波兰性学家曾做过这样一种动物试验，把一对猴子单独关在一只笼子里观察。开始时，他们频繁地互相捋毛（捋毛是彼此亲热的表示），频繁进行交配。而过了一段时间，他们互相捋毛和交配的次数明显减少。再过一段时间，他们彼此不再捋毛，也不再交配，雄猴子甚至顾不上再看雌猴子 Polish sexologists have done such an animal experiment, a pair of monkeys in a separate cage to observe. In the beginning, they frequently bewildered each other (beard is mutually affectionate expression), frequent mating. After a while, the number of beardings and mating with each other was significantly reduced. Some time later, they no longer betray each other, and no longer mate, male monkeys even attend to look at the female monkey