In the course of evolution, it constantly happens that, independently of each other, two different forms of life take similar, parallel paths in adapting themselves to the same external circumstances.

Whenever we find, in two forms of life that are unrelated to each other, a similarity of form or of behaviour patterns which relates to more than a few minor details, we assume it to be caused by parallel adaptation to the same life-preserving function.

Practically all animals which move fast in a homogeneous medium have found means of giving their body a streamlined shape, thereby reducing friction to a minimum.

Konrad Lorenz Quotes