Mushrooms and other fungi are more closely related to humans and animals than they are to plants.

In 1969, scientist Robert Whittaker first suggested that fungi should be in their own group separate from plants. Genetic testing in the 1990s proved he was right. Scientists found that fungi and animals belong to a group called Opisthokonta.Fungi and animals share several physical traits. Both use a tough material called chitin for strength. Fungi use it in their cell walls, while insects use it to build their hard outer shells. Plants do not use chitin at all.Both groups also store energy using a sugar called glycogen. Plants store their energy as starch instead. Fungi even produce a molecule called ergosterol, which is very similar to the cholesterol found in humans.There are millions of different fungi species, but we have only named about 150,000 of them. Because our cells are so similar to fungal cells, it is often hard for doctors to create medicine for fungal infections. A drug that kills a fungus might also accidentally hurt human cells because they work in similar ways.