538 HEREDITY 



discovery of the laws of heredity requires carefully planned and 

 systematic work. One must obtain a more or less accurate 

 knowledge of the history of the parents, control the breeding 

 so as to know the exact parents of the offspring, carefully study 

 each individual of the offspring so as to discover the hereditary 

 relationship between parents and offspring and between the 

 different individuals of the offspring. One must also take into 

 account the conditions which affect the plants or animals of the 

 experiment. Carefully recorded facts obtained by experimental 

 study involving a number of generations and various kinds of 

 plants and animals afford a basis for conclusions concerning the 

 laws of heredity. The experimental study of heredity as just 

 described is known as genetics, a subject in its^ infancy but one 

 of the most popular and most promising of the sciences. 



Biometry. Before the experimental method of studying 

 heredity came into common use, the statistical method was 

 employed. The investigators who study heredity by the sta- 

 tistical method of recording data are called biometricians. In- 

 stead of dealing with the variations of single individuals, they 

 deal with the average variations of a mass of individuals or 

 populations. It is a method of discovering how masses of 

 individuals behave through a series of generations, and not a 

 method of discovering how individuals behave. For example, 

 they determine whether or not the average yield, average 

 height, or average weight of a population is remaining constant 

 or shifting, and such information is often valuable. By keeping 

 a record of the average yield per acre of different strains of 

 Wheat for a number of years, the strain yielding best can be 

 determined. By such records one can also detemine whether 

 or not newly introduced strains or varieties hold up in yield. 



The biometricians formulated some laws of heredity. Francis 

 Galton, who was one of the foremost of the biometricians, formu- 

 lated a law of heredity and announced it in 1897. This law 

 states that to the total heritage of the offspring the parents on 

 an average contribute J, the grandparents J, and the great grand- 

 parents J, and so on, the total heritage being taken as unity. 



The objection to the method employed by the biometricians 

 is that it does not pay enough attention to the variations of 

 individuals. A mass of individuals, such as a field of Wheat 

 or Corn grown from the purest market seed, is a mixture of in- 



