It has already been noted as a general rule throughout nature that the male seeks the female and physicians generally believe that men are sexually more active than women,[58] though woman's need of reproduction is greater,[59] and celibacy unquestionably impresses the character of women more deeply than that of man. Additional evidence of the greater sexual activity of man is furnished by the overwhelmingly large proportion of the various forms of sexual perversion reported by psychiatrists in the male sex. Pathological variations do not become fixed in the species, because of their disadvantageous nature, but their excess in the male is, as we have seen in the case of variations which have become fixed, an expression of the more energetic somatic habit of the male. A very noticeable expression of the anabolism of woman is her tendency to put on fat. "Women, as a class, show a greater tendency to put on fat than men, and the tendency is particularly well marked at puberty, when some girls become phenomenally stout."[60] The distinctive beauty of the female form is due to the storing of adipose tissue, and the form even of very slender women is gracefully rounded in comparison with that of man. Bischoff found the following relation between muscle and fat in a man of 33, a woman of 22, and a boy of 16, all of whom died accidentally and in good physical condition: Man Woman Boy Muscle 41.18 35.8 44.2 Fat 18.2 28.2 13.9 The steatopyga of the women of some races and the accumulation of adipose tissue late in life are quasi-pathological expressions of this tendency.