Truth in Science

Biology 2. Jones, M., and J. Gregory. 2001. Cambridge University Press, Cambridge.

Organisms can be classified according to their evolutionary relationships. In order to do this, taxonomists look for shared homologous features between living organisms. These are features which appear to have similar underlying designs, and so have almost certainly evolved from the same ‘original’ design that existed in a particular organism at one stage. A classic example of homologous features is the limb bones of vertebrates. In all birds and mammals, for example, these limb bones take the same general pattern with a single bone in the upper limb and two bones in the lower limb. You can always pick out this pattern, despite great variations in the way the pattern has been modified in the course of evolution. Such features supply strong evidence that all organisms possessing them had a common ancestor.