human evolution

24 August 2018: When did humans first leave Africa?

This blog post is titled ‘When did humans first leave Africa?’ I confess, it’s a trick question, but we’ll come back to that later.

So to start with, let’s attempt to answer not a trick question but a trickier question: when did Homo sapiens first reach Australia?

This has been a contested debate for several decades, with proposed dates stretching from 75,000 years ago to 40,000 years ago. The bottom mark was established by the dating of the remains of Mungo Man, the oldest remains  of anatomically modern humans (AMH) yet found outside Africa.

Mungo Man

Mungo Man

Towards the upper end, luminescence dating of sediments around artefacts recently found at Madjedbebe in the Northern Territory give a date of around 65,000 years, although this is contested.

In a recent article in The Conversation, ‘When did Aboriginal people first arrive in Australia?’, authors Alan Cooper, Alan N. Williams and Nigel Spooner state the ancestors of Aboriginal Australian first reached Australia sometime between 50,000 and 55,000 years ago, just after AMH left Africa.

This date comes from geneticists working on Neanderthal ancestry in the modern human genome. In ‘Tracing the peopling of the world through genomics’, authors Nielsen et al. write that:

‘All non-African individuals studied so far contain around 2% Neanderthal ancestry, suggesting that admixture mostly occurred shortly after the dispersal of anatomically modern humans from Africa … the date of hybridization has been estimated to be approximately 50–65 kyr ago …’

33.1 H. neanderthalensis Amud 1 0.4-0.04 mya

Cast of H. neanderthalensis (Amud 1) from the Australian National University. Photo: Simon Brown

This date is now generally accepted by palaeoanthropologists.

But that presents us with a quandary. As I wrote in an earlier blog, fossils from the cave of Jebel Irhoud in Morocco, together with genetic data from a 2,000 year old Khoe-San skeleton, suggests our species arose in Africa at least 300,000 years ago. So why did it take our species a quarter of a million years to find the exit?

Well, as it turns out it, it didn’t.

In a January 2018 report in Science, authors Chris Stringer and Julia Galway-Witham note that recent fossil evidence from Israel suggests our species had left Africa by 180,000 years ago. The report also recounts genetic analyses of Neanderthal fossils from two caves, Denisova in Russia and Hohlenstein-Stadel in Germany, that ‘indicate at least one earlier phase of introgression, from H. sapiens into Neandertals … estimated at 219,000 to 460,000 years ago’.

At this stage, it seems that AMH could have left Africa over 200,000 years ago, and yet DNA evidence strongly suggests the ancestors of all non-African members of our species left Africa no earlier than 60,000 years ago.

So what’s going on?

Nielsen et al. write that the latter date indicates when the ‘ultimately successful’ dispersal of H. sapiens from Africa occurred. In other words, those members of our species who left earlier are now extinct and left no trace in our genetic record.

Stringer and Galway-Witham write that there is evidence there were several humid phases between 244,000 and 190,000 years ago. But these phases were bracketed by severe periods of aridity, which meant ‘the region was probably more often a “boulevard of broken dreams” than a stable haven for early humans.’

Chris Stringer

Chris Stringer, Research Leader in Human Origins, Natural History Museum

On the other hand, a letter published in Nature in 2016 suggests that earlier migrations of H. sapiens from Africa may have left their mark on some of us after all; specifically, Papuans.

After analysing ‘a dataset of 483 high-coverage human genomes from 148 populations wordwide … ‘ Pagani et al. found ‘ … a genetic signature in present-day Papuans that suggests that at least 2% of their genome originates from an early and largely extinct expansion of anatomically modern humans … out of Africa.’

This brings us back to the article in The Conversation. Cooper et al. discuss how Aboriginal Australians moved to and occupied Australia around 50,000 years ago. Of course, 50,000 years ago it wasn’t Australia, it was Sahul, a single landmass comprising Australia, Tasmania and Papua New Guinea.

Sahul

Sahul

Yet the letter in Nature suggests that Sahul might in fact have been occupied by H. sapiens before that date. Its authors hypothesise either that these people came from an unsampled archaic human population that split from modern humans ‘either before or at the same time as did … Neanderthal’, or that they were a modern human population that left Africa ‘after the split between modern humans and Neanderthals but before the main expansion of modern humans in Eurasia’.

