Mothers and teachers have often said they need another pair of eyes on the backs of their heads.?

Mothers and teachers have often said 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?