matings, and in such a way that, on the average, similar individuals tend to marry.
These results will probably be received with much scepticism. The "charm of disparity," the "selection of opposites," has been so long asserted that the notion will not readily be given up. Concretions of vague impressions compacted into popular superstition are not soon broken up by the hammer of logical deduction from scientific measurement. This scepticism of preconception can, however, be ignored; in time it must give way to orderly arranged facts. Yet the scientist should not forget that when cracked open, the nodules of popular belief are often found to contain a scrap of truth—and in his turn should avoid dogmatism.
Purely biological phenomena are far more complex than the majority of naturalists have realized. When social factors are superimposed the difficulties of research become almost unsurmountable. Pearson has warned us that "in many factors there may actually be two opposed currents, one giving a tendency for like to mate with like and the other marked by the fascination of extremes." Goring's studies of criminals vindicate one's a priori conviction that assortative mating may be influenced by social conditions. Human society differs so profoundly from place to place and time to time that, however great the temptation to generalization may be, it would be folly to press the conclusions far beyond the data which they represent.
Moreover, if the biometric results reviewed in the preceding pages must be fitted post haste into some evolutionary scheme, or find an immediate practical social application, each reader must be responsible for his own. The difficulties of interpretation are even greater than the dangers of generalization. To-day, an unfortunately insistent demand that every datum must count for or against some current theory has largely replaced the Darwinian spirit of collecting facts in the hope that when sound and sufficiently numerous, reasonable theories may be fitted to them. To-day "a fact is not a fact until it fits a theory." Personally, I feel as thoroughly satisfied that the time is not yet ripe for interpretation as I am completely convinced that in the differentiation and painstaking measurement of the intensity of the individual possible factors we have begun to move in the right direction in the attack upon the phalanx of problems which we designate as organic evolution. The immense value of these pioneer studies by Pearson and his associates lies in the fact that they represent the definite and substantial beginning of quantitative research which is so large a part of the solution of a problem.