Answer:
Due to overlapping classifications and inability to classify organisms with limited information
Step-by-step explanation:
Earlier the classification systems were based on the similarities and dissimilarities between the morphological traits of organisms. However, with discovery of more and more species it was found that several organisms with in the same species have different characteristics while organisms from different species have similar characteristics. In order to study all these variations , genetic engineering was used. This lead to a newer classification system where species are now defined based on their genetic structure and evolutionary history.
This new approach of classification also led to creation of new sub species group within the same species.