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The degree of intelligence inherited would seem to be very much the same for all classes. Once inherited, however, it is developed or retarded to a very large extent by environment. There seems, then, no good ground for the fear that the intelligence of the nation will sink to low level if the upper classes many. There is no evidence that society is so constituted that those of the lower classes have genes inferior to those of the upper.
There is, nevertheless, a type of low intelligence t be found in individuals spread fairly evenly through all ranks of society, namely, feeble mindedness. These people are apt to become a burden on the rest of the community, since many of them are kept in special institutions maintained by the rates.
Feeble mindedness is definitely inherited, although the exact mode of inheritance is unknown. It is certainly not due to the transmission of a single character, or gene. For instance, if both parents are feeble minded, about sixty percent of the children inherit this condition. If one parent only has this characteristic, about twenty nine percent of the children are feeble minded.
From these facts certain conclusions can definitely be drawn. If , like albinism, feeble mindedness were a single recessive, in the case of both parents having the character ,not sixty percent only, but all the children would be feeble minded. Feeble mindedness then is not a single recessive. Were one parent feeble minded and the other normal, and were this character a dominant fifty percent of the children would inherit the factor. But, infact, only twenty nine percent do so. Equally, then feeble mindedness is not a single dominant. Various indications suggest that there are two recessive genes which most combine in order to produce this condition.
As those of feeble mind tend to marry their own kind and to have more children than the average normal family, it is often advocated that such persons should be sterilized,such sterilization consisting of a slight operation upon the male partner of the marriage which renders him incapable of propagating but leaves him sexually capable in all other respects.
Yet the prevention of such people from reproducing will not considerably reduce the number of the feeble-minded, since gees for this condition are fairly wifely distributed in normal persons, and the bringing to light of this feeble mindedness is no more than an unfortunate gene combination in this or that particular mating.
Various forms of mental defect are inherited, and it has been proved that the mode of inheritance differs according to the form. An instance is amaurotic idiocy a form of idiocy which appears between the ages of six and fourteen, the sufferers from which die before they reach the twenties, because the fats are not properly assimilated by their bodies. This is due to a simple recessive gene, similar to albinism and inherited in the same way. Likewise you can come across several findings which makes more interesting and expedient facts.
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