Cotton-topped tamarins are small primates with tufts of long white hair on their heads. while studying these creatures, you notice that males with longer hair get more opportunities to mate and father more offspring. to test the hypothesis that having longer hair is adaptive in these males, you should

Determine if the hair length is heritable,

Explanation:

If to check whether the long hair are adaptive in the males or not, one should check whether the trait of long hair is also found in the offspring or not.

If this trait is found in the offspring, also check whether it provide some level of fitness to them or not.

Thus, if this trait is heritable which means that it passes to the offspring, then the trait has adaptive value.  

Hence, by checking whether the hair length is heritable or not, one can test the given hypothesis.

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