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 
aecount 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 3, the grandparents +, and the great grand- 
parents §, 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- 
