Classification and Evolution

All living things are identified and categorised on the basis of their body design in form and function. Some characteristics are likely to make more wide-ranging changes in body design than others. There is a role of time in this as well. So, once a certain body design comes into existence, it will shape the effects of all other subsequent design changes, simply because it already exists. In other words, characteristics that came into existence earlier are likely to be more basic than characteristics that have come into existence later.

Most life forms that we see today have arisen by an accumulation of changes in body design that allow the organism processing them to survive better. Charles Darwin first described this idea of evolution in 1859 in his book, The Origin of Species.

When we connect this idea of evolution to classification, we will find some groups of organisms which have ancient body design that have not changed very much. We will also find other groups of organisms that have acquired their particular body designs relatively recently. Those in the first group are frequently refferred to as ‘primitive’ or ‘lower’ organisms, while those in the second group are called ‘advanced’ or ‘higher’ organisms. In other words, it can be said that first formed (ancient, older) organisms are simpler, while younger organisms (later formed, modern) are more complex, i.e., complexity in design of simpler forms has increased over evolutionary time, so that they ultimately become more complex.