Page:Popular Science Monthly Volume 80.djvu/91

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87
MENTAL DEFECTIVENESS

THE ORIGIN AND CONTROL OF MENTAL DEFECTIVENESS
By Dr. CHAS. B. DAVENPORT

STATION FOR EXPERIMENTAL EVOLUTION, CARNEGIE INSTITUTION OF WASHINGTON.

NOT long ago I spoke to a company of physicians and lawyers on inheritance of certain types of imbecility, and exhibited some charts that showed that imbecility in a child is due to defects in the germ-plasm of both his parents. At the end of my remarks the chairman pointed out that the facts presented merely deferred the origin of feeble-mindedness a generation or two and did not touch on its true cause. I find this idea wide-spread; the point raised consequently deserves further consideration: How did feeble-mindedness originate in the first instance?

Before we can answer the question as to the "cause" of feeble-mindedness it is desirable to get a clear definition of the term. As a matter of fact, very diverse definitions have been offered. An old legal formula is as follows: "He that shall be said to be a sot and idiot from his birth is such a person who can not count or number twenty pence, not tell who was his father or mother, nor how old he is, so it may appear that he hath no understanding or reason what shall be for his profit or what for his loss; but, if he have sufficient understanding to know and understand his letters, and to read by teaching or information, then it seems he is not an idiot." While this definition lacks in completeness and scope, it has a more philosophical basis than many that are more recent. Of late the Binet-Simon tests of mental grade have aroused new enthusiasm and have been thought to give an exact, quantitative measurement and definition of the different classes of mental backwardness. The method is simply that of establishing a series of mental standards (questions, exercises, mental feats and so on) for each year of school life, grading a given subject by these standards and finding the difference between the actual age of the subject and the standard age of the highest test passed by him. This method of defining feeble-mindedness seems to assume that there is a greater mental resemblance between two persons deficient three years than there is between one who is deficient three years and one who is deficient four years. And that, it seems to me, is fundamentally erroneous. For the modern biologist is coming to rely less on the idea of races or groups and to realize that, in nature, we have only individuals, made up of collections of traits that are, for the most part, separately inheritable. Not individuals, but their transmittable characters, are