We should expect many traits to human universal since complex adaptations within a sexually reproducing species need all of their parts, or almost all of their parts, to be universal within the gene pool.

Let's say that you have a complex adaptation with six interdependent parts, and that each of the six genes is independently at ten percent frequency in the population. The chance of assembling a whole working adaptation is literally a million to one; and the average fitness of the genes is tiny, and they will not increase in frequency.

One bird may have slightly smoother feathers than another, but they will both have wings. A single mutation can be possessed by some lucky members of a species, and not by others - but single mutations don't correspond to the sort of complex, powerful machinery that underlies the potency of biology. By the time an adaptation gets to be really sophisticated with dozens of genes supporting its highly refined activity, every member of the species has some version of it - barring single mutations that knock out the whole complex....

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