Males do not represent two discrete populations, heterosexual and homosexual. The world is not to be divided into sheep and goats. Not all things are… - Alfred Kinsey

The inherent physiologic capacity of an animal to respond to any sufficient stimulus seems, then, the basic explanation of the fact that some individuals respond to stimuli originating in other individuals of their own sex-and it appears to indicate that every individual could so respond if the opportunity offered and one were not conditioned against making such responses. There is no need of hypothesizing peculiar hormonal factors that make certain individuals especially liable to engage in homosexual activity, and we know of no data which prove the existence of hormonal factors (p. 758). There are no sufficient data to show that specific hereditary factors are involved. Theories of childhood attachments to one or the other parent, theories of fixation at some infantile level of sexual development, interpretations of homosexuality as neurotic or psychopathic behavior or moral degeneracy, and other philosophic interpretations are not supported by scientific research, and are contrary to the specific data on our series of female and male histories.

With the right of the scientist to investigate most aspects of the material universe, most persons will agree; but there are some who have questioned the applicability of scientific methods to an investigation of human sexual behavior....It is as though the dietician and biochemist were denied the right to analyze foods and the processes of nutrition, because the cooking and proper serving of food may be rated a fine art, and because the eating of certain foods has been considered a matter for religious regulation. (page 8).

The impression that infra-human mammals more or less confine themselves to heterosexual activities is a distortion of the fact which appears to have originated in a man-made philosophy, rather than in specific observations of mammalian behavior. Biologists and psychologists who have accepted the doctrine that the only natural function of sex is reproduction, have simply ignored the existence of sexual activity which is not reproductive. They have assumed that heterosexual responses are a part of an animal's innate, "instinctive" equipment, and that all other types of sexual activity represent "perversions" of the "normal instincts". Such interpretations are, however, mystical. They do not originate in our knowledge of the physiology of sexual response (Chapter 15), and can be maintained only if one assumes that sexual function is in some fashion divorced from the physiologic processes which control other functions of the animal body.