62 Life and Letters of Francis Galton
because they express his own strong convictions, but also because they may serve as a warning that we must appeal with caution to the continuity of the palaeontological record
"An apparent ground for the common belief [that evolution proceeds by minute steps only*] is founded on the fact that whenever search is made for intermediate forms between widely divergent varieties, whether they be of plants or of animals, of weapons or utensils, of customs, religion or language, or of any other product of evolution, a long and orderly series can usually be made out, each member of which differs in an almost imperceptible degree from adjacent specimens. But it does not at all follow because these intermediate forms have been found to exist, that they are the very stages that were passed through in the course of evolution. Counter evidence exists in abundance, not only of the appearance of considerable sports, but of their remarkable stability in hereditary transmission. Many of the specimens of intermediate forms may have been unstable varieties, whose descendants had reverted; they might be looked upon as tentative and faltering steps taken along parallel courses of evolution and afterwards retraced. Affiliation from each generation to the next requires to be proved before any apparent line of descent can be accepted as the true one. The history of inventions fully illustrates this view. It is a most common experience that what an inventor knew to be original, and believed to be new, had been invented independently by others many times before, but had never become established. Even when it has new features, the inventor usually finds on consulting lists of patents, that other inventions closely border on his own. Yet we know that inventors often proceed by strides, their ideas originating in some sudden happy thought suggested by a chance occurrence, though their crude ideas may have to be laboriously worked out afterwards. If, however, all the varieties of any machine that had ever been invented, were collected and arranged in a museum in the apparent order of their evolution, each would differ so little from its neighbour as to suggest the fallacious inference that the successive inventors of that machine had progressed by means of a very large number of hardly discernible steps." (pp. 32-3.)
In concluding this chapter Galton apologises for largely using metaphor and analogy, on the ground that he wished to avoid any "entanglements with theory," as no complete theory of inheritance had yet been propounded that met with general acceptance (p. 34). This seems to me to show that Galton looked upon his statistical analysis of inheritance not as a theory of heredity, but as a description of hereditary facts, which it undoubtedly is.
Chapter IV deals with Galton's " ogive curve " (see our pp. 30-3 1) by which he represents a frequency distribution by aid of grades or percentiles. Galton had discussed this manner of representation in numerous earlier papers, and we may refer to Plate II for a graphic representation of his curve. The only novel point in Chapter IV is the suggestion, not very fully worked out, that the scheme of grades or percentiles might be applied to " inexact measures," i.e. to our present so-called " broad categories," and that these may be measures of a great variety of characters including relative professional success. He cites on this latter point Sir James Paget's analysis of the successes of 1000 of his pupils at St Bartholomew's Hospital. Sir James made five classes: (a) Distinguished, (b) Considerable, (c) Moderate, (d) Very limited success, and in the fifth class (e) he put Failures. Galton made the numbers in each 28, 80, 616, 151, and 125 respectively. Among the foremost were the three professors of anatomy in Cambridge, Edinburgh and
* It is a strange but widely spread notion that those who believe in continuous variation of a non-fluctuating character, must ipso facto suppose evolution to proceed by "minute steps." Given a race with mean cephalic index of 75 and a range in index from 65 to 85, there is nothing to prevent by isolation the establishment of a brachycephalic race of cephalic index 82a spring as great as from Englishman to Jew-without transition through all the small intermediate steps from 75 to 82.