Derek Butler

People do usually say that nature is our mother. It gives a person everything that is necessary for life, even though we don't always appreciate its gifts. What could be better than the warm sun, majestic mountains, and blooming trees in the spring? The world of nature is very rich and varied. There are hundreds of thousands of species, many of which we've never seen in our life.

Except perhaps for the possession of collagen, the criteria used above to distinguish animals from other forms of life are not absolute. The first catalogs of animal diversity were based on overall form and similarity. Aristotle and other early biologists regarded all organisms as part of a great chain, divisions of which were more or less arbitrary.