Imagine a couple that has hard time conceiving. The guy mines the vagina but there is nothing to extract from it. If the girl gets pregnant then one of those sperms means that made it through, much like someone mining a successful block. That is prove of work and the guy usually marries the girl to seal the deal.
After the child is born and grows up they usually take care of the parents. This was more applicable in the old times when a family had many children so that they could work in the fields. We can say that the parent is staking his children in order to get rewards from them. They represent the family and all work for a common goal. That is PoS.
So more or less the concept of PoW and PoS is drawn from basic biological functions. We just take those concepts and try to apply it to other parts of our life in order to rationalize our economic endeavors.