NEED OF EXPERIMENTAL STUDY 537 
Active and Latent Genes. — Not all of the genes inherited 
manifest themselves, for many lie dormant and consequently 
cause no corresponding characters to develop. Sometimes they 
lie dormant for a generation or more and then become active. 
On this account offspring may have ancestral characters which 
the parents did not have. Certain genes for male characters 
are always latent in females. Thus a mother may transmit to 
her son genes for a beard like her father’s, although she develops 
no beard herself. It is obvious that one cannot accurately judge 
the constitution of a plant or animal by the characters present, 
for judgment based upon external appearances takes no account 
of the latent genes. Further breeding is necessary to determine 
‘hese. Latent genes becoming active is, therefore, one of the 
reasons why offspring differ from their parents. 
Importance of the Study of Heredity. — The study of her- 
edity occupies an important position among the sciences. The 
study of heredity has for its aim the discovery of the laws of 
heredity, and a knowledge of these laws is essential in many 
lines of work. The improvement of our crop plants and domes- 
tic animals through breeding depends upon the laws of heredity. 
The science of sociology and all sciences dealing with the physical, 
moral, and spiritual welfare of humanity are more or less con- 
cerned with the laws of heredity. Even in the realm of medi- 
cine the laws of heredity are taken into account. 
Experimental Study of Heredity 
Need of Experimental Study. — In the discussion of evolution 
it was shown that the application of the experimental method 
to the study of evolution has added much to our knowledge 
of this subject. We had no definite knowledge of the kinds of 
variations and their relation to natural selection until they 
were studied by the experimental method. In the study of 
heredity the experimental method is as essential as in the study 
of evolution. Heredity is so apparent in both plants and ani- 
mals that we are all convinced of its reality. That children 
resemble their parents in habits, disposition, color of eyes and 
hair, and other features are so noticeable that they are matters 
of common observations. Casual observations, however, fall 
short of giving us a knowledge of the laws of heredity. The 
