AS OUR understanding of evolution evolves, so do the terms we use to describe the relationships between species. 鈥淗ominin鈥� is intended to clarify the links between humans and their nearest relatives. Instead it has caused immense confusion. Here鈥檚 the first tip: hominin is not a typo for the older and more familiar term 鈥渉ominid鈥�.
This year is the 300th birthday of Carl Linnaeus, the father of modern taxonomy and the person who, unwittingly, is to blame for the confusion. According to his classification system, all living things should be identifiable by a simple chain of 鈥渢axons鈥�: kingdom, phylum, class, order, family, genus and species. The evolutionary relationships between taxons dictate what fits where. Two species with the same most recent ancestor, for example, should be in the same genus. A similar pattern extends back up the chain.
Humans are easy to classify up to a point: animal, chordate, mammal, primate鈥� but then things get tricky. Biologists used to put modern humans and our closest extinct ancestors in the family Hominidae 鈥� our old friends the hominids 鈥� and other apes in a separate family, Pongidae. We have since learned that this last family makes no evolutionary sense.
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Different apes split from the line that leads to humans at different times. The first to go were the orang-utans, which left a line leading to the African apes: gorillas, chimps and humans. So the meaning of the word 鈥渉ominid鈥� was changed to include just these three.
To cope with this change, taxonomists levered in a new taxon 鈥� subfamily. About 10 million years ago the gorillas peeled off to form the subfamily Gorillinae. Three million years later the chimps formed the subfamily called Panini. What was left became the subfamily Homininae, or hominins: modern humans plus every creature closer to us than chimps.
It鈥檚 OK to be confused: you鈥檙e only a hominin after all. But let鈥檚 make things even worse. Go up one level from the hominid family and you find a 鈥渟uperfamily鈥�, called Hominoidea or hominoids, which includes the gibbons and orang-utans. This taxonomy might be less taxing if all the names did not start with the same two syllables. As new finds are made, it鈥檚 only a matter of time before we reach hominaaargh!
鈥淚t鈥檚 only a matter of time before we reach hominaaargh!鈥�
Search the web and you鈥檒l find several conflicting versions of this explanation. Our description comes from Simon Underdown of Oxford Brookes University, UK, who recently tried to clarify the matter in Nature (vol 444, p 680). So, here is some sage advice. First, hominin means today what hominid meant 20 years ago. Second, an offering from Harvard anthropologist Daniel Lieberman: 鈥淚 prefer to use 鈥榟ominid鈥� as a colloquial, but use 鈥榟ominin鈥� when I am being cladistically formal.鈥� Let鈥檚 face it, there鈥檚 no hope.
