Four discoveries that redefined human history in just one summer

Growing up in a more literarily and theologically inclined family, much of my paleoanthropological education came from back issues of National Geographic and outdated editions of Encyclopædia Britannica. I read Mary Leakey’s article about her discovery of the footprints at Laetoli in the April 1979 issue, and pored through earlier issues to find articles about her work at Olduvai Gorge — articles like one from October 1961 by her husband Louis S. B. Leakey titled “Exploring 1,750,000 Years into Man’s Past: A Noted British Archaeologist Tells of Dramatic Discoveries at Olduvai Gorge.” I desperately wanted to be a young Leakey boy like (future paleoanthropologist) Richard or (future statesman) Philip, seen with his parents in this photo from that article. Frankly, I’d have settled for being one of Mary Leakey’s ever-present dalmatians.

Photo: National Geographic

It seemed like every issue in the 60’s and 70’s highlighted some amazing discovery that reshaped our understanding of how our species emerged in Africa. As I’ve re-engaged with archaeology and human evolution over the last few years, at no time has there been such a rapid sequence of major announcements from across a spectrum of disciplines, based on work happening all over the world, as there seems to be right at this very moment.

With stacks of books about Neanderthals representing decades of perspectives as a lens into the historiography of paleoanthropology, I’ve most enjoyed learning about how our understanding of human evolution has itself evolved over the past century and a half. Erik Trinkaus and Pat Shipman’s The Neanderthals: Changing the Image of Mankind from 1992 provides a solid overview of that history, beginning with rivalries between French scientists like Georges Cuvier and Jean-Baptiste-Pierre-Antoine de Monet, Chevalier de Lamarck. (Your automatic response is likely to take the side of a regular-sounding guy named Georges over someone with four hyphenated first names and two de‘s, but you would be on the wrong side of scientific history.) Trinkaus and Shipman fail to arrive at the current scientific consensus that Chris Stringer and Clive Gamble elucidate in In Search of the Neanderthals just a year later, while somehow missing entirely the decades-long rivalry between François Bordes and Lewis Binford. Nevetheless, The Neanderthals is still the most comprehensive history of the subject I’ve read, superseded recently by Dimitra Papagianni and Michael A. Morse’s excellent (but much briefer) The Neanderthals Rediscovered: How Modern Science is Rewriting Their Story (2015).

Armed with a vaguely monomaniacal overview of the chronology of discoveries in paleoanthropology from Engis (the first, then-unrecognized Neanderthal skull) to Rising Star (Homo naledi), I’ll reiterate my assertion above that the last few weeks have seen a series of major discoveries at a previously unprecedented pace.

In May, Lee Berger and his team at Rising Star in South Africa finally announced direct dates for their Homo naledi fossils, placing them between 335,000 and 236,000 years ago, just short of the 195,000-year age for the oldest-known Homo sapiens fossils from Omo Kibish in Ethiopia. This raises the likelihood that small-brained H. naledi and our big-brained Homo sapiens could have co-existed as part of a diverse range of related hominin species in Africa during the Middle Stone Age.

Photo of Homo naledi reconstruction and skeleton (links to National Geographic video)

(I can also heartily recommend Berger’s up-to-the-minute new book Almost Human: The Astonishing Tale of Homo naledi and the Discovery That Changed Our Human Story published alongside the journal article in May.)

Less than a month later, a team including Jean-Jacques Hublin upped the ante with new dates based on thermoluminescence tests of fire-heated stone tools associated with the Jebel Irhoud Homo sapiens fossils excavated in the 1960s. Dates ranging between 315,000 and 286,000 years ago place anatomically modern humans more than 5,200 km across the continent from Omo Kibish, a hundred thousand years earlier. These new dates fundamentally change our understanding of when, and potentially where, anatomically modern humans may have evolved within Africa. Much debate remains, of course, on anatomical modernity vs. behavioral modernity, but the new dates have fascinating implications.

Homo sapiens jaw from Jebel Irhoud
Homo sapiens jaw from Jebel Irhoud (photo credit: Jean-Jacques Hublin)

Africa may be the cradle of both our genus and species, but discoveries that shed light on our species’ evolution and dispersal aren’t limited to Africa itself. Last week, Chris Clarkson and his team at the Madjedbebe rock shelter in northern Australia presented dates of 65,000 years or more (with even deeper layers containing artifacts potentially as old as 80,000 years) for tools used by early Aboriginal inhabitants.

