systematist frankly makes no attempt whatever to describe or define a particular species « as a species » (i. e., as a « group » of animals) in terms of its (the species') qualities. Instead he describes one individual animal belonging to this species; affirms either expressly or tacitly that all other individuals belonging to the species are « about » or « generally » like the individual described, and then calls the net result the definition or description of the species. But now sorely this is not a description of the « species » at all. An adequate description of the species will be one which takes account of its peculiarities « as a unit », and indicates how it as a unit or as a whole is distinguished from other similar groups. In making this statement there is, of course, no implication that the facts set forth by the systematist are not desirable and useful. But something more is needed to gain a well-rounded adequate idea of the group, whether species, variety or any other.
It is a particular and fundamental point of significance of biometry for biology that it offers an adequate solution of just this problem of the description of the group as whole or a unit in terms, not of its component individuals, but of its own attributes and qualities. The biometrical constants (mean, standard deviation, coefficient of variation, etc.) are constants characteristic of the « group » as such, and not of any particular individual or individuals in it. So, further, the shape of the variation curve for a particular group of organisms is something definitely characteristic for the group.
The fact that in statistical methods we have the means of accurately describing the attributes of groups of organisms as groups affords an opportunity of investigating why groups (i. e., species, varieties, etc.) come to have the characteristics which they to. It is the highest aim of the biometrical study of variation do determine the biological causes which underlie the formation of the « particular » sort of frequency curves which actually are found, rather than some one of the innumerable other sorts which might conceivably have arisen in any individual instance! A « first study » in this direction
was made by the writer for variation in the plant Ceratophyllum[1] . More recently very fundamental researches of a
- ↑ Carnegie Institution of Washington, Publication no. 58, 1907.
