup$ @WYSIWYG Fair enough, the reason I didn't is because I figured the question "Why didn't X trait evolve if it would be advantageous" and "Why did X trait evolve if it isn't advantageous" are different enough to warrant two separate questions. $\endgroup$– C_Z_Commented Jun 27, 2015 at 15:42
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1 Answer
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There are many reasons why an organism might have a trait that does not appear to be beneficial.
The trait is actually advantageous even if it does not appear to be.
The trait is a byproduct of another trait, which is beneficial. Not all traits are the product of direct selection; traits that are byproducts of other traits are known as "spandrels", a trait coined by Stephen J. Gould and Richard Lewontin
The trait was fixed by some process other than natural selection, such as genetic drift. Genetic drift can fix traits that are neutral or even evolutionarily disadvantageous.
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$\begingroup$ Also, the trait may have been beneficial at some point but no longer is. See: biology.stackexchange.com/questions/34466/… $\endgroup$ Commented Jun 27, 2015 at 4:17