THE METHODS AND SCOPE OF GENETICS 5 
observations in order to test their general validity. The weakness of 
the method in biology lies in the lack of rigid experimental control over 
the phenomena which are under observation, and also in the fact that, 
often it is either very difficult or impossible to subject to experimental 
verification the principles or laws which have been thus formulated. For 
this reason, the method of observation as a means of formulating prin- 
ciples and laws must constantly be subjected to rigid scrutiny, lest unde- 
tected fallacies lead to the acceptance of conclusions which actually have 
no significance from a biological standpoint. 
But although the observational method has very definite limitations in 
the determination of genetic principles, nevertheless it has been the chief 
method of investigation in the formulation of some of the most stimu- 
lating theories of biological science. The marshalling of evidence by 
Darwin in support of the evolution theory depended almost entirely on an 
application of this mode of research to a vast array of more or less iso- 
lated cases. The mass of evidence, which he accumulated in order to 
demonstrate that natural selection by favoring the “survival of the 
fittest,’’? to use Spencer’s phrase, results in evolutionary progress in suc- 
ceeding generations, will ever stand as a monument to his masterly skill 
in observation and interpretation. 
In addition to its utilization in the development of the evolution 
theory, the observational method has been employed widely in the field 
more strictly included in genetics. Sir Francis Galton employed a 
refined type of the observational method in his study of heredity. His 
object was to establish a law of organic resemblance within a single 
species, distinctly a problem of genetics. In order to do this he employed 
a system of more exact observation based upon accurate determinations 
in a large number of instances and mathematical reduction of the data 
thus collected. This system has since undergone notable development, 
particularly at the hands of Karl Pearson, and, as biometry, it is often 
accorded recognition as a distinct branch of biology. As one of the re- 
sults of his studies, Galton announced the law of ancestral inheritance 
which states that on an average each parent contributes one-quarter or 
0.52, each grandparent one-sixteenth or 0.5%, and so on to the total 
heritage of the individual, which equals 1.0. The other notable result 
of these studies, the law of filial regression states essentially that on the 
average any deviation from racial type is transmitted to the offspring in a 
lessened degree, so that, in general, offspring differ less from the type 
of the race than their parents; specifically they exhibit a deviation from 
the racial mean only two-thirds as great as the parents. 
Mere observation, be it ever so precise, is subject to very decided 
limitations when employed as a method of analyzing the general problems 
of evolution and heredity. To be convinced of this, one need only con- 
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