Now we come to human beings, and see how different they are! They have no regular mating season, and while there is a certain amount of instinct in men and women which tends to bring them together, the sex impulse among highly developed people is far more the result of their feeling of love for each other than mere animal instinct alone. Many of the animals make no choice at all in their mating. Any near-by female will do for the male. But among some of the higher animals the male has a special instinct for a certain female, and the female will not tolerate any but a certain male. Most of the animals have different mates every season, though there are a few kinds where the male and female, once having mated, remain mates for years, sometimes even for life. But it is _only human beings_ whose mating is what we call “falling in love,” and that is an experience far beyond anything that the animals know. It means that a man and a woman feel that they _belong_ to each other in a way that they belong to no one else; it makes them wonderfully happy to be together; they find they want to live together, work together, play together, and to have children together, that is, to marry each other; and their dream is to be happy together all their lives. Sometimes the dream does not come true, and there is much failure and unhappiness, but just the same people go right on trying to make it a success, because it is what they care most for. The sex attraction is the strongest feeling that human beings know, and unlike the animals, it is far more than a mere sensation of the body. It takes in the emotions and the mind and the soul, and that is why our happiness is so dependent upon it.