K. Pkarson 215 



relative constancy depends laiguly on the exieiil to whieh it has appeaied in the 

 ancestry, and ono by onc black, bay, cliestnut, grey mii.st be dismissed by the 

 Meudolian as iieither "lecussivc" nur "dominant," but as marking " pernianent 

 and incorrigible niongrols." Tho sanie reniark applios to coat-colour in liounds, 

 black niust be the mark of incorrigible niongrelisin for it is neithor recessive 

 nor dominant. It is the same with red and white, no coluur in the parents gives 

 for every case consistent otfspring. 



Nor again do we find that two black-eyed human beings nor two blue-eyed 

 human beings mated togethcr give any sign of the dominance of one or other 

 of these extremes ; any morc tlum do intermediate tints to which the description 

 of " incorrigible mougrelism " niay by sonie be applied. It will be clear that 

 for man (and this applies not only to eye-colour, but to hair-colour, and to a 

 whole .series of measurable characters * of which we have in each case more than 

 a thousand instances in our Family Recoi'ds), for hoi-ses in coat-colour, and for 

 dogs in coat-colour f uothiug approaching Mendelian principles holds. We have 

 therefore to classify large portions of the animal kingdom as exceptions to Mendels 

 Laws, — and these are cases where the evidence is not based on five or ten in- 

 dividnal crosses followed perhaps for two or at most three generations — but 

 on lüOO's of crosses, and where the pedigree has been or can be investigated for 

 some of the material for five to teu generations. What inay happen in the 

 case of plant hybrids, I am not able from personal Observation to assert, but there 

 is enough weight of evidence here to make one pause before one is prepared to 

 admit that Mendel, or his followers, can change each conception of life in which 

 heredity bears a part ! 



(3) Taking our stand then on the observed fact that a knowledge neither of 

 parents nor of the whole ancestry will enable us to predict with certainty in a 

 variety of important cases the character of the individual oßspring we ask : What 

 is the correct method of dealing with the problem of heredity in such cases ? The 

 causes A, B, C, D, E, ... which we have as yet succeeded in isolating and defining 

 are not always followed by the effect A', but by any one of the cffects U, V, W, 

 X, Y. We are therefore not dealing with causation but correlation, and there is 

 therefore only one method of procedure possible ; we niust collect statistics of the 

 freipiency with which U, V, W, X, Y, Z respcctively follow on A, B, G, D, E.... 

 From these statistics we kuow the most probable result of the causes A, B, C, 

 D, E and the frequency of each deviation from this most probable result. The 

 recognition that in the existing state of our knowledge the true method of 

 approaching the problem of heredity is from the Statistical side, and that the 

 most that we can hope at present to do is to give the probable character of 

 the offspring of a given ancestry, is one of the great Services of Francis Galton to 

 biomotry. 



* Mendelianism fails also for skin-colour in crosses between tlie black aud white races of man. 

 t Other characters in pedigree stock are being taken into eousiJeration at present. 



