318 PROF. K. PEARSON ON THE MATHEMATICAL TBEORY OF EVOLUTION. 
The two hypotheses with which we have dealt give practically the two extremes ; 
observation and experiment are perfectly able to determine between them, or to settle 
whether an intermediate theory is necessary which will give a progression, but a 
slower progression, to the focus of regression. There are many ways in which 
analysis can put on the brake, if it be really needful. 
At present, all this memoir proposes is to show that such subjects as inheritance, 
regression, assortative mating and panmixia, are capable of perfectly direct quantita¬ 
tive treatment, and that such treatment, and not somewhat vague discussion of 
individual instances or of metaphysical possibilities, is what alone can settle the chief 
problems of evolution. What is wanted is a wide extension of the experimental and 
statistical work of Mr. Francis Galton and Professor AVeldon. Such numbers as 
appear in this memoir must be looked upon as illustrative and tentative only. I 
hope later to publish, for a very limited field, namely, skull measurements in man, 
a more complete numerical study with mathematical discussion of variation and 
correlation. 
