258 THE PRESENT IMPORTANCE OF SCIENCE 



says you may expect to live until you are sixty-four. This 

 is well so far as it goes. It is comforting to feel one has that 

 much lease on life, even though his life is almost half spent. 

 And this knowledge does very well for life insurance com- 

 panies, since it can be applied to thousands of policy holders 

 with a degree of certainty that places the whole superstruc- 

 ture of the insurance business upon a stable foundation. 

 In your particular case, however, this kind of certainty is 

 not satisfying, since it can tell you nothing of your own or 

 any other individual's duration of life. Though you die 

 to-morrow or live to be a hundred, your life merely counts 

 as one item in the statistics upon which such tables are 

 based. 



The insurance tables, therefore, allow us to make proph- 

 ecies for populations, but not for individuals, and this is essen- 

 tially the nature of Galton's law of heredity. It attempts to 

 say what will be the inheritance on the average, but leaves us 

 in the dark as to what will happen in the individual case. 

 If, on the other hand, the life insurance company were able, 

 after looking you over, to say that, barring death by acci- 

 dent, you would become an octogenarian, or to say that in- 

 ability to resist disease would cut you off at forty, then we 

 should have the kind of prophecy it is possible to make in 

 cases of Mendelian inheritance which have been thoroughly 

 investigated. For here, we can, by proper testing of the 

 individual, foretell the characters he will transmit to his 

 descendants. Galton's law is then of value as a statistical 

 statement, but as a guide in the fundamental analysis of 

 heredity it can scarce be compared with the law of Mendel. 



The discovery of the Mendelian phenomena, like most im- 

 portant advances in the science of biology, was not the re- 

 sult of any feverish search for utilitarian values. Mendel's 

 interests were along theoretical lines. The account of his 

 experiments remained buried hi an obscure publication, 

 until after the same phenomena had been rediscovered by 

 later workers about 1900. And now, less than a quarter of 



