In short, there is no possible room for argument as to whether each particular character--with all its possibilities, intellectual or emotional--is not predetermined by the character of nervous structure, slowly evolved by millions of billions of experiences in the past. As the differences in the ancestral sums of experiences, so the differences in the psychical life. Varying enormously in races so widely removed as English and Japanese, it is impossible to believe that any feeling in one race is exactly parallelled by any feeling in the other. It is equally impossible to think that the feelings of a Japanese child can be the same as those of an English child born in Japan. Amazing physical proof to the contrary would be afforded by a comparative study of the two nervous structures.
To say, therefore, that the sight of a toy--adjusted exactly by the experience of the race to the experience of the individual--produces on the mind of a Japanese child the same impression it would produce on the mind of an English child born in Japan and brought up by Japanese only, would be to deny all our modern knowledge of biology, psychology, and even physiology. The pleasure of the Japanese child in its toy is the pleasure of the dead.
DEAR CHAMBERLAIN,--"The law of heredity is unlimited in its application" (Spencer, "Biology," vol. I, chapter "Heredity"). "Some naturalists seem to entertain a vague belief [like yours?] that the law of heredity applies only to main characters of structure, and not to details; or that though it applies to such details as constitute differences of species, it does not apply to smaller details. The circumstance that the tendency to repetition is in a slight degree qualified by the tendency to variation (which ... is but an indirect result of the tendency to repetition) leads some to doubt whether heredity is unlimited. A careful weighing of the evidence ... will remove the ground for this skepticism." ("Biology," vol. I, p. 239.)
Your statement that the "weak person will always remain weak," but that "the manifestations of his weakness will surely depend on the nature of the obstacles in his way," is a proof that you do not perceive the full reach of the explanation. The manifestations of weakness may be evoked by obstacles, but the nature of those manifestations cannot possibly have anything in common with the nature of the obstacles. The weakness being hereditary, the nature of the obstacle cannot change it.