A man who does not think for himself does not think at all. The Soul of Man Under Socialism

If people did not love one another, I really don't see what use there would be in having any spring. Les Misérables

In particular, while natural selection favors both males and females that leave many offspring, the best strategy for doing so may be different for fathers and mothers. That generates a built-in conflict between the parents, a conclusion that all too many humans don’t need scientists to reveal to them. We make jokes about the battle of the sexes, but the battle is neither a joke nor an aberrant accident of how individual fathers or mothers behave on particular occasions. It is indeed perfectly true that behavior that is in a male’s genetic interests may not necessarily be in the interests of his female co-parent, and vice versa. That cruel fact is one of the fundamental causes of human misery. Why Is Sex Fun?: The Evolution of Human Sexuality

For nothing is more democratic than logic; it is no respecter of persons and makes no distinction between crooked and straight noses. The Gay Science