ID# 1854:
"The Complex Determinants of Amentia," by L.S. Penrose, Eugenics Review (vol. 26:2)
Date:
1934
Pages: (1|2|3|4|5|6)
Source:
Cold Spring Harbor, ERO, The Eugenics Review, 26

&quote;The Complex Determinants of Amentia,&quote; by L.S. Penrose, Eugenics Review (vol. 26:2)

124 The Eugenics Review therefore applies equally to that group of defectives which can be regarded as belonging to the normal distribution. I have previously pointed out that the major accidental occurrences which alter intelligence are more likely to reduce it than to raise it. Accidents may be either environmental or genetic and they may be in the nature of infectious diseases or injuries to the nervous system, or they may be the effects of uncommon gene mutations. Now these factors do not all produce their effects in the same way. There are two main ways in which they behave, and these two ways are logically distinct. In the first place, the effects may be cumulative. Thus, to take a simple example, a child who contracts encephalitis lethargica loses, on the average, about six points in its mental ratio (or intelligence quotient) in two years, and the deterioration is progressive. A child with an initial ratio of 110 is in little danger of becoming mentally defective under such circumstances. On the other hand, a child with an initial ratio of 80 may be expected, about three years after the onset of the disease, to reach a level of intelligence within the range of mental deficiency. Here the initial dullness, with the superadded disorganization of the brain, causes the borderline to be overstepped. Subcultural mentality plus organic disease is a potent cause of mental deficiency. In the second place, accidental factors may combine to produce inferior intelligence, though they have little or no effect on mentality when they act separately. The hereditary predisposition to a certain type of disease may be of no consequence if precipitating factors are absent from the environment. If susceptibility to tuberculosis were entirely hereditary, this would be of little consequence to susceptible individuals unless tubercle bacilli existed in the environment. Conversely, the presence of pathogenic organisms would be of no significance to an immune race. The coexistence of susceptibility and a precipitating factor, however, produces a disease. Not improbably, in some of the infectious diseases which appear to cause mental deficiency, the question of inherited diathesis is of importance. Possibly this is so in syphilitic amentia: some other types of encephalitis also seem to run in families. Examination of Specific Instances By examining exceptional types, we are able to identify most effectively the individual factors which can combine together in these complex ways to produce inferior mental ability. Mongolism is a type of mental defect which occurs in all classes of society: it may be due to the product of gene factors and specific prenatal environment. There is very little doubt that the maternal age at a child's birth is a potent cause. The father's age and the birth order seem to be of no significance. On the other hand, maternal age does not seem to be the only causal factor: incidence is higher among some races than among others and some families appear to be particularly prone to produce mongol children. Like twins have always been observed to be equally affected and mongolism is often found in one of a pair of unlike twins. These facts support the view that, while one child can have a predisposition to become a mongol if the mother is elderly, other children in the same sibship can be immune. But maternal age at the birth of a child is not itself a pathological circumstance. Nor are English people to be regarded as especially pathological on account of the relatively high incidence of mongolism in this country as compared with some others. The question of predisposition is also important when we notice how frequently the mentally defective suffer from some form or other of mental derangement. Experience in the field of mental diseases leads us to expect that some psychoses are the combined product of inherited predisposition and mental strain. The mentally disordered patient usually has an intelligence which is lower than would be expected if his faculties were well co-ordinated. There is a great deal of difference between the initial capacity of a patient who is a reliable, steady worker, and that of a patient of similar mental age who suffers from severe psychosis or epilepsy. [end]

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