The data from all this research is sometimes confusing and contradictory. Over the last quarter century palaeoanthropology has undergone a great revolution driven partly by discoveries of new hominin fossils (eg H. floresiensis and H. naledi), and partly by new and refined techniques in analysing DNA. There is a lot of data to sort through, doublecheck and assess. Nevertheless, as measurements are refined and new discoveries are made, we learn more about our past and so more about ourselves.

#

So, why is the header a trick question?

H. habilis

Homo habilis

All the above information deals with the history of just one species, our own. But H. sapiens were not the first humans to leave Africa. For example, some members of H. heidelbergensis left Africa around half a million years ago, evolving into H. neanderthalensis in Europe. Those that remained in Africa almost certainly gave rise to H. sapiens.

And if the conclusions of a recent paper by Argue et al. studying the phylogeny of H. floresiensisis are correct, then another and possibly earlier human migration out of Africa occurred. This species’ forebears are closely related to H. habilis, the oldest species in our genus, Homo.

It’s almost as if the need to migrate is as defining a feature of our genus as bipedalism, a large brain and an opposable thumb.

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14 December 2017: Colin Groves (24 June 1942 – 30 November 2017)

1

My friend Colin Groves died two weeks ago this day. It came a surprise, although I knew he was in palliative care. He seemed invincible as those with a great intellect always seems invincible, as if death could be put off indefinitely. Although aged he was never an old, and although physically ill his mind was as sharp as an Acheulean hand-axe.

In a real sense his work makes him immortal, at least as far as any human can be immortal. I knew him chiefly as a friend and fellow skeptic, and more recently as a co-writer. Although I had some knowledge of his standing among taxonomists, anatomists, biological anthropologists, primatologists and palaeontologists, he was overwhelmingly modest. Just the preceding list of fields should give you some idea of the breadth of his knowledge.

When Jane Goodall was asked what it felt like to be the world’s foremost primatologist, she replied ‘You’re mistaken. The world’s foremost primatologist is Colin Groves.‘[i]

At his funeral, colleague Professor Kristofer Helgen noted that Colin had named more than 50 new kinds of mammals, and that the first, the Bornean Rhino, remains the largest living mammal described in recent generations.[ii]

‘Colin was the most influential large-mammal taxonomist of the last half-century. His discoveries and impacts are astonishing … The last species he named, in a paper which appeared … in the last month of his life, was the Tapanuli orangutan, one of only eight living great apes on our planet … ‘

As Professor Helgen points out, Colin is probably best known for describing Homo ergaster in 1975, together with Vratislav Mazák. Homo ergaster, which lived in Africa between 1.4 and 1.9 mya, was probably one of our direct ancestors.

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Homo ergaster. ANU cast of cranium KNM ER 3733, discovered at Koobi Fora, Kenya, in 1975 by Bernard Ngeneo.

Professor Helgen said Colin Groves was an original.

‘He was a gentle soul, but could be an immovable opponent. And he was genuinely brilliant, yet every bit as genuinely modest … When I think of Colin, I see him in my mind’s eye in his office at the ANU, decked from floor to ceiling with books and journals and reprints, all of his key resources, usually reckoned obscure to all others, within arm’s reach.’

This rings a cathedral of bells. Whenever something came up in our conversation about – well, almost anything – Colin would have a book, journal or anecdote to clarify, correct or corroborate any fact, no matter how obscure.

But my overriding memory of Colin isn’t his intellect or reputation, but his enormous kindness and placidness. He was never overtaken by anger, only bewilderment at the occasional fecklessness or waywardness of his fellow Homo sapiens.

He was one of my dearest friends, and his passing leaves a gaping hole in the lives of everyone who knew him.

Below is the eulogy I delivered at his funeral last Thursday.

Colin Peter Groves

As I look up at the Canberra’s first blue sky in five days, I’m tempted to think that while Colin did not believe in god, god almost certainly believed in Colin.

Although I knew him for 30 years it wasn’t nearly long enough, but perhaps long enough to discern the three great loves of his life.

