munities where close inter-marriages were practised for two 

 or three generations the mental, moral and physical condi- 

 tion of the people was below normal. This result was likely 

 due to the lack of care in the choice of mates and to the fact 

 that defectives were allowed to marry defectives.^ 



Co-efficient of In-breeding. — Galton's law of Ancestral 

 Heredity has been utilized by some students of pedigrees 

 to ascertain the extent of inbreeding, i.e. the factor of the 

 the number of times that the same animal appears in the 

 pedigree. Pearl has coined the term "Co-efficient of Here- 

 dity" as a precise measure of inbreeding (Bull. 215 Maine 

 Agric. Exp. St. 1913). This co-efficient expresses the 

 relation between the maximum and the actual number of 

 different ancestors, the formula being 



Zn = 100 (Pn + 1- Qn + l) 



Pn -f 1 



In the pedigree of Lodeski (page 148) the formula 

 would work out as follows: 

 Zo = 100 (2 - 2) 



= per cent. 



2 

 Zi = 100 (4—4) 



4 



Z2 = 100 (8-5) 



= per cent. 



= 37^ per cent. 



8 



In the pedigree of Comet (page 149). 

 Zo = per cent. 

 Zi = 100 (4-3) 



= 25 per cent. 



4 



Z, = 100 (8 - 4) 



= 50 per cent. 



8 



(1) — Galton was of the opinion that the Athenians of the period 530- 

 430 B.C. were the most gifted in history, when from 45,000 free- 

 born males surviving the age of fifty came 14 of the greatest 

 men of all time. According to Galton also only 250 men per 

 million of the population of Great Britain became eminent. 

 The Athenians practised endogamy, and marriage with aliens was 

 punishable by law. To this selective inbreeding some would 

 attribute the development of the high gifts of the Athenians of 

 the Age of Pericles. On the other hand, there is much evidence 

 in support of the theory that racial mixing or outbreeding within 

 limits makes for greater ability than inbreeding in the case of 

 isolated countries. 



150 



