A New Man – The mystery of Homo naledi

Artists reconstruction of Homo naledi from the skeletons found

Last week, University of the Witwatersrand anthropologist Lee Berger announced the discovery of a new species of hominid – Homo naledi.  It followed his remarkable discovery of Australopithecus sediba some years before, but this discovery is widely regarded as still more significant and surprising.

A selection of the remains

Naledi – a star in the Sesotho language – is an extraordinary creature, somehow mixing features of Australopithecus and Homo.  The skull is really small—the brain was about the size of an orange—yet adult individuals were comparatively large at around 5 feet and 100 pounds. The hands share many of the features of our own, yet the fingers curl and the shoulders slope which is more characteristic of the Australopithecines who were probably tree climbers.  The feet are quite similar to ours and the legs are long, suggesting that naledi walked and ran in a similar way to us, and spent much time on the ground.  If you would like to read a much more in depth account, Homo naledi makes the cover of National Geographic next month and you can preview the article HERE.

So then is naledi claimed as the so-called ‘missing link’ between Australopithecus and Homo?  Is South Africa—indeed Johannesburg!—truly the ‘cradle of humankind’?  The answer is no, or at least not yet.  The missing piece of information is age.  So far no one has been able to determine the age of the fossils from the Cave of Stars.  And the age options for naledi are truly fascinating.

Researchers at the Dinaledi cave

If nadeli is more than 3 million years old, then Australopithecus was just a side bar; Homo had evolved from something else already. Naledi would probably be our ancestor. Yet the similarities of certain features to each genus suggest rather an age of between two and two and a half million years and then naledi could indeed be the link between the two genera. And if naledi is younger still—less than a million years, say—then there were at least two very different species of Homo living in Africa at the same time.

The discovery of the fossils was made about two years ago almost by accident at a cave near the Cradle of Humankind some 30 miles north west of Johannesburg.  Two amateur speleologists were exploring a popular cave system and one came upon a hidden tunnel dropping steeply downward. The two of them were looking for something new and exciting, and decided to take on this chimney.  At the bottom they found a treasure trove of fossil hominid remains.

Lee Berger and his new friend

I said the discovery was almost by accident, but Professor Berger had gone to a lot of trouble to get the word out to keep an eye open for interesting fossils in the area, and that made the link.  The two cavers brought him their news and pictures, sparking off the discovery of the largest collection of hominid fossils ever found in Africa. Realizing he had to act quickly, Berger assembled a team of volunteers who were brave enough and slender enough to get into the chamber.  He called them his cave astronauts and all of them are women. Already more than 1500 individual fossils have been collected and come from at least fifteen different individuals of various ages.  Also amazing is that the fossils are almost exclusively human, apart from a few birds and rodent-like creatures.  This is not a cave full of victims of some predator; the bones are unmarked by teeth. And there is no sign of a river washing the fossils into the cave as then there would be an appropriate mix of other materials.  No, these creatures are alone in the dark.  How did that happen?

Watch Lee Burger giving a fascinating summary HERE.

The Dinaledi 'astronauts'

For all the excitement about a new man, the most fascinating part of the whole story is that naledi apparently disposed of its dead; indeed the Dinaledi cave seems to be a graveyard.  Until now there has been no suggestion that any species other than Homo sapiens took pains to remove the bodies of the dead from the natural environment, certainly not by following a difficult route into a hidden chamber to leave them there.  But the scientists have considered every other reasonable possibility and rejected it by careful argument.

“When you have eliminated the impossible,” Sherlock Holmes once observed to Watson, “whatever remains, however improbable, must be the truth.”  Professor Berger rather charmingly misquoted this at the press announcement as “When you have eliminated all the probable, you are left with the impossible.”  Various people have vehemently agreed with that judgement!  On the one hand, some scientists have rejected his conclusions and insisted that there must be other explanations, while at the other extreme the whole scenario is rejected by creationists with one even describing the discovery as a white racist plot designed to keep black people at a subhuman status. (How this argument could possibly be made is beyond me; indeed the Wits Vice Chancellor, Professor Habib, pointed out at the press announcement that the implications of all humans arising from a common ancestor emphasises our similarities not our differences.)

But in the scientific community there seems to be no disagreement that we have just met an ancient member of our genus, never before even suspected.  And the mystery of when they walked the earth remains.

Ex Africa semper aliquid novi.

Michael - Thursday

The Naked Cook

I am arguably the world’s worst cook, so I avoid it as much as possible.  I do, however, love to eat good food, and I suppose I always thought that the purpose of cooking was to turn tasteless and chewy raw ingredients into something delicious.  To the extent that I thought about it at all, I assumed that cooking was something that developed somewhere in our evolutionary past when one of our distant ancestors dropped a chuck of raw meat into the fire and it took him a while to fish it out.  I visualized a Neanderthal or the like doing this.  