Most importantly of all, his partner, best friend, constant companion and carer, Phyll.

Second, his love of science, particularly biology of course, and how it revealed to him the universe he shared with his fellow-primates, ungulates, big cats, avian dinosaurs, tardigrades, dogs, bats and cetaceans.

Third, his love of chinwagging. All the creatures I just mentioned could happily be included in a single lunchtime conversation with Colin. You might start discussing sexual dimorphism among species of African antelope and end by discussing the size of Donald Trump’s genitalia. (Amazingly, and somewhat distressingly, size does matter in nature.)

Let me deal briefly with each of these three great loves, from last to first.

It seemed to me that Colin was in his element when he shared conversation with friends and colleagues. If food and drink were included, so much the merrier, which added a cruel twist to the illness that eventually took him from us.

Although most discussions started with and usually revolved around science, his interests were catholic: skepticism, history, music, art, literature, film and television, and a hundred other subjects. He didn’t possess a ‘comfort zone’ as such; he was happy drifting on a sea of titbits, anecdotes, quotes, and bad puns (because, as Colin would patiently explain, a good pun isn’t a pun but a joke, and the quality of a pun is directly proportional to the volume of the groan it elicits).

He also had a deep and abiding love for startling and unexpected facts.

I remember how much he enjoyed discovering that the Great Pyramid of Khufu, built around 2560 BC, was the tallest building in the world until succeeded by – of all things – Lincoln Cathedral in 1311. A 3,800-year old record. He was just as delighted to learn that when Lincoln Cathedral’s centre spire collapsed in 1549, the Great Pyramid couldn’t resume its title as the world’s tallest building because erosion had reduced its height to below that of a church in Germany.

While an hour’s conversation with Colin could be filled with minor revelations such as these, they were never random thoughts. They were either staging posts that guided you safely to the end of a conversation, or points that illustrated a greater truth Colin was pursuing with the gentle doggedness of a modern-day Socrates.

In a conversation about intelligence and self-awareness, he might include the latest research about the Theory of Mind among corvids, Mozart’s Marriage of Figaro, gorillas studying their reflection in mirrors while trying on different hats, and the British television series Peaky Blinders. But every diversion would have a point, and every point would add weight in support of an argument for or against a main proposition.

I briefly mentioned Donald Trump. It seemed to me that while Colin never avoided discussing politics, what he cared about were the issues important to all of us in a free and democratic society, issues shaped and sometimes decided by politicians, pundits and lobbyists. It was people that Colin cared about, not cant. It was ideas Colin cared about, not ideology. What Colin wanted for our society was equality, opportunity, fairness and boundless curiosity.

Colin’s second great love was science, particularly anthropology and taxonomy. To say he was a biological anthropologist, while absolutely accurate, is entirely insufficient. Robert [Attenborough] has already talked about Colin’s amazing academic career, but I first met Colin because of his opposition to those forces that set themselves against science, particularly religious inerrancy, with a special focus on the shallow, silted stream of creationism.

From the first time I attended a meeting of the Canberra Skeptics, Colin immediately stood out as the most determined, the most knowledgeable and the most resilient opponent of creationism I have ever encountered. I never imagined someone as steeped in science as Colin would also be so utterly familiar with the Christian bible he could quote chapter and verse.

It wasn’t the idea of opposition that excited him, but the idea of investigating claims and when found wanting, standing up against them. I never once saw Colin angry, at least not in the sense most of us would understand the word, but when confronted by blind stupidity or blind faith, his eyes would open slightly in surprise, then narrow as he marshalled his arguments in defence of rationality.

The only other time I saw this response was when he was confronted by casual arrogance, wilful pride or careless prejudice. He understood how all these were used to stifle debate or to keep underdogs in their place, and he resented it.2

Colin was not a skeptic for the sake of it. It was just the flipside of the scientific method he applied to his everyday investigations of the natural world. It was as much a part of him as that sense of wonder that shone from him whenever he talked about the discovery of a new hominin fossil, or a new species of orangutan, or gravity waves.

Ultimately, forever and always, Colin’s greatest love was Phyll. On those few times I visited when Colin showed off just how much he knew about obscure science or history or culture, he wasn’t doing it to impress me. I think he was doing it because he just loved flirting with Phyll.

