I could quote others just as strong as these, in some of which the above phrase “complementary” also appears, while I have not a single case in which my correspondents speak of originally dissimilar characters having become assimilated through identity of nurture.  However, a somewhat exaggerated estimate of dissimilarity may be due to the tendency of relatives to dwell unconsciously on distinctive peculiarities, and to disregard the far more numerous points of likeness that would first attract the notice of a stranger.  Thus in case 11 I find the remark, “Strangers see a strong likeness between them, but none who knows them well can perceive it.”  Instances are common of slight acquaintances mistaking members, and especially daughters of a family, for one another, between whom intimate friends can barely discover a resemblance.  Still, making reasonable allowance for unintentional exaggeration, the impression that all this evidence leaves on the mind is one of some wonder whether nurture can do anything at all, beyond giving instruction and professional training.  It emphatically corroborates and goes far beyond the conclusions to which we had already been driven by the cases of similarity.  In those, the causes of divergence began to act about the period of adult life, when the characters had become somewhat fixed; but here the causes conducive to assimilation began to act from the earliest moment of the existence of the twins, when the disposition was most pliant, and they were continuous until the period of adult life.  There is no escape from the conclusion that nature prevails enormously over nurture when the differences of nurture do not exceed what is commonly to be found among persons of the same rank of society and in the same country.  My fear is, that my evidence may seem to prove too much, and be discredited on that account, as it appears contrary to all experience that nurture should go for so little.  But experience is often fallacious in ascribing great effects to trifling circumstances.  Many a person has amused himself with throwing bits of stick into a tiny brook and watching their progress; how they are arrested, first by one chance obstacle, then by another; and again, how their onward course is facilitated by a combination of circumstances.  He might ascribe much importance to each of these events, and think how largely the destiny of the stick had been governed by a series of trifling accidents.  Nevertheless all the sticks succeed in passing down the current, and in the long-run, they travel at nearly the same rate.  So it is with life, in respect to the several accidents which seem to have had a great effect upon our careers.  The one element, that varies in different individuals, but is constant in each of them, is the natural tendency; it corresponds to the current in the stream, and inevitably asserts itself.