The Comparative Approach in Biology
Model organisms in biology—also known as model systems—provide important ways to study biological phenomena under controlled laboratory circumstances.

A richer perspective is found when studying the diverse and remarkable ways that plants, animals and other living systems have adapted to their particular ways of life in their natural settings. A great deal can be learned by comparing the various ways that specific organisms have adapted. This general approach is known as Comparative Biology.

Sex Determination, Biochemical and Physiological Adaptation
Comparative Biology shows that sex determination is quite variable in nature. In bony fishes, depending on the species, determination of which individuals will develop as females and which will develop as males may depend not only on the chromosomes, but also on environmental conditions such as temperature or water conditions. Sex determination is a good example of biochemical and physiological adaptation—evolutionary changes that make it possible for various species to survive under unique, and sometimes harsh, environmental conditions.