source of progressive change in the constants-mean values, variabilities corrilations [sic] - which suffice to define an organ or Character or the interrelations of a group of organs or characters, at any stage in any form of life. To demonstrate the existence of such a factor we require to show more than the plausibility of its effectiveness, we need that a numerical measure in the changes in the organic constants shall be obtained from actual statistical data. These data must be of sufficient extent to render the numerical determinations large as compared with their probable errors."
(signed) Karl Pearson
Sep 22 1934