The five Kingdom system is more specific, in a way, but the three domain system allows to go back further and recognize a common ancestor.

That is one of its greatest benefits: it shows how different kingdoms are related to each other. It also explains archaebacteria much better.

Thanks Dhamesh. The 3-domain system will imply 6 kingdoms, and Monera will be represented by Archae and Eubacteria, isn't it? Are there other reasons why 3-domain system has an advantage?

@Miranda: 3 domain system differentiates better not only in the case of eubacteria and archae but also significantly subdivides protista. Also the 3 domain system is based on differences between rRNA gene as given by Woese et al. Please go through the paper provided in the link http://www.pnas.org/content/87/12/4576.full.pdf.

Thanks. We have been teaching Whittaker's 5-kingdom for many years. Now I see the need to change!

@Miranda: If I may suggest, do not remove 5 kingdom system from the course and add 3 domain system to it. It will give a better understanding of the subject to the students.

Yeah, there is a lot more.

The pdf link given by Mr. Prashant contains lot of information. It should help you.

And yeah, you should not make it complex.

As a student i would suggest start from the easy part (basics) and then move on to complex.

Thanks, I can see the point. Students should actually know the progress of this 'history' of classification of organisms :)

I have difficulty with artificial levels of phylogeny like 'kingdom'. Beginning students should be introduced to the theories represented in phylogenetic charts or cladograms, and should be led to understand the arbitrariness inherent in the creation of names to represent defined clades. Scientific inquiry into pathways of evolution should receive emphasis over the memorization of names assigned to clades that have been identified. Students should also be educated in theories related to movement of genes between unrelated organisms. The 'history' of classification is simple: for a long time groups were based on similarity, and evolution was not known, and now it is generally accepted that groups should represent clades. At the same time, some people still accept the notion that a group (e.g., Osteichthyes) can still represent a 'level of evolution', not a clade. This dispute has not yet been resolved, but most cladists think that it has been resolved. In any case, this is a question of definitions that has no impact, and is not impacted by, scientific inquiry. Students should at least know the difference between a clade (e.g. Eucrustacea) and a group of related organisms that is not a clade (e.g. Crustacea).

@David: I do not agree with you. I think first even you learned about the existing classification and over a period of time developed your opinions. In the same way students should also be told not only about the current system of classification but also what system were used previously. It is only in this way a student can really appreciate the progress of science and it would be easier for him to understand the actual significance of classification.

One needs to know older, discarded taxa only to interpret old literature. In concept classification from the time of Linnaeus to the present day is not a difficult subject to master. The question of the scope of a taxonomic unit cannot be resolved by either ICZN rules or by scientific inquiry as it is arbitrary and any schema of classification cannot be falsified, hence this is not science. However the hypothesis of whether or not a taxon is monophyletic or polyphyletic is subject to scientific testing or falsification. For science, phylogeny is relevant.