Mothers and Teachers Often Say They Need Another Pair of Eyes

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 they actually would not be beneficial to the fitness of individuals who possessed them. Natural selection always produces the most beneficial traits for a particular organism in a particular environment.
B) Because every time they have arisen before, the individual mutants bearing these traits have been killed by chance events. Chance and natural selection interact.
C) Because these variations have probably never appeared in a healthy human. As tetrapods, we are pretty much stuck with a four-limbed, two-eyed body plan; natural selection can only edit existing variations.
D) 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.