THE ORIGIN OF THE CAT'S RESPONSES TO RATS AND MICE
The question as to what factors determine the behavior of cats toward rats and mice has constituted the problem of several psychological experiments. Since the "normal" (i.e., the usual) reaction of cats to rats and mice is to kill and eat them, the major task of these studies has been to discover the causes of this rodent killing behavior. In popular language the question probably would be phrased, Is rat killing in cats "instinctive"? However, the word "instinct" possesses so many unscientific connotations that it has fallen into disrepute among most psychologists. For this reason a more satisfactory way to state the problem of these experiments is to say that their aim has been to ascertain the respective contributions of native and of acquired factors to the occurrence of rat killing in cats.
The meaning which will be attached to the terms "native response" and "acquired response" in this chapter requires a brief explanation. A response may be regarded as native insofar as it appears through the influence of maturation (i.e., of genetic factors introduced through tissue growth) under the typical environmental conditions (both prenatal and postnatal) of the species. A response which is predominantly native in character is almost certain to appear in every member of a given species when its proper stimulus is presented, provided that the growth and development of the organism (1) have progressed under normal environmental conditions, both before and after birth (as we have said), and (2) have advanced far enough to make possible the reaction in question. Neither the appearance nor the nature of a truly native response is due primarily to modification through previous exposure to the stimulating situation (i.e., to learning). On the other hand, an acquired response is generally understood to be a reaction which is determined primarily by the previous experience of the