Scientists argue ape-like Sahelanthropus tchadensis that lived in Africa 7m years ago is best contender but more fossils are needed

In the murky first chapters of the human story is an unknown ancestor that made the profound transition from walking on all fours to standing up tall, an act that came to define us.

The odds of stumbling on the fossilised evidence of such an evolutionary prize are slim, but in new research, scientists argue that an ape-like animal that lived in Africa 7m years ago is the best contender yet.