Nested Hierarchies

Common ancestry is conspicuous.
Evolution predicts that living things will be related to one another in what scientists refer to as nested hierarchies—rather like nested boxes. Groups of related organisms share suites of similar characteristics and the number of shared traits increases with relatedness. This is indeed what we observe in the living world and in the fossil record and these relationships can be illustrated as shown below.

In this phylogeny, snakes and lizards share a large number of traits as they are more closely related to one another than to the other animals represented. The same can be said of crocodiles and birds, whales and camels, and humans and chimpanzees. However, at a more inclusive level, snakes, lizards, birds, crocodiles, whales, camels, chimpanzees and humans all share some common traits.

Humans and chimpanzees are united by many shared inherited traits (such as 98.7% of their DNA). But at a more inclusive level of life’s hierarchy, we share a smaller set of inherited traits in common with all primates. More inclusive still, we share traits in common with other mammals, other vertebrates, other animals. At the most inclusive level, we sit alongside sponges, petunias, diatoms and bacteria in a very large “box” entitled: living organisms.

	Lesson plans for teaching about phylogeny