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Mendel's theory like Weismann's has the idea of germinal continuity for one of its foundations. It conceives of the hereditary relation as one between the parental and filial germ cells and not between the bodies of parent

[graphic][subsumed][subsumed][subsumed]

FIGURE 6. Mendelian Inheritance in Four-o'clocks.

and offspring. Mendelism explains the organism as built up of a number of definite and separably inheritable characters. Variation seems to consist in the presence or omission of elementary factors. Thus, the white sweet pea was brought about in the variation by which one of the color factors was dropped out. Variation is not always the progression from a lower degree of com

plexity to a higher, but the reverse may be true.1 Thus experimental breeding has shown that the white coat of the horse is not a simple character, but is due to several independently inheritable factors.15

Besides the Mendelian theory of inheritance there is one other theory: Francis Galton's theory of Regression. The theory as first expounded was based upon the measurements of the stature of over 900 English individuals.16 Galton found that the form of the body of an individual is determined by the racial type to which the parents belong, modified, however, by a tendency of reversion to a type intermediate between the special variations presented by the parents. For example, if the father of an individual is exceedingly tall, and his mother somewhat taller than the average, it is often found that the children tend to develop a stature which is somewhat near the general type, but at the same time dependent upon the intermediate value located between the stature of the mother and that of the father. In accordance with this theory it was found that the influence upon the individual of inheritance was about 14 from each parent and c from each grandparent. This law of regression was found to hold for the inheritance of stature, eye-color, and artistic ability. More recent studies have shown that the intensity of heredity for each parent may be expressed by about one-third.17 The principle of regression may be made clearer by quoting from Professor Boas: "Provided the mother differs in her stature by an amount of 9 cm. from the racial norm,-for instance, if

14 Thomson & Geddes, op. cit., p. 137.

15 Davenport, op. cit., p. 24.

16 Galton, op. cit., chs. vi. and vii.

17 Pearson, K.-"On the Laws of Heredity in Man," Biometrika, vol. ii, p. 357 et seq.; and Boas, F.-"Heredity in Anthropometric Traits," Amer. Anthropologist, N. S., vol. ix, p. 453 et seq.

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she is 9 cm. taller than the average individual, then we may expect the child to be one-third of 9 cm., or 3 cm., above the average. It will thus be seen that if both parents differ in the same direction from the average, the effect of both will be cumulative; and if both differ from the average of their people by the same amount, the joint effect of the two parents may be expressed by the coefficient of about two-thirds. In case, for instance, both father and mother should be 9 cm. above the type average, we should expect the child to be about two-thirds of 9 cm., or 6 cm., above the average.

9 18

These variations, inherited in accordance - '

(

that have been outlined, form what has called the "raw materials" origin of these variations we know cosm of the germ cells there goes c ordinarily intricate permutation Weismann supposes that there is germ cell between rival hereditary may be, there is much research still can hope to speak in dogmatic fasl variations.

SUPPLEMENTARY REA

BOAS, F.-The Mind of Primitive Man.
CRAMPTON, H. E.-The Doctrine of Er
DARWIN, C.-The Origin of the Species

DAVENPORT, C. B.-Heredity in Relation to Eugenics.

GALTON, F.-Natural Inheritance.

KELLICOTT, W. E.-The Social Direction of Human Evolution. METCALF, M M.-Organic Evolution.

PUNNETT, R. C.-Mendelism.

ROMANES, G. J.-Darwin and After Darwin, I The Darwinian

Theory.

18 Boas, op. cit., p. 82.

THOMSON, J. A. & GEDDES, P.-Evolution (Home University

Library).

THORNDIKE, E. L.-Individuality.

WEISMANN, A.-The Evolution Theory.

II

THE STRUGGLE FOR EXISTENCE

HAVE you ever strolled across the sunlit meadows and then entered the cool silence of the forest and wondered at the apparent contentment and peace that reigned everywhere? The flowers were all so bright and birds chirping or singing in the trees seemed to lead lives of quiet uneventfulness. But look closer, and back of the silence of the forest is the cringing fear of every living thing. Under the apparent calm of nature there is the constant and bitter struggle for food, air, and space,for life. All the trees and flowers, all the birds and other animals are engaged in a continual struggle for existence. There is struggle between plants and animals of the same species for the same food and space; the struggle of each and all against unfavorable conditions of climate, heat and cold, flood and drouth; the rivalry between them for mates; and a continual effort to rear their young in the face of that stern necessity which decrees that in spite of the strenuous efforts put forth, in a great majority of cases there is only failure and death.

This fearful struggle for existence is the consequence of two facts: first, the amount of food and space upon the earth for plant and animal use are limited; and, second, the process of reproduction, if unhindered by any adverse circumstances, tends to increase the number of individuals in any given species in geometrical ratio. This means that in every generation of every species a great

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