Maybe this just displays my general ignorance.  Recently, on a long plane trip, I read a book that had a very different interpretation of events and one I found fascinating.  It’s an African story; wherever this happened, it was somewhere in Africa. And with the Cradle of Humankind up the road from where I live, it might have been quite close by.

The book is CATCHING FIRE: How cooking made us human by Richard Wrangham. The author is the Ruth Moore Professor of Biological Anthropology at Harvard and an expert on Chimpanzees on the side. This guy knows his stuff. It is sometimes said that we are what we eat. The thesis of this book is that it’s not what we ate that mattered, but that we cooked it first.

Professor Wrangham and friends
Compare the teeth!

The book starts out gently explaining that raw food is great except that it takes a long time to chew up and a lot of energy to digest.  Much of the food value is wasted. What you need is big, strong teeth, heavy jaw muscles, and plenty of lower intestine.  My neighbors up the road here had all that. They were much smaller than humans but had bigger teeth.  I did know that.  I suppose I just thought that our smaller teeth resulted from our larger overall size and changed diet.  Well, right.  Professor Wrangham points out that it's diet that drives evolution, never the other way around.  It was when our ancestors started cooking their food that two things happened, probably over quite a short space of time in evolutionary terms.  The one was that they were now getting much more nutrition from the same amount of food. That’s because breaking down the cellular structure with heat makes the nutrients more easily accessible. The other was that we could eat more quickly. The food was softer, less chewing was required, and less digestion.  Over time our teeth changed to reflect that situation and our guts changed appropriately too.

Australopithecus Sediba

The archaeological record shows that humans controlled fire about half a million years ago and maybe much earlier. At Swartkrans in South Africa and at locations in Kenya, there are sites dating back one and a half million years with suggestions of fire use. This physical evidence is disputed so Wrangham turns to biology instead, seeking the change in anatomy that would link with the cooked food.  

Over the last two million years, there were only three periods when our ancestors’ evolution was fast and strong enough to justify a change in species names.  The crucial one occurred some 1.8 million years ago when Homo erectus emerged from the australopithecines.  ‘Suddenly’ we had a much larger creature, one that walked and ran and was probably not well suited to climbing, had smaller teeth, and probably differently structured guts.  It had to be fire that allowed the erectus part.  The African savanna was not a safe place to be on the ground at night with saber tooth cats all over the place.  The australopithecines were probably excellent climbers and slept in trees as all modern apes do.  But if you were cooking around a cheerful bonfire, sleeping around it – presumably with a watchman to keep the fire fed – would be safe and comfortable.  So the implication is that it was the possession of fire and the rudimentary art of cooking that drove the development of Homo.

Skull of Homo Erectus

That in itself is a pretty intriguing idea.  But there’s more.  If we were happily eating roasted meat and broiled vegetables all that time ago, why did our brain size develop?  It turns out that the development of brain tissue is very expensive in terms of energy demands. Wrangham believes that what we think of as intelligence was needed for social interaction rather than for food gathering.  It was the excess of nutrition from the cooked food that allowed the extra resources to feed and develop our brains. Thus it was cooking that led to our intelligence, rather than the other way around.  

Wrangham has one final twist. He observes that universally in hunter-gatherer communities, the women do the cooking. (The exceptions are a few instances when men do some culturally significant form of cooking and he dismisses those.) Men do the hunting – or whatever else they want to do – and leave the vital cooking task to the women.  In a few societies, it's much more significant for a woman to feed a man than to have sex with him.  If she gives him dinner, they're married.

Wrangham toys with the idea that as cooking developed, females could be set upon and have their food stolen, so they made alliances with males, not for sex and procreation as is the conventional wisdom – generally apes don't do that - but for shared food and resources and for defense against food thieves.  So much for ‘family values!’  It’s all about food!  Wrangham obviously feels very uncomfortable that this prehistoric motivation has settled into modern times as an excuse give women a subservient role.  He concludes this chapter with:

 “The idea that cooking led to our pair-bonds suggests a worldwide irony. Cooking brought huge nutritional benefits. But for women, the adoption of cooking also led to a major increase in their vulnerability to male authority. Men were the greater beneficiaries. Cooking freed women’s time and fed their children, but it also trapped women into a newly subservient role enforced by a male dominated culture. Cooking created and perpetuated a novel system of male cultural superiority. It is not a pretty picture.”

Michael - Thursday