human evolution

15 July 2017: New dates for Homo naledi and (surprise!) new dates for H. sapiens

I originally intended to write about how recent dates discovered for Homo naledi meant that it and H. sapiens, our own species, had only the narrowest window in time to cross paths, but recent finds in Morocco have put paid to that. The announcements of the two sets of dates occurred within days of each other, and demonstrate just how quickly our knowledge of early human evolution is itself evolving.

Homo_naledi_holotype_specimen_(DH1)

Holotype specimen of H. naledi (Photo: Lee Roger Berger research team)

The new information for H. naledi appeared in three papers published in eLife (here, here and here) in May 2017, and provided more detail about when this newly discovered species walked the Earth, as well as announcing the discovery of a second area – the Lesedi Chamber in the Rising Star cave system about 50 km northwest of Johannesburg in South Africa – containing yet more H. naledi remains.

(For more on the first discovery, see in an earlier blog the interview I did with Elen Feuerriegel, one of the ‘underground astronauts’ involved in the recovery of the H. naledi remains in the Dinaledi Chamber).

Morphologically, the new species contained features that positioned it somewhere between the Australopithecines and the early members of our own genus, Homo; this would place it somewhere around two million years old. Confusingly, however, the bones found in the Dinaledi Chamber were still made up of hydroxylapatite, a form of calcium that takes up around 70% of the weight of human bones. Normally, fossilization results in the hydroxylapatite being replaced by minerals like silica. This suggested a more recent existence for H. naledi.

And the bones spoke true. The new papers give dates for the remains that placed it between 335,000 and 236,000 years old. Since the conservative dates for our own species up to May were 190,000 years ago, or 260,000 if you count the Florisbad skull as belonging to our own species instead of another such as H. heidelbergensis, it seemed unlikely, if remotely possible, that our ancestors crossed path with H. naledi.

But then came the second announcement.

A paper published in Nature in June 2017 revealed that H. sapiens remains discovered at a cave called Jebel Irhoud in Morocco, approximately 100km west of Marrakesh, and retrieved largely during the 1960s, have now been dated to extend as far back as 300,000 years, pushing it way beyond Florisbad and well within reach of H. naledi.

Jebel_Irhoud_1._Homo_Sapiens

Irhoud 1(Photo: Ryan Somma)

The skulls among these finds are not shaped like modern human skulls; the remains were originally classified as belonging to a sort of African Neanderthal. But the faces are flat, like our own, without the prominent inflated brow ridge of Neanderthal.

Where exactly they lie in the long line of human evolution is not known for certain, but their location and their age suggest strongly that they are archaic H. sapiens and not some other species.

While this does not change the overall pattern of human evolution as currently understood, it does dramatically extend the time that our species has existed, and strengthens the argument that the cradle of modern humanity was indeed Africa.

08 May 2917: Update on Homo floresiensis

Since my last blog on Homo floresiensis almost a year ago, two new discoveries have pushed back the origin of the species to at least 700,000 years ago and clarified its line of descent.

The original remains were found in Liang Bua cave on the Indonesian island of Flores in 2004. A short hominin that stood about a metre high, almost inevitably the new species was dubbed the ‘Hobbit’.

H. floresiensis

Homo floresiensis almost certainly not descended from …

There was initial controversy in some corners about whether the remains represented a new species or diseased specimens of Homo sapiens. Mounting evidence that it was indeed a new species climaxed with the announcement in June 2016 that fossils found in the So’a Basin of central Flores in 2014 possess characteristics that are morphologically similar to those found in Liang Bua fossils.

At 700,000 years old, these new fossils are the most ancient hominin remains yet found in Flores, and strongly suggest the ancestors of H. floresiensis first reached the island long before anatomically modern humans had evolved in Africa.

The main debate subsequently shifted to whether or not H. floresiensis was descended from Homo erectus – whose fossils were first discovered in Java – or some other early hominin.

H. erectus

Home erectus, but possibly from …

If descended from H. erectus, the Hobbit was an excellent example of ‘island dwarfism’, where populations of larger animals restricted in geographical range – usually islands – decrease in size over time. (Ironically, smaller animals in the same situation, lacking predators, tend to increase in size.)

A new paper published in the Journal of Human Evolution in April this year, however, presents strong evidence that H. floresiensis most likely descended from an earlier hominin. In the words of the authors, the results of their research indicates it is ‘a long-surviving relict of an early (>1.75 Ma) hominin lineage and a hitherto unknown migration out of Africa … ’

H. habilis

Homo habilis.

Using Bayesian phylogenetic methods and ‘parsimony’, the authors conclude that H. floresiensis is sister either to H. habilis alone or to a clade consisting of other hominin species including H. erectus and H. sapiens. However, they point out that a close phylogenetic relationship between H. floresiensis and H. erectus or H. sapiens can be ruled out.

These findings are important for two reasons.

First, they should finally put paid to any theory that the Hobbits are simply pathological specimens of our own species.

