Evolution Social and Organic

by Arthur M. Lewis

(1.) Every change in the environment of animals creates for them new needs.

(2.) These new needs will compel these animals to adopt new habits and discard some old ones, and these needs and habits will produce and develop new organs.

(3.) The development or disappearance of organs depends on their use or disuse.

(4.) The effects of use or disuse, acquired by animals, are transmitted by heredity to their offspring.

This fourth factor has split the biological world since Weismann repudiated it in 1883.

As a typical case of the operation of his theory, Lamarck gives the following: “The serpents having taken up the habit of gliding along the ground, and of concealing themselves in the grass, their body, owing to continually repeated efforts to elongate itself so as to pass through narrow spaces, has acquired a considerable length disproportionate to its size. Moreover limbs would have been very useless to these animals, and consequently would not have been employed because long legs would have interfered with their need of gliding, and very short legs, not being more than four in number, would have been incapable of moving their body. Hence the lack of use of these parts having been constant in the races of these animals, has caused the total disappearance of these same parts, although really included in the plan of organization of animals of their class.”

The idea of the serpent getting its long body, or the giraffe its long neck, or shore birds their long legs by “stretching,” has brought a good deal of ridicule upon Lamarck’s theory, and that part of it has never been taken very seriously.

This mistake however, will no more affect Lamarck’s title to a place among the immortals, than will the equally unfortunate theory of “pangenesis” endanger the status of his still greater successor—Darwin.

Lamarck’s glory is that he boldly proclaimed and largely proved the general theory of descent—biological evolution.

We shall now proceed to a consideration of the efforts of the great savants who have succeeded him, to ascertain its processes.