Phyll was his touchstone and keystone, his measure and the source of his strength. When she spoke, he listened. Even when he disagreed, he listened, and he listened closely.

And one never visited Colin, one always visited Colin and Phyll. They were as close to being a single unit as any two people I’ve ever met. Two minds, two voices, often two very different opinions, but a single soul, a word even Colin would agree with in this context.

They generously shared their life with family, friends, colleagues and students.

For that I will always be grateful.

[i] Mittermeier, Russell A. & Richardson, Matthew. Foreword to Extended Family: Long Lost Cousins, by Colin Groves. Conservation International, Arlington, 2008.

[ii] Helgen, Kristofer M. 2017. ‘Eulogy for Colin Peter Groves’, Canberra, 7 December.

09 November 2017: the eighth great ape and the problem with ‘species’

Until recently, only seven species made up the group of primates known as the great apes, or Hominidae. Two orangutan species (Sumatran and Bornean), two gorilla species (eastern and western), two chimpanzee species (chimpanzees and bonobos), and us.

But in a report recently published in Current Biology, an international team of scientists announced a new hominid with fewer than 800 members, Pongo tapanuliensis, found just south of Lake Toba in Sumatra. To save your tongue twisting around that particular binomen, we can call it the Tapanuli orangutan.

The scientists compared skull, jaw and dental characteristics of a Tapanuli specimen with those of the Sumatran and Bornean species, and analysed 37 orangutan genomes as a second line of evidence.

Orangutan

Three species of orangutan: from left, Bornean, Sumatran, Tapanuli. Photo credits: Eric Kilby, Aiwok, Tim Laman

The report gained a great deal of media attention: not only because we humans had a new cousin, but because the Tapanuli is an endangered species.

However, there were dissenting voices. In an interview with the ABC, for example, Lee Christidis from Southern Cross University pointed out that the analysis had been carried out on only one specimen and that the DNA evidence was at best ambiguous.

It’s only fair to point out that it’s often the case that a species will be described by a single representative organism, or, as happens frequently in palaeontology, those fragments of a single organism that have been fossilised or otherwise survived over many millions of years.

The report also generated discussion about what we mean by the word ‘species’. Jerry Coyne, professor emeritus at the University of Chicago and author of the excellent Why Evolution is True, wrote in his blog:

‘Not only do I see this new “species” as merely an isolated and genetically differentiated population (as are many human populations regarded as H. sapiens), but I’d also contend that there is only one species of orangutan overall, with these three groups all being subspecies. Sadly, a lot of systematists don’t see it that way, as they seem to think that any isolated population, if it can be told apart morphologically or genetically from others, warrants being named as a new species. Yet to evolutionists, a “species” is not an arbitrary segment of nature’s continuum, but real entities that maintain their “realness” because they don’t exchange any (or many) genes with other such entities where they cohabit in nature.’

But is this indeed the definition of species with the greatest currency among most biologists?

To start with, there has to a definition that works across all fields. A primatologist cannot have a different concept of species from, say, an entomologist, or the whole point of taxonomy – the orderly classification of living things that demonstrates their evolutionary relationships – starts to fall apart.

This doesn’t mean that definitions in biology – or any scientific endeavour, for that matter – are written in stone. As our knowledge of the world around us grows, the language we use to explore, explicate and explain that knowledge must also grow.

The definition I was taught at school is not dissimilar to Coyne’s quoted above, and is based on what is called the Biological Species Concept (BSC), developed by Ernst Mayr and Theodosius Dobzhansky in the early 1960s (Coyne did some graduate work under Dobzhansky at Rockefeller University). As Colin Groves, professor emeritus at the Australian National University, wrote, ‘This concept states that under natural conditions a species ‘should not exchange genes with other species’[i]. Groves goes on to point out that ‘ … the popular idea that two species are “unable” to interbreed is  a misunderstanding: it is not that they cannot interbreed, it is that they do not.‘

The BSC was further refined by Mayr and Jared Diamond in a paper on Melanesian birds in 2001, and then in 2004 by the aforementioned Jerry Coyne with H. Allen Orr in a book about speciation called, appropriately enough, Speciation.

