Charles Darwin put forward the idea of evolution in 1859, in his book, The Origin of Species. Ernst Haeckel, Robert Whittaker and Carl Woese have tried to classify living organisms into broad categories, called kingdoms. Robert Whittaker, in 1969 proposed ‘Five kingdoms classification’ of living organisms.
The hierarchy can be represented as Kingdom sub grouping into Phylum for animals or Division for plants, Class, Order, Family, Genus and Species. Hence, the basic unit of classification is species. Species includes all the organisms that are similar to breed and produce fertile offspring.