Meanwhile, Aboriginal rock art in Kimberley, Western Australia has been dated to over 60,000 years ago, predating the great Aurignacian art of Chauvet by thousands of years. Both these dates challenge the generally accepted exodus from Africa a mere 50,000 years ago — the first Australians may have needed boats to get from Sundaland (the Malay peninsula, Sumatra, Borneo, and Java) to Sahul (New Guinea and Australia), but they certainly didn’t have airplanes to travel from Africa straight to Australia quite so quickly. (The picture of random individuals floated across 90 km distances accidentally clinging to palm tree logs is frankly just racist…)

Finally, for the moment, research on a new mitochondrial DNA sequence (only the eighteenth Neanderthal individual sequenced so far) place the date for Neanderthal-Homo sapiens interbreeding far deeper in time, as early as 270,000 years ago. Like the new dates for the Jebel Irhoud fossils announced in June, it pushes back the timeline for the very existence of Homo sapiens as a species, as well as our potential dispersal from Africa and interaction with Eurasian Neanderthal populations.

From “Deeply divergent archaic mitochondrial genome provides lower time boundary for African gene flow into Neanderthals” (Posth, et al 2017)

Now, I’m no Clive Gamble, one of the greatest minds working in paleoanthropology today. In Settling the Earth: The Archaeology of Deep Human History, Gamble takes all of the data then available (2013), from nearly two centuries of archaeology and paleontology across the world, throws it in a blender, and presents a work of academic molecular gastronomy. Gamble is nothing if not an iconoclast — one of the first traditional concepts he dispatches is the very concept of prehistory. As the title of the book itself articulates, there is deep human history beneath the shallow, post-Neolithic veneer of the past five to ten thousand years through which we see the world of even older pre-sapiens hominins.

Gamble also takes a global view to the question of how hominins and humans dispersed across the world, eliminating regional and continental boundaries to create five “Terrae” that defined the limits of hominin expansion at various stages over the last 2 million years, from the first emergence of the Homo genus in Africa to our first steps away from our home planet today. For example, lower sea levels during multiple cooler periods (not just the last Ice Age that ended 12,000 years ago) exposed huge expanses of land that enabled dispersal — Sunda in modern Southeast Asia, Doggerland in the North Sea, and of course Beringia familiar to American school children as the “land bridge” between Siberia and Alaska. These were not simply “land bridges” to get between modern geopolitical entities, but expansive, ecologically rich biomes in their own right. Gambles ideas challenged my preconceived notions about population dispersal as well as the intellectual and cultural capabilities of our ancestors, both archaic and modern.

Even without Gamble’s genius, it’s tempting to formulate hypotheses and what-if scenarios that synthesize the discoveries of the last few weeks. If humans were in Australia by 65,000 years ago, the first broadly successful dispersal could not have happened as late as 60,000 years ago. Might the “unsuccessful” population of modern humans excavated in the caves at Qafzeh and Skhul in Isreal who left Africa as much as 120,000 years ago and allegedly died out by 80,000 years ago (replaced by a Neanderthal population from the north, only to be joined by more modern humans from Africa again later) have been partially successful after all? Since modern humans were perfectly capable of building boats to colonize Australia, might the humans of Jebel Irhoud have also built boats to cross to Gibralter, thus providing the basis for the interbreeding evidenced by the German Neanderthal woman from 270,000 years ago? I’ll await the next Grand Theory of Paleoanthropology from the likes of Clive Gamble, Chris Stringer, Ian Tattersall, or Robin Dunbar.

This much we do know: We are a much older species than we thought we were a month ago, by as much as a hundred thousand years. We also ranged farther, earlier than we thought we had barely a week ago — farther across Africa, much earlier to Australia, and maybe even into Neanderthal Europe (at least with people carrying our genes).

What discoveries remain to be shared with the world throughout the rest of 2017 — or even just the rest of this summer?

I’ve linked above mostly to primary sources in journals, but as a lay reader I’m indebted to the excellent science reporting in the Guardian as my starting point. “Via” links follow:

Acheulean tools geologically dated to 1.76 million years ago

A study being published later this week in Nature reports that geologists have dated the Kenyan sediments where a collection of Acheulean tools were discovered, such as the hand ax below, to 1.76 million years ago — at least 160,000 years older than previous dates for technology created by Homo erectus.

Acheulean hand ax

Although the New York Times article summarizing the study focuses on the newsworthiness of these tools as the oldest, it makes a few other interesting points.