Groves argues that the modified definition of BSC risks different standards of comparison in different taxonomic groups: it’s a definition that won’t work across different fields, in other words.

Groves again: ‘If a genus contains a pair of sympatric[ii] sibling species (species that differ only slightly, inconspicuously), the standard for species recognition will be set much “lower” than in a genus in which sympatric species pairs are grossly different. It is the search for objective standards – for an operational means of distinguishing species – that has been responsible for the controversies that marked taxonomic discussions over the past 15 or 20 years.’[iii]Taxonomy

Many biologists now use what is called the Phylogenetic Species Concept (PSC), developed by American biologist Joel Cracraft from the early 1980s. Put very simply, in this concept a species is the smallest population of organisms that is measurably different from other populations sharing the same ancestry. Note that this concept says nothing whatsoever about species sharing genes, such as happened between Homo sapiens and H. neanderthalensis around 100,000 years ago.

It’s important to note that both the BSC and the PSC are attempts to operationalise the evolutionary concept of species; that is, that a species is an evolutionary lineage.

While the report in Current Biology describing the Tapanuli orangutan as a new species of great ape has, for the most part, been received positively, the fact that many distinguished scientists question the findings shows that the debate about what constitutes a species is ongoing.

[i] Groves, Colin. ‘Speciation in hominin evolution’; African Genesis: Perspectives on Hominin Evolution; ed Reynolds, Sally C. & Gallagher, Andrew; Cambridge University Press; Cambridge; 2012, p 46.

[ii] Sympatry occurs when two or more species live in the same geographic area.

[iii] Ibid.

07 October 2017: New evidence suggest we are much older than 300,000 years

In a recent blog I wrote about new dates for skulls found in the cave of Jebel Irhoud in Morocco in the 1960s. Originally assessed as belonging to Homo neanderthalensis (an assessment that was soon challenged), a reappraisal published in Nature this year confirmed they were in fact H. sapiens skulls; the great surprise was that the reappraisal determined them to be at least 300,000 years old.

Jebel Irhoud

Cast of Jebel Irhoud 1 from the Australian National University. Photo: Simon Brown

New work done by scientists in Sweden and South Africa, and reported in Science, have now dated DNA obtained from a 2000-year-old Khoe-San skeleton apparently unmixed with Bantu or Eurasian DNA, as having separated from other H. sapiens sometime between 260,000 and 350,000 years ago.

The San are the First People of South Africa, Botswana and Namibia. Indeed, they may be the First People, the ancestral group all modern humans are descended from, or at the very least very closely related to them.

The San are the most genetically diverse of all humans living today. In an episode of Catalyst on the ABC about her research on San DNA, Professor Vanessa Hayes said, ‘There’s more similarity between myself and a Han Chinese than between two San people.’

Bushman

San hunter/gatherer

As reported in Science, the recent work on San DNA involved several ancient individuals, but the standout dates were given by DNA from the genome of a hunter-gatherer boy known as Ballito Bay A. The scientists concluded that, ‘ … our results show that the deepest split among modern humans (the estimated latest time for the emergence of H. sapiens) occurred at between 350 kya and 260 kya.’

Given that the skulls found in Morocco have been dated to at least 300,000 years ago, it would seem not unreasonable to consider the older dates for the emergence of H. sapiens – 350,000 years ago – being closer to the mark than the lower date of 260,000 years ago.

This new evidence also adds weight to the theory that our species may have partly evolved in South Africa.

In the last eight months, we have seen conservative estimates for the age of our species jump from 190,000 years old to almost double that. It’s been an extraordinary year for palaeoanthropology.

29 September 2017: What ancient hominid left her footprints in Crete?

There is strong evidence that a hominid walked in Crete in the late Miocene, about 5.7 million years ago.

In an article in the 31 August 2017 issue of the Proceedings of the Geologists’ Association, the authors describe the discovery in western Crete of tracks in rock accurately dated to the Messinian age. To quote the abstract, ‘The tracks indicate that the trackmaker lacked claws, and was bipedal, plantigrade, pentadactyl and strongly entaxonic.’

