Phylogenetics and Classification

Current thinking about phylogenetic relationships is expressed in branching diagrams of one kind or another.

Since opinions often differ about which diagram is best, alternatives co-exist for long periods until the weight of evidence forces some schemes to be abandoned.

Classification schemes are different. They provide a vital framework for taxonomic communication. Too much change would be confusing. Yet most biologists want classifications to reflect the real evolutionary picture, so even classifications undergo change - but more slowly than phylogenies.

Many techniques exist for constructing classifications, not all of them mutually compatible.

Phylogenetics and Classification of Hominoids

• How would you go about classifying the hominoids?
• What features would you depend on most?
• How would you classify a primate that looked and behaved like us but had been phylogenetically separate from us for longer than the chimpanzee?
• Alternatively, how would you classify a primate that didn't look or behave at all like us, looked much more like the chimpanzee but had separated from the hominid lineage much more recently than the chimpanzee?
• Would you give priority to the similarities between the species, and classify like species together?
• Or would you give most importance to the recency of their common ancestry - i.e. in the true branching pattern of evolutionary descent irrespective of similarity - and so classify close relatives together?
• Or would you try to take both similarity and common descent into account at the same time, by grouping like species together but arranging them in accordance with known relationships wherever possible?

You will find a useful discussion of these issues in Chapter 1.2 of [Jones et al. 1992] .