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Prehistoric World

Scientists Clash Over Skull

BBC News, 9 October 2002. Updated 19 April 2017

The war of words over the significance of an ancient skull known as Toumaļ resurfaced early in October 2002.

The fossil specimen was described as possibly the most important find of its kind in living memory when it was first presented to the media in July 2002. French palaeontologist Michel Brunet, who unearthed Toumaļ in Chad, said that it represented the earliest known hominid, or pre-human ancestor, yet found - it is almost seven million years old.

But some researchers voiced scepticism at the time and they soon went into print with their criticism. Brigette Senut, Milford Wolpoff, Martin Pickford, and others argued in the journal Nature that the skull was not on the human branch of the evolutionary tree at all.

Instead, they were saying, the specimen (formally classified as Sahelanthropus tchadensis) was probably that of an early gorilla or a chimpanzee, or a species that had since become extinct.

Walking upright

They put very different interpretations on the skull's features to that of Brunet. Its short face and small canines were female characteristics and were not conclusive evidence that Sahelanthropus tchadensis was a hominid, they believed.

Milford Wolpoff, a University of Michigan anthropologist, was adamant that Toumaļ was not human. His team focussed in particular on the 'scarring' on the skull left by neck muscles which could indicate how the spine related to the head, providing clues as to whether the creature could have walked upright.

In looking at the scars, according to Milford, they stated quite clearly that this animal did not habitually walk erect. It did not have human posture, and therefore it was not human.

Michel Brunet, of the University of Poitiers, hit back at the criticism, and was clearly irritated by the comments of his detractors. He accused them of being 'flippant', saying their statements were a 'curious' attempt to 'undermine... (and) misrepresent' his findings.

Peer review

Brunet stated that Wolpoff and colleagues had provided no evidence that the skull was that of an ape, and nor had they disproved any derived feature that this species shared with later hominids.

This area of science is known to be fiercely competitive, with each new discovery received with cool scepticism by the rival research groups, all of whom are digging in different parts of Africa. In January 2001, it was Senut and Pickford who had to face the doubters when they announced the discovery of Kenyan fossils - a piece of jaw, teeth, a fingertip, an arm, and a sturdy leg bone - which they said came from a six million year-old hominid (Orrorin tugenensis).

It is the journals and the process of peer review that have to try to balance various claims and counter claims and steer the science towards a clearer understanding of the origins of the human race. Chris Stringer, a hominid expert at London's Natural History Museum, said that whatever the truth about Sahelanthropus, it was still a find of great importance.

Patchy state

He pointed out the fact that Toumaļ was the only relatively complete skull discovered by this date which had originated from a period in prehistory that has produced very few specimens. And it was because of this 'fossil gap' that he cautioned all researchers not to make grand claims for any find.

In his opinion, it was still too early to say where either Sahelanthropus or Orrorin may lie in relation to our evolutionary line. The ancestors of the gorilla and chimpanzees remained to be recognised or found from six million years ago, no doubt along with parallel side-branches which probably also existed at that time.

It would be dangerous to assume that the present distinctive features of gorillas, chimpanzees, or humans would necessarily have been present at the beginnings of their evolution, or were unique to their line only. It would also be premature to push the claims too far for any fossils to be the earliest members of the human family in the present patchy state of our knowledge.

Mark Collard, an anthropologist from University College London, was of the same opinion. At this point in time he didn't think that there was any reason to accept either team's hypothesis. We could be confident that the specimen was certainly a member of Hominoidea (the group formed by hominids and apes), but at the moment, in 2002, Toumaļ could not be classified as a hominid or an ape with any certainty at all.

Hominid tree
Complex hominid tree

Scientists are having difficulty working out how the different hominids relate to each other

 

 

     
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