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. 30-31) 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 fore- 

 most 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 82 — 

 a spring as great as from Englishman to Jew — without transition through all the small inter- 

 mediate steps from 75 to 82. 



