The father-mother family with two children isolated in a city flat is already insufficient.

I owe undying gratitude to my patient parents.

Ethologists are often accused of drawing false analogies between animal and human behaviour. However, no such thing as a false analogy exists: an analogy can be more or less detailed and, hence, more or less informative.

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.

When I was about ten, I discovered evolution by reading a book by Wilhelm Boelsche and seeing a picture of Archaeopteryx.

I consider early childhood events as most essential to a man's scientific and philosophical development.

There is indeed the possibility that the evolutionary process has, in gray antiquity, bred into us an excess of aggression.

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.

I grew up in the large house and the larger garden of my parents in Altenberg. They were supremely tolerant of my inordinate love for animals.

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.