58 Life and Letters of Francis Galton
Natural Inheritance may be antiquated now, but in the history of science it will be ever memorable as marking a new epoch, and planting the seed from which sprang a new calculus, as powerful as any branch of the old analysis, and valuable in just as many fields of scientific research.
In its application to inheritance the work suffers from the same misinterpretation of "regression" that I have several times referred to, namely making the regression of offspring of given parentage a great biological law, when it really arises from the clubbing together of all offspring of given parentage without regard to their earlier ancestry. Given selected parentage and grandparentage alone, then with our present numerical values of the multiple correlation constants, it seems highly probable that the progeny of selected offspring would progress rather than regress on their parents and grandparents. In other words, given a line in which by chance or artificial selection there has been marked ancestry for two or three generations, and which is then isolated or inbred, there is reason to believe it would progress even beyond its ancestry rather than regress. Statistical investigations of heredity since 1889 seem to indicate a progressive evolution in selected lines, rather than a general regression to a population mean`. That would only arise from the far too frequent mating with mediocrity or worse than mediocrity. If G s misinterpretation of regression runs through Natural Inheritance,
d makes him appeal to " sports " for evolutionary changes ; if the reader is puzzled to know why Galton should study " variations proper," which according to him have no permanent value for evolution ; still the book is a great book, for it applies a wholly new calculus--if one still in its infancyto an important biological problem.
I think, however, that Galton fully grasped how much more important was his method than its special application. He writes that his conclusions "depend on ideas that must first be well comprehended, which are now novel to the large
majority of readers and unfamiliar to all. But those who care to brace themselves to a sustained effort, need not feel much regret that the road to be travelled over is indirect, and does not admit of being mapped beforehand in a way that they can clearly understand. It is full of
interest of its own. It familiarises us with the measurement of variability, and with curious laws of chance that apply to a vast diversity of social subjects. This part of the inquiry may be said to run along a road on a high level, that affords wide views in unexpected directions, and from which easy descents may be made to totally different goals to those we have now to reach. I have a great subject to write upon, but feel keenly my literary incapacity to make it easily intelligible without sacrificing accuracy and thoroughness." (Chapter i, pp. 2-3.)
Galton in his Introductory Chapter states that there are three problems with which he will be principally concerned. The first problem is to determine how a population can, under the laws of heredity, keep stable from generation to generation. The second problem regards the average share contributed to the character in the offspring by each ancestor severally. The third problem is to measure numerically the nearness of kinship in
* There has always been this element of truth in Johansen's theory of "pure lines," that selected lines do not regress if they are isolated or inbred. The doubtful dogma of that theory is that exceptional members of a "pure line" are only "fluctuating variations," and so no further selection is of any value within a "pure line."