Page:Popular Science Monthly Volume 80.djvu/480

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HE supreme misfortune is when theory outstrips performance." wrote Leonardo da Vinci.

He gave us, as far as I remember, no illustration of his epigram, but one is at hand in the modern attitude towards the Darwinian principles of natural and sexual selection. Exalted as they were on comparative evidence alone, and by post-Darwinian enthusiasts who were not only fertile, but liberal to a fault, in assumption, their debasement was inevitable. We are now in the period of reaction when men disparage selection, or dismiss it entirely as an evolutionary factor. Against this unreasonable extreme of opinion these essays are directed. They are simple reviews, pretending merely to set forth honestly the results secured by biometricians in their studies of these exceedingly difficult biological problems.

Their purpose is, I admit, in reality two-fold. Not only are they a direct plea for a more open-minded—a stringently critical rather than a dogmatic—attitude towards the Darwinian factors, but an indirect appeal for a wider recognition of the biometric methods which make possible the measurement of the intensity of the primary factors of organic evolution.

The strongest arguments are those of quantitatively expressed facts. The best way of overcoming the prejudices and other obstacles against which the biometrician works is to allow these facts to speak for themselves, if possible in terms comprehensible to the layman.

Let us turn, therefore, to the available facts.

There may be forces other than propinquity tending to fuse different races which through migration or otherwise come to occupy the same territory. Sociologists have, however, long emphasized intragroup marriages as one of the forces which tend to keep them distinct.