140 RETROGRESSION 



lengthening of the germ-tract, the increase in the number of cell- 

 generations which occurs when plants are propagated by slips, 

 does not result in an appreciable difference in the number and 

 range of variations, as it would if variability were a fundamental 

 character beyond the control of natural selection, and occurring, 

 therefore, all along the germ-tract. 



231. To sum up: the biometric method, as employed by many 

 of its exponents, suffers from the same defect as the experimental 

 method. Very often no facts other than those revealed by a 

 particular inquiry are taken into account, though many may be 

 available ; and, therefore, inferences from the evidence are left not 

 only isolated, but untested. The science created depends alto- 

 gether on a simple enumeration of instances, not on a knowledge 

 of causes. " But in estimating probabilities, it is not a matter of 

 indifference from which of these two sources we derive our 

 assurance. The probability of events as calculated from their 

 mere frequency in past experience affords a less secure basis for 

 practical guidance than their probability as deduced from an 

 equally accurate knowledge of the frequency of occurrence of 

 their causes." 1 Not seldom in biometric inquiries as in the 

 case of those inquiries about disease and fertility which we 

 have just examined several scores or hundreds of observers 

 and thinkers are employed for years in ascertaining, with a 

 much lesser degree of certainty, that which a single thinker may 

 deduce in two minutes from known and admitted truths. " These 

 are but samples of the errors frequently committed by men who, 

 having made themselves familiar with the difficult formulae which 

 algebra affords for the estimation of chances under suppositions of 

 a complex character, like better to employ those formulae in 

 computing what are the probabilities to a person half informed 

 about a case, than to look out for means of being better informed. 

 Before applying the doctrine of chances to any scientific purpose, 

 the foundation must be laid for an evaluation of the chances, by 

 possessing ourselves of the utmost attainable amount of positive 

 knowledge." 2 Experimental observers, whose evidence we shall 

 consider next, have formulated hypotheses which have seemed 

 fundamentally wrong to biometricians. The latter, or some of 

 them, were induced to employ their method mainly, I believe, in 

 order to demonstrate the erroneousness of the conclusions reached 

 by their opponents. But, if these conclusions are mistaken, and 

 I think there are entirely conclusive grounds for believing that 



1 Mill, Logic, III. xviii. 4 2 Op. cit., III. xviii. 4. 



