- The specimen must show differences from chimps and gorillas
- The specimen must resemble later hominins
- The specimen must be bipedal
The first two are just based on the principles of evolution, that for a species to be a hominin it must be different enough from its ancestors (which is assumed to be some sort of proto-chimp) that it belongs in a different subtribe than those that went before it. It also must resemble the later hominins in some way because it has to show that those hominins decended from these earlier ones. Lastly, of course, a specimen must be a habitual biped. This is the defining characteristic of hominins, and is what sets us apart from the other primates and mammals.
It is these three characteristics that I will be measuring the early possible hominins against. Over the next few weeks I will be looking at Sahelanthropus tchadensis, Orrorin tugenensis, Kenyanthropus platyops, and Ardipithecus ramidus and kadabba, and presenting evidence for and against their inclusion into the hominina subtribe.