Allan Kardec. The book of spirits (№ 397199)

Question: There are people who, from the fact that animals eventually leave their young conclude that, if family ties are nothing more than the result of social mores, not the law of nature. We have to think about it?
Answer: a person a different fate than animals. What, therefore, always want to liken him to them?! He, in addition to physical needs, there is yet another property: it is a necessity of progress. Progress requires social connections and family ties strengthen these ties. This is why a person's family ties - nature's law. God wants people to learn in their brotherly love to each other.