Question

Mothers and teachers often say they need another pair of eyes on the backs of their heads. And another pair of hands would come in handy in many situations. You can imagine that these traits would have been advantageous to our early hunter-gatherer ancestors as well. According to sound evolutionary reasoning, what is the most likely explanation for why humans do not have these traits?
A. Because every time they have arisen before, the individual mutants bearing these traits have been killed by chance events. Chance and natural selectioninteract.
B. Because humans are a relatively young species. If we stick around and adapt for long enough, it is inevitable that the required adaptations will arise.
C. Because these variations have probably never appeared in a healthy human. As tetrapods, we are pretty much stuck with a four­limbed, two­eyed bodyplan; natural selection can only edit existing variations.
D. Because they actually would not be beneficial to the fitness of individuals who possessed them. Natural selection always produces the most beneficialtraits for a particular organism in a particular environment.

Answer 1

Answer:

C

Explanation:

Natural selection depends on variation of a trait and ability to survive and reproduce.

A variation has to occur in order for evolution to occur.

In this case. Humans do not have extra pair of eyes and hands because there is a probability these variations never occurred in a healthy human.  

Therefore as tetrapods we are stuck with four limbs and two eyed body plan.