Second, it suggests that our hominin ancestors were migrating from their African homeland long before Home ergaster – the probable ancestor of H. erectus and sister species – decided to emigrate to pastures new some two million years ago.

Wanderlust, it seems, is an essential part of our genetic makeup.

22 May 2016: Crows got smarts

Corvus_corax_tibetanus

Corvus corax, the common raven. Photo: Pkspks [CC BY-SA 4.0]

It’s no secret that corvids – crows and ravens – are exceptionally smart for birds, especially at problem solving. Now an experiment carried out with ravens provides evidence they may have a basic Theory of Mind as well; this means they have an ability to attribute mental states they experience to another raven.

In a paper published in Nature in February, researchers Thomas Bugnyar, Stephan Reber and Cameron Buckner from the universities of Vienna and Houston, carried out an ingenious experiment that tested how ravens caching food behaved when they thought they were being seen by another raven.

There is increasing evidence that the Theory of Mind exists in chimpanzees, bonobos, scrub jays and ravens. How equivalent the experience of a ToM is between species is, so far, untestable, but the strong possibility that some form of ToM exists in different animals provides yet more evidence of the complexity of the mental life of species apart from humans.

Not only does this add weight to calls that humans should reconsider the way they relate to other animals, especially the often appalling way we treat farmed and domesticated animals, but firmly places Homo sapiens as the product of the same evolutionary process that produced ravens, dogs and garden slugs.

16 May 2016: New dates for the ‘Hobbit’

Homo floresiensis

Photo: Ryan Somma

Updating my blog celebrating the 10th anniversary of the discovery of Homo floresiensis, better known as the ‘Hobbit’, a letter in Nature has revised the most recent dates for the remains from 12,000 years back to 60,000 years. The sediment layers in the cave of Liang Bua on the Indonesian island of Flores, where the remains were discovered, had not been laid evenly, leading to an initial miscalculation.

Stone artefacts attributed to H. floresiensis are dated more recently, to 50,000 years ago.

The biggest implication of the new dates is that it is now less likely that the ‘Hobbit’ coexisted at the same time as H. sapiens on Flores. Although it cannot be ruled out, the earliest dates for human occupation at Flores is 50,000 years, leaving a very narrow window of opportunity.

11 February 2016: Digging for relatives

DSC02344

Elen Feuerriegel with thermoplastic copy of H. naledi lower jaw.

“Sometimes I can’t believe it happened,” said Elen Feuerriegel as the 3D printer by her side chugs out a thermoplastic copy of the cranium of an ancient human.

“I’m doing something ordinary, something I do every day, and then remember that two years ago I was working 30 metres underground recovering the remains of Homo naledi, a previously unknown human species.”

Feuerriegel, a PhD student in palaeoanthropology at the Australian National University, was one of six excavators – dubbed underground astronauts by an excited media – who retrieved the bones of up to 15 individuals from a small and almost inaccessible cave.

Part of an expedition organised by Professor Lee Berger from the University of Witwatersrand to investigate the Rising Star Cave in South Africa, it was the task of the Feuerriegel and the other five excavators to reach a small and unmapped annex to the cave system called the Dinaledi Chamber.

“To get to the chamber meant worming our way through a fissure that in one place narrowed to just 18 centimetres,” Feuerriegel said. “The fissure itself was a 12-metre drop that ended in a tiny landing, followed by another four metre drop to the floor of the chamber.”

What Feuerriegel first saw there will stay with her for the rest of her life.

“It was a wonderful, exhilarating experience. It was incredible amount of fossil material in one place. It was almost impossible to move without stepping on a jaw or leg bone.

“As our eyes got used to the dimness and we became more experienced at discerning fossils in the floor sediment, new finds seemed to appear out of nowhere.”

Despite her interest in science starting as a young teenager, her appearance at the Rising Star Cave System was never a given. She reached palaeoanthropology through a route almost as torturous as the entrance to the Dinaledi Chamber.

“My first love was marine biology, particularly sharks. That somehow morphed into a fascination with volcanoes. Then my mum, an information architect, helped me put together a web page for a school project I did on human evolution.”

Feuerriegel speaks about evolution through natural selection with a focused passion.

“For me, evolution is the great leveler. We humans are as subject to evolutionary forces as other species.”

The American crime procedural CSI: Crime Scene Investigation also stirred in her an interest in anatomy.

She did her first degree in sociocultural anthropology at the University of Queensland. “I’d given up on the idea of palaeoanthropology until I did an intensive summer course on human evolution.”

With an honours degree in her pocket, Feuerriegel came to the ANU to do her masters, and in 2013 began her PhD in palaeoanthropology.

Later that year, Lee Berger put the call out for people with a special and unusual skill set.

“He wanted skinny palaeoanthropologists who were also experienced climbers or cavers.”

Feuerriegel, who enjoyed wall-climbing and hiking, and had previously worked in a mine shaft in Sima de las Palomas in Spain looking for the remains of Neanderthals, applied for one of the openings.

