Question

NOVA BECOMING HUMAN

1) Why do researchers suspect that Sahelanthropus was more likely a human ancestor, and not an ape ancestor?

2) Until quite recently, aprominent hypothesisin the origin of humans was that bipedalism and increased brainsizeevolved simultaneously. What evidence is calling this hypothesis into question now?  

Answer 1

Initially, Sahelanthropus was considered as a human ancestor because they had a flat face, and the tip of the canine tooth was worn down similar to humans.

In 2006, the researchers examined the structure and function of the reconstructed skull of Sahelanthropus. The anatomical position of foramen magnum in Sahelanthropus is similar to humans, but the other structures does not allow its species to keep their head in upright position (so, not a bipedal walker). So, the scientists assumed that Sahelanthropus was a kind of ape, but not a hominid, or it might have shared some hominid features due to parallel evolution.