A DIFFERENCE IN THE METABOLISM OF THE SEXES 59

in the processes of menstruation, gestation, and lactation) the constructive tendency still asserts itself, and a slight access of growth and vitality results to the organism.

DIFFERENCE IN BRAIN WEIGHT FROM TWENTY TO SIXTY YEARS.

Author

Weight Number of women's

of brains brains

Broca (revised list of Wagner),

77 1,244

Welcker, -

258

,247

Peacock (Scotch), -

- 89

,275

Boyd (English), -

370

,221

Thurnam (various),

- 536

,233

Broca (registers),

5i

,195

Bischoff,

272

,227

Broca-Bischoff-Boyd,

693

,211

FROM SIXTY TO

NINETY YEARS

Broca (revised list of Wagner),

32

,203

Welcker, -

99

,175

176

Thurnam (various),

422

,1 / \j ,178

Broca (registers),

85

,111

Bischoff,

50

,157

Difference from man

126

M3

142

133 138 164 141 150

123 125

158 150

Organic development in general, and social structure and function in particular, are conditioned by this fundamental con- trast in the metabolism of the sexes. Sex is, indeed, an expres- sion of this difference, or, more exactly, it is this difference, and in the principle of sex lies the possibility of all higher develop- ment. Asexual organisms never rise above a low type of devel- opment because variation, on which development depends, is furnished only by the union of different organisms. The prin- ciple of sex is, therefore, to be recognized as the beginning of those changes which, controlled by natural selection, end in the development of organs of locomotion, prehension, ingestion, and digestion, fitting the organism increasingly for the struggle for food.

The struggle for food is, however, anti-social, or at best

unsocial, in its beginning, and we must seek the principle of social