Underground astronauts

The Underground Astronauts: Becca Peixotto, Alia Gurtov, Elen Feuerriegel, Marina Elliott, K. Lindsay Hunter, Hannah Morris. Photo: John Hawks

“Despite the specialist skill set, there were 60 applicants. I was one of six chosen.”

Within three weeks of an online interview, Feuerriegel found herself in South Africa retrieving the remains of a new human species, Homo naledi.

“We worked in two shifts, each with three excavators and two support cavers. Each shift lasted anywhere between three and six hours, depending on the task. The expedition tried to get at least two shifts down in the chamber every day, and sometimes three.

“For the first few days it could take up to an hour to get down from the surface to the chamber, but by the end of our stay there we’d reduced that to 20 minutes, giving us much more time for the real work.”

Towards the end of the work, seasonal rains raised the water table.

“There was no danger to us – the site was well above the water table – but conditions gradually got worse and surfaces more and more slippery.”

In the end, the excavators recovered the remains of 15 individuals, male and female, ranging in age from neonatal to an older female with very worn teeth.

Feuerriegel said she’s sure what the team discovered is a new species of ancient human.

“Morphologically, Homo naledi sits somewhere in the bridge between the latter Australopithecines and the early Homo, having features of both as well as some unique features all of its own. Exactly where it fits is something we don’t know yet.

“The other thing we don’t know at this point is how old the remains are. The bones we found had not yet been replaced with minerals like silica, but were still made up of hydroxylapatite, a form of calcium.”

She said if the remains proved to be between two and three million years old, H. naledi is the earliest definite example of Homo with skeletal material representing the whole body.

“If the remains are between one and two million years old, the date’s about right for a hominin of H.  naledi’s morphology.

“And if the date is less than one million years old, it means we have multiple species of hominins existing at the same time in South Africa. In that case, H. naledi’s small braincase and primitive morphology must make us seriously reconsider what it means to be a member of our own genus.”

Early reaction among some palaeoanthropologists hasn’t been all positive.

“Claims that the remains represent an early form of Homo erectus are fanciful,” Feuerriegel said. “A lot of critics have also focused on Lee’s description of the appearance of the bodies in one place as ‘ritual’.

“In this case, we aren’t suggesting anything spiritual, only that it represents repeated and deliberate behaviour.”

One of the career highlight for any palaeoanthropologist is to be one of the official ‘describers’ of a new species; thanks to her time in South Africa, Feuerriegel, at the age of 26 and still at least six months from finishing her PhD, is one of the names on the scientific paper officially naming the new species.

“I’ll also be lead author on a paper describing H. naledi’s upper limb, an area of morphology I’m particularly interested in.”

Feuerriegel said humans hold themselves on a pedestal as a species, above and apart from our ancestors.

“If there’s one thing H. naledi illustrates, it’s that the characteristics and behaviours we believe make us unique are not so unique after all.”

31 October 2014: Homo floresiensis, aka the Hobbit, now 10 years old

It wasn’t as momentous as Copernicus displacing Earth from the centre of the universe, or Darwin displacing humans from the centre of creation, but ten years ago a team of Australian and Indonesian palaeontologsits announced a discovery that changed the way scientists view not just the history of humans, but the history of the entire human clade. If Darwin’s On the Origin of Species started an earthquake, then the discovery of a recently extinct tiny-limbed and tiny-brained human on the Indonesian island of Flores started a serious tremor.

The waves from that tremor are still rippling through palaeontology. Some scientists argue that the new human, dubbed Homo floresiensis but more often referred to as the Hobbit in popular media, is nothing more than a diseased remnant of an isolated population of modern humans. It does seem, however, that proponents of this hypothesis are increasingly desperate to prove their case. The most recent argument is that the remains display classical symptoms of Downs syndrome. I’m still waiting for them to wheel out childhood smoking as the cause for the Hobbit’s miniature status.

It seems to me that the weight of evidence is overwhelmingly on the side of Homo floresiensis being a new member of the human family. It has no chin, its leg bones are unusually thick, and its wrist bones more closely resemble those of an African ape or group of ancient humans called Australopithecines.

Another piece of evidence that H. floresiensis was not a dwarf or diseased version of H. sapiens is the stone implements found with the remains. These tools are the size you’d expect them to be if made by and for humans around a metre tall. More importantly, they and the bones were found in strata laid down as long ago as 95,000 years ago. Modern humans did not arrive in Indonesia until about 45,000 years ago.

The great mystery surrounding H. floresiensis is where exactly it fits in the human clade. Most evidence suggests it is a very primitive member of the genus Homo, but perhaps, just perhaps, it belongs in the group of Australopithecines with A. afarensis and A. africanus.

The one outstanding fact about this tiny cousin of ours is that it may have survived at least until 18,000 years ago, and possibly even as recently as 12,000 years ago. The Neanderthals, our closest relative among all the species of humans that have walked the Earth, died out not later than 35,000 years ago.

Homo floresiensis was a true survivor.

[For more information about the discovery of the Hobbit, go here. For more information about the history of the debate on whether or not the Hobbit is a new species, go here.]