EVOLUTION, HEREDITY, EUGENICS 519 



Francis Galton in 1889 seemed to some to satisfy the theoretical 

 requirements. 



Gallon's Law of Ancestral Inheritance in essence was that the 

 two parents between them contribute ^ of each inherited faculty, 

 the grandparents together contribute ^, the great grandparents 

 1/8. (The individual, i = ^ plus yi plus 1/8 plus 1/16 and so on.) 

 Since this theory does not apply to individual cases and takes no 

 account of prepotencies or the domination of the characters of one 

 parent, it is not accepted. 



Gregor Mendel (i 822-1 884). — The Austrian monk, Gregor 

 Mendel, having worked for eight years with bees and garden peas, 

 in 1865 published an account of his work in the Proceedings of the 

 Natural History Society of Brunn, Moravia, but this was over- 

 looked until 1900 when De Vries, Correns and Tschermak, inde- 

 pendently arriving at similar conclusions, brought the earlier work 

 to light. In 1902, Bateson, an Englishman, pointed out its great 

 importance and since then we have been much interested in experi- 

 ments which seem to substantiate the early conclusions and carry 

 the work on to a point where it is being applied in practical work 

 with cattle, poultry and plants. 



MendeFs First Law: The Law of Dominance. — When mating 

 occurs between two animals or plants unlike with reference to a 

 single unit character the " hybrid-character resembles one of the 

 parent forms so closely that the other either escapes observation 

 completely or cannot be detected with certainty." The character 

 of one parent only thus exhibited is called " dominant " while the 

 other latent character is called " recessive." 



If the dominant determiner is absent, and the recessive deter- 

 miner is duplicated, the recessive character is exhibited. Thus we 

 may have a " dominance of recessiveness." 



When the hybrid offspring of such a cross are in turn crossed 

 with each other, it is found that 25 per cent will be like the dominant 

 grandparent, 25 per cent like the recessive grandparent, and 50 

 per cent like the parents that resemble the dominant grandparent. 



We have therefore by crossing two DR's: yi DD plus yi DR 



plus X RR. 



When a pure dominant is crossed with a mixed dominant 

 recessive, the offspring will all show the dominant character, though 

 of course one-half of them are DR's. DD X DR equals 2 DD plus 

 2 D (R). The DD's are pure and the D (R) is like any other hybrid 



