Evolution and adaptation / by Thomas Hunt Morgan.

  • Thomas Hunt Morgan
Date:
1903
Catalogue details

Licence: Public Domain Mark

Credit: Evolution and adaptation / by Thomas Hunt Morgan. Source: Wellcome Collection.

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    the animal; but if it is true that the same change takes place in some of the lizards that live in the tropics, where the prevailing color is always green, it would appear that the result may have no direct relation with the surroundings. It has been shown in a number of well-authenticated cases that the pupae of certain butterflies vary in color within certain limits in response to the color of the background. When the caterpillar fixes itself to some surface, and there throws off the outer skin, and acquires a new one, the color of the latter is influenced by the background. The result is a better protection to the pupa. The change is not brought about through the ocelli or eyes, but through the general sur¬ face of the skin, for the same change takes place when the eyes have been previously covered with a dark pigment. The growth of plants toward the light may be looked upon as an adaptive process, since only in the light can they find the conditions necessary for their life. The extraor¬ dinary elongation of shoots and young plants when grown in the dark may also be considered an adaptation for finding the light, since in this way a plant, deeply embedded in the ground, may ultimately reach the surface. Thus while the actual process of elongation in the dark is not in itself of any use, yet under the ordinary conditions of its life, this response may be of great benefit to the plant. The closing together of the leaves of some plants has been supposed to protect them from too rapid radiation of heat, and incidentally this purpose may be fulfilled; but since some tropical plants also close their leaves during the night, it can hardly be maintained that the closing has been acquired for this purpose. It has been suggested that the opening of certain flowers under certain conditions of light is connected with the visits of insects that bring about cross¬ fertilization. The preceding examples will suffice to give a general idea of what is meant by adaptation in organisms. That
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