Question

When scientists questioned the traditional classification of Kingdom Animalia, what evidence was used to indicate that the traditional classification was inaccurate? Discuss the changes that occurred under the new classification scheme. What has remained the same?

Answer 1

Tale of Traditional Classification:

Robert Whittaker's five-kingdom system was once used as the main model for animal classification which served as an important organizing scheme for discussing biodiversity. Followed was the famous and most widely accepted Linnaeus classification which revolutionized the field of biology by introduction of a method of naming the species called taxonomic nomenclature. He divided the biodiversity into 3 kingdoms and in that he used five ranks: class, order, genus, species, and variety.

During the time other ranks have been added to the taxonomic nomenclature system. The primary taxonomic ranks used are

1.) Kingdom

2.) Phylum

3.) Class

4.) Order

5.) Family

6.) Genus

7.) Species

This method was used to define and understand animal classification for a long time. From childhood we used to refer birds to “Class Aves,” Fish to “Class Pisces,” which is also a Zodiac sign. But the evidence that was used to account for inaccuracies was that the Physical similarities between two species are not always a result of the species being closely related. Linnaeus' system does not account for similarities that are evolved this way or molecular evolution was not considered. The main thing to focus on this limitation was that there was no potential instrument or analysis method to analyse such inaccuracies.

Major Changes:

Main Driving factors for the change is the more advanced and improved technologies that are constantly changing our dynamic world. The invention of microscope has enabled the biologist to see what they hadn’t been able to see before. All in all, this allowed the researchers to re-assess the relationships between organism which ultimately refined the fine-tuned the classification system.

Modern Classification:

Modern classification considers the physical traits which were used in earlier classification but puts greater emphasis on evolutionary history. A tree like structure called cladogram is used to show these differences by nodes and branches. Molecular classifications are determined by comparing similarities and differences in living things that share common ancestor. A phylogenetic tree aka cladogram could be used to show how birds share a common ancestry with snakes and crocodiles.

Evolutionary relationship has dramatically changed the way we used to classify earlier. Let’s for example, Chimp shares 99.5% gene conservation with humans and mouse shares 88% on the other hand. Let’s talk about the differences between the two which will provide more clarity on the inaccuracies as well as adopted changes in the new system.

Traditional classification mainly followed the structural similarity. For example, all animals having a particular characteristic such as tail evolved from same recent common ancestor. But the main problem with this theory was the convergent evolution concept. In this type of evolution, the organisms that are not closely related to each other develop the same trait over some period of time. This can happen when two distantly related organisms have to adapt to let say environmental pressure. The Molecular aka Evolutionary classification can resolve this problem. It is based upon the molecular makeup of the organism rather than specific structural trait. It says that the change in the appearance or in the behaviour is due to the genetic code which is the building block of DNA. But observable changes or appearance is not solely because of the mutations in the genetic code. Thus, molecular phylogenetics can only detect relationships that are not reflected in observable characteristics.

With introduction of evolutionary relationship more controversies have erupted and the relationships have become more confusing as earlier the animal groups were defined using ranks. Although many scientists agree that ranks are no longer a useful aspect in animal taxonomy. However, ranks remain widely accepted and recognized form of method in Biological history, though their usage is limited and might disappear in the future. Still people use ranks as the form of teaching the contradiction. Also, as a zoologist you should understand this as the unfortunate output of merging two widely used but incompatible systems of classification.