5 - Constructing Phylogenetic Trees

Summary

Having modeled the evolution of DNA in the last chapter, we are now ready to use these models to make important deductions from real DNA data. We will see how a model of molecular evolution, together with some new mathematical techniques, can be used to deduce evolutionary history.

Let's consider a well-studied, yet still compelling question: What is the relationship of humans to the modern apes? More specifically, which of the gorilla, chimpanzee, orangutan, and gibbon are our closest evolutionary kin, or are all these apes more closely related to each other than they are to us?

Early evolutionists viewed the chimpanzee and gorilla as our closest relatives. Humans and these African apes were believed to form one evolutionary grouping, which had split from other ape lineages in the more distant past. A bit later, the dominant view became that all the modern apes were more closely related to one another than to humans. Two possible diagrams that represent more detailed versions of these competing views of hominoid evolution are shown in Figure 5.1.

▶ Since the chimpanzee and gorilla are African, whereas the orangutan and gibbon are Asian, what, if anything, would each of these trees indicate about the likely location of the appearance of the first humans?

How can we choose which of these or the many other possible evolutionary trees is the best description of hominoid descent?