Mushrooms are closer cousins to animals than to plants
Sorting living things by looks once seemed obvious. Then biologists began grouping organisms strictly by ancestry, into clades made of one ancestor plus every one of its descendants, and the family tree rearranged itself. Fungi turned out to be nearer relatives of animals than of plants, and archaea split away from bacteria.
The word clade comes from the Greek for branch. Julian Huxley coined it in 1957, borrowing the underlying idea of one species splitting into two from Bernhard Rensch. His grandfather Thomas Henry Huxley, an early champion of Darwin, had proposed a classification resembling clades back in 1876. The German biologist Willi Hennig is usually credited as the founder of cladistics, the method built on clades, while Ernst Mayr supplied the term itself in 1965.
Hennig's big change was replacing a ladder with a tree. Older schemes arranged life in a line from supposedly primitive to supposedly advanced forms, and Linnaeus had grouped organisms purely by physical resemblance, which convergent evolution can badly mislead. A clade instead includes an ancestor, known or unknown, and all its descendants, living or extinct, and clades nest inside one another like branches on branches. Apes are a clade within primates; lemurs and lorises are sister clades sharing an immediate ancestor.
Timing is harder to pin down, because no one can watch a branch form. Biologists distinguish a clade's crown age, the date of the latest common ancestor of its living members, from its stem age, when its lineage split from its sister group. Both are estimated from fossil layers or molecular clocks. Naming is contested too, since traditional ranks run out long before the nesting does: the mallard duck can be placed in more than 40 successive clades.
The idea reaches beyond animals and plants. RNA viruses form clades that help epidemiologists follow outbreaks; HIV subtype B dominates in Europe, the Americas and Japan, while subtype A is more common in east Africa. Even the naming conventions have quirks, such as the reptile clade Dracohors, 'the dragon cohort', a rare exception to the rule that clade names are plural.
Source: Clade
