When Aristotle classified the living world into animals and plants, he grouped fungi with plants because of their lack of motility. As discussed in Chapter 27, molecular sequence comparisons now make it clear that fungi are actually related more closely to animals. In fact, it would not be amiss to refer to mushrooms and molds as our “cousins.”

Fungi share a number of features with animals: Their motile cells, when present, have a single flagellum attached to their posterior ends; fungi and many animals synthesize chitin; and fungi store energy as glycogen, as do animals. Nevertheless, the last common ancestor of fungi and animals was a single-celled microorganism that lived in aquatic environments about 1 billion years ago. Multicellularity evolved independently in fungi and animals (Chapter 28), and so the fungi have many features that are unique in the biological world.