Ontogeny

When certain behavior is said to be stereotyped, or the mating of a male rat is called an example of a fixed action pattern, it does not follow that we know how the behavior develops in the individual animal. Male laboratory rats with access to a receptive female begin mating at about thirty five days. Mating requires maturation of the pituitary gonad system and the consequent secretion of substantial amounts of male hormone by the testes. The behavior can be induced precociously by injecting testosteronic. A question that may be asked is: If a male survives to five weeks, will it always make the typical responses to the female regardless of conditions of rearing?

This question can't be answered. Young rats cannot be subjected to all the possible conditions which permit survival, so that we may see whether any of them interfere with the development of rat mating ability. We can observe only the effects of a few selected departures from the usual conditions of upbringing. The mating behavior of both sexes is then found to the notably stable in development. In the most commonly used special environment, the animal has no experience of its own species after weaning: usually, the only living being it encounters between weaning and adulthood are the experimenters. Rats so treated respond appropriately when they meet adults of the opposite sex. Inexperienced male rats, given a choice between cavies, male rats, female rats not in estrus and female rats in estrus, rarely make mistakes.