Trachilos footprints Andrzej Boczarowski

Ancient hominid footprints near Trachilos, Crete. Photo: Andrzej Boczarowski

In plain English, the authors are describing footprints impressed in rock that suggest the creature that made them walked on two feet, not four (bipedal), that it walked on its whole foot rather than just on its toes or claws (plantigrade), that it had five digits on each limb (pentadactyl), and that its big toe was bigger than its other toes (entaxonic).

In short, a footprint that resembles those that are left behind by hominins – the family of humans that includes you and me.

The paper caused a small storm in palaeoanthrapological circles for two reasons. First, there is little direct evidence anywhere of bipedalism before the Pliocene (the epoch immediately following the Miocene, starting around five million years ago), and second, there was no evidence of bipedalism outside of Africa before the Pliocene.

If the tracks discovered in Crete have been accurately dated, and the evidence seems strong on this point, then several intriguing possibilities present themselves.

First, that bipedalism, as palaeoanthrapological orthodoxy has it, evolved in Africa in a species that subsequently migrated to Eurasia (or possibly one of that species’ close descendants made the journey) much earlier than first believed.

Second, that bipedalism in our family may have evolved in Eurasia and not Africa.

Third, that bipedalism evolved more than once in our family. This would make it an extraordinary example of convergent evolution.

At this point, without completely discounting it, the first possibility seems the most unlikely, simply because there is no evidence – fossil or footprint – to support it. However, if this turns out to be the correct answer, a prime candidate would have to be Orrorin tugenensis, the oldest hominid for which we have strong evidence for bipedalism. Orrorin lived in Kenya in the late Miocene, so the dates fit.

The second possibility has been championed by scientists who think it may have been left by Graecopithecus freybergi, a hominin known by one mandible and a few teeth discovered in Greece. Although we do not know if Graecopithecus was bipedal, a recent paper proposed that its dental morphology suggests it is the oldest hominin and that therefore humans first appeared in Eurasia and not Africa.

Graecopithecus_tooth

Teeth from Graecopithecus freybergi

While this claim has been controversial, if Graecopithecus was the first hominin then it was almost certainly bipedal and may well have left impressions of its footprints in Crete. However, generally speaking dentition follows diet. Our teeth can evolve quickly to take advantage of new resources in food, so it is possible that despite its human-like teeth Graecopithecus was a hominid (a member of the family that include great apes as well as humans) but not specifically a member of the tribe Hominini. If this is the case, then Graecopithecus is only our distant cousin rather than an ancestor.

This leads to the third possibility, that bipedalism evolved more than once in the hominid clade. If this is the case, then there is one other strong Eurasian candidate for the owner of those footprints left behind in Miocene Crete, and some scientists think this candidate may have been bipedal.

Oreopithecus bambolii is known from 9-7-million-year-old fossils discovered in Italy from the 1870s. The best and most complete fossil was found in lignite, earning it the name of the Abominable Coalman.

For a long time the position of Oreopithecus in the hominid record has been controversial, most disagreement revolving around whether it is part of the ape or the human family.

Oreopithecus

Oreopithecus bambolii – the ‘Abominable Coalman’

Work done on Oreopithecus in the 1990s controversially proposed it was bipedal, although with a curiously positioned big toe that meant its foot may have acted almost like a tripod. This suggests it could walk on two feet, but probably not at any great pace.

A recent survey of the hominid’s spine, however, has led some scientists to think Oreopithecus was not fully bipedal. Furthermore, the footprints in Crete do indicate a more conventionally shaped foot.

The tracks were discovered in Crete, and dated to the Messinian age when the sea level of the Mediterranean was probably similar to now. Graecopithecus somehow would have had to make it across the equivalent of the Aegean Sea to reach Crete, and Oreopithecus across the Ionian and Aegean seas. Orrorin would have had to make it all the way from Africa. Of course, many animals throughout history have crossed seas and even oceans to reach isolated islands, including members of the hominid clade (Homo erectus to Java and Homo floresiensis to Flores, for example), but to date there is no fossil evidence of either Graecopithecus or Oreopithecus having lived – let alone walked – on Crete.

(This blog entry is based on an idea proposed by Colin Groves, Emeritus Professor of Bioanthropology at the Australian National University.)

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.