This article is reproduced with the permission of New Scientist for exclusive use by Nova users.

The word: Hominin
17 February 2007
From New Scientist Print Edition.

As our understanding of evolution evolves, so do the terms we use to describe the relationships between species. "Hominin" is intended to clarify the links between humans and their nearest relatives. Instead it has caused immense confusion. Here's the first tip: hominin is not a typo for the older and more familiar term "hominid".

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 "taxons": 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... but then things get tricky. Biologists used to put modern humans and our closest extinct ancestors in the family Hominidae - our old friends the hominids - and other apes in a separate family, Pongidae. We have since learned that this last family makes no evolutionary sense.

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 "hominid" was changed to include just these three.

To cope with this change, taxonomists levered in a new taxon - 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's OK to be confused: you're only a hominin after all. But let's make things even worse. Go up one level from the hominid family and you find a "superfamily", 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's only a matter of time before we reach hominaaargh!

Search the web and you'll 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: "I prefer to use 'hominid' as a colloquial, but use 'hominin' when I am being cladistically formal." Let's face it, there's no hope.

From issue 2591 of New Scientist magazine, 17 February 2007, page 52

For the latest from New Scientiist visit www.newscientist.com