REINFORCEMENT OF HEREDITARY TENDENCIES.

Dunstan Times, Issue 1235, 30 October 1885, Page 3

REINFORCEMENT OF HEREDITARY TENDENCIES.

Mr Reenan has beau talking, with bis usual eloquence and felicity, in praise of ignorance. “A race,” he said, “gives its flower when it emerges from oblivion. The brilliant intellectual developments proceed from a vast foundation of unconsciousness, I would almost say from vast reservoirs of ignorance.” Would not Mr Renan have been nearer the truth if he had altogether refrained from saying it? Has he not fallen into the common error of supposing that a want of knowledge of letters, or a deficient power of expression, express ignorance? On the other hand, is there not much main truth in his main contention, that his genius, of which with characteristic self-confidence he makes no doubt, is the outcome of long obscure lines of peasants and sailors, whose intellectual sobriety laid the foundations of bis own mind aud life? The faculty of observation trained by generation after generation of tillers of the soil, or toilers of the sea, is transmitted to some fortunate individual who possesses likewise the power of expression. Genius, and much more, therefore, talent, are for Mr Renan no exceptions to the general laws of inheritance. Yet, they are often supposed to be discredited by quoting cases of genius or remarkable talent suddenly appearing in families not previously distinguished. Such facts have been taken up with great glee in certain quarters in order to add weight to deductions unfavourable to the truth of the laws of heredity, founded on a curious misconception of the significance of a oalcuiax tion made by a correspondent of “ Nature.” This ingenious gentleman has been at the pains to calculate how many ancestors every individual in this country has hud | since the Norman Conquest, and arrives at 1 the conclusion that “one is descended from no fewer than sixteen million ancestors ; ” four grandparents,eight great-grandparents, and so on. It has been assumed by some, surely very thoughtless persons, that this is equivalent to saying that in the pedigree of each individual there have bem sixteen million true crosses. There are no figures in existence, or obtainable, to show the amount and degree of intermarriage in the general population ; hut there can be no question that it is now very considerable, and was in former times very much greater. In many isolated districts, intermarrying among the indigenous population has been almost invariable until recent times, and is oven now the rule rather than the exception ; in Scotland, where pedigrees have been preserved for many generations, even by the peasant class, consanguinity can be traced aud is recognised between families which in England would be assumed to be entirely unrelated. The same thing is true to an even more striking degree with the peerage ; pedigrees have been carefully preserved, and intermarriage has been the rule, that is to say, intern marriage in the same class. Taking the grandparents on the second remove, a man would have at the sixth remove 64 ancestors, but there must be very few peers of a creation dating to the beginning of last century who are derived from 64 ancestors in the sixth remove, for the reason that intermarriage would almost certainly come into plav; this would be still more constantly the case in the isolated populations mentioned above. In the hereditary transmission of characteristics there are always two forces in operation, which we may call dilution and reinforcement. It is a matter of eveiy day observation that a tendency may be strengthened or weakened by crossing, and it is upon this fact that breeders of special strains of dogs, cattle, or horses rely in great part, ! the only other influence at their disposal being alteration in food, habitation, or other environment of the young. Exactly the same holds good with the human species. For instance, a man with an hereditary tendency to gout may marry a woman with the same tendency, and their son by his manner of living may develop gout at an early age; that is to say, • the tendency in the father, reinforced by marriage, and again reinforced by habit, develops in the sou with great rapidity ; on the other hand, a man with the gout tendency may marry a woman free fiom that tendency, and, thereby, dilute its force. There are, of course, well-known facts which militate against this view, but they are generally held, wc believe, to be exceptions to the rule. In the case of gout, phthisis, and some other diseases, the exceptions are probably more apparent than real; of the general truth of the law there can be- no question. British Medical Journal,