We have called the broader, sounder, better balanced, more fully exercised brain "a man's brain," and the narrower, more emotional and personal one "a woman's brain"; whereas the difference is merely that between the world and the house. The absolute relation between any animal's brain and his range of activity is patent to the zoölogist, and simply furnishes the proof of its law of development. The greater the extent and complexity of any creature's business, the greater the mental capacity, of course.
We are familiar with the mental effect of living on small islands--"the insular mind," "insular prejudice" are well known terms. The smaller the island, the more deprived of contact and association with the rest of the world, the greater the insularity of mind. The Englishman is somewhat affected by the size of his country; the Manxman still more, and the dwellers on the lighthouse rock most of all. Our homes are not physically isolated, save on scattered farms and ranches--where the worst results are found; but they are isolated in their interests and industries.
The thought used every day is thought about half a dozen people and their concerns, mainly their personal bodily care and comfort; the mental processes of the woman must needs be intensified in personality as they are limited in range. Hence her greater sensitiveness to all personal events, and that quick variation in attitude so inevitable in a mind whose daily work involves continual and instant change. _Varium et mutabile!_ murmurs the man sagely--"A woman's privilege is to change her mind!" If the nature of his industry were such that he had to change his mind from cooking to cleaning, from cleaning to sewing, from sewing to nursing, from nursing to teaching, and so, backward, forward, crosswise and over again, from morning to night--he too would become adept in the lightning-change act.
The man adopts one business and follows it. He develops special ability, on long lines, in connection with wide interests--and so grows broader and steadier. The distinction is there, but it is not a distinction of sex. This is why the man forgets to mail the letter. He is used to one consecutive train of thought and action. She, used to a varying zigzag horde of little things, can readily accommodate a few more.