Social environment and moral progress / by Alfred Russel Wallace.

  • Alfred Russel Wallace
Date:
1913
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Social environment and moral progress / by Alfred Russel Wallace. Source: Wellcome Collection.

    91/180 page 79
    Х1П] Selection in the Animal World before but slightly exercised, and then greater development follows as a consequence of their more frequent use. Other organs, no longer in use, are impoverished and diminished in size ; nay, are sometimes entirely annihilated, while in their place new parts are insensibly produced for the discharge of new functions. Again, he says : Thus otters, beavers, water-fowl, turtles, and frogs were not made web-footed in order that they might swim ; but their wants having attracted them to the water in search of prey, they stretched out the toes of their feet to strike the water and move rapidly along its surface. By the repeated stretching of their toes the skin which united them at the base acquired a habit of extension, until, in the course of time, the broad membranes which now connect their extremities were formed. In the case of plants, where no volun¬ tary movements occur, the cause of modifi¬ cation was said to be due almost exclusively to the change of local conditions, as the various kinds of plants became dispersed over the earth's surface. The influence of soil, of temperature, of light and shade, are supposed to produce definite changes which are gradually increased ; just as plants long cultivated in our gardens have become so changed that the wild progenitors cannot now be recognised. 79
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