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.
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.
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.
Every man gets a narrower and narrower field of knowledge in which he must be an expert in order to compete with other people. The specialist knows more and more about less and less and finally knows everything about nothing.
From a neighbour, I got a one-day-old duckling and found, to my intense joy, that it transferred its following response to my person. At the same time, my interest became irreversibly fixated on water fowl, and I became an expert on their behaviour even as a child.