(a) The earlier botanists and zoologists who wanted to study plants and animals faced great difficulty in their systematic study. Because it is not possible for a person to know and remember about every plant or an animal individually. Moreover, different species of plants and animals were known by different names in different parts of the world.
(b) These two things created great difficulties. In order to overcome these difficulties all the earlier biologists tried to classify them into various groups, though in the beginning the attempts to classify them were not on scientific lines. But all were same without classification and proper study of organisms were not possible. To overcome this all the earlier biologists try to classify living things in order to study them.
(c) It is on this account that all the earlier biologists were mostly taxonomists.