The story of human progress is unavoidably a story of technological innovation, Paleolithic designs fading into oblivion as Neolithic tools take their place. Right? Not necessarily.

In reality, it’s not always as simplistic as one technology giving way to the “next,” as these recently dated discoveries show. Older Oldowan tools were discovered alongside the more advanced Acheulean tools, indicating that “the two technologies are not mutually exclusive.”

Other highlights (or, things Andrew didn’t know):

  • The first humans to leave Africa didn’t take the Acheulean technology with them.
  • Acheulean technology wasn’t widely adopted for another several hundred thousand years.

Full article via Boing Boing.

Michael Shermer on shaken souls

“What can be more soul shaking than peering through a 100-inch telescope at a distant galaxy, holding a 100-million-year-old fossil or a 500,000-year-old stone tool in one’s hand, standing before the immense chasm of space and time that is the Grand Canyon, or listening to a scientist who gazed upon the face of the universe’s creation and did not blink? That is deep and sacred science.”

– Michael Shermer, quoted on page 345 of The God Delusion

Proetid trilobite

A Proetid trilobite, a member of one of the last surviving families of trilobites, living until the mass extinction at the end of the Permian about 250 million years ago

The Humans Who Went Extinct by Clive Finlayson

This past year, my reading has alternated between classic science fiction and non-fiction archaeology or anthropology — two very different literary forms that encapsulate opposite ends of our shared and potential experience. Along the way, I’ve discovered three books that truly span the breadth of human history, from past, present, to future. No three books alone could represent millions of years completely, of course, but these books do provide a concise overview, and though written by three different authors, they complement each other to form an overarching story of human existence.

I’ll be posting separate discussions of each book, with a wrap-up of the three after I’m done with them individually. Let’s begin with The Humans Who Went Extinct: Why Neanderthals Died Out and We Survived by evolutionary ecologist Clive Finlayson.

In The Humans Who Went Extinct, Finlayson supplements his direct experience excavating the last stronghold of the Neanderthals at Gorham’s Cave in Gibraltar with multi-disciplinary research for the causes of human extinction. But humans aren’t extinct, right? Wrong.

Some of our close human cousins didn’t quite make it. Homo erectus flourished in Asia for hundreds of thousands of years while Homo neanderthalensis did the same in Europe, long before our own ancestors ever stepped foot outside Africa. Both species made tools similar to our direct ancestors, and DNA evidence indicates that Neanderthals were most likely capable of speech. The received wisdom of contemporary paleoanthropology and archaeology takes the stance that anatomically and behaviorally modern humans (Finlayson conveniently shortens this to the straightforward “Ancestors”) displaced our cousins when we left Africa and spread throughout the Eurasian continent.

Finlayson examines both the material culture of the Neanderthals and the ecological conditions across the past 125,000 years to argue that their environment degraded repeatedly — from dense forests that supported the ambush hunting style of the Neanderthals (as evidenced by their weapons) to steppe-savanna landscapes where herds or individual prey animals were few and far between and which required a fundamentally different set of technologies and behaviors to succeed.

Neanderthals were not able to adapt to the challenges and opportunities presented by the new, more open landscape. (And with one rare but crucial exception in Central Asia, neither were Ancestors.) The range of humans expanded and contracted with the ebb and flow of forests for thousands of years, placing populations under pressure to the point of local extinctions. Finlayson argues that Neanderthals (and Homo erectus) were pushed to the brink of extinction by the contraction of their traditional environments until the small pockets of survivors were no longer viable populations, cut off from each other and susceptible to one bad winter or outbreak of disease. The last Homo erectus lived on Java until as recently as 50,000 years ago, while Homo neanderthalensis held out at Gibraltar until 24,000 years ago.

Meanwhile, Finlayson suggests that Ancestors on the fringes of our traditional comfort zones were being forced to adapt or die. Most died. He traces the origin of the Gravettian culture to an adaptation by a founder population in Central Asia before about 30,000 years ago. The specific adaptations that enabled these people to survive were the centralized villages that served as home base — and most importantly information exchanges and surplus stockpiles — for the hunters, along with new technologies such as lighter, more portable stone tools that could be adapted to new projectile weapons necessary on the open plains. These people spread west to Europe and northeast across the Bering land bridge to the Americas.

Throughout The Humans Who Went Extinct, Finlayson illustrates how the tension between innovation by fringe populations and conservatism among otherwise stable core populations leads to only two possible results when their environments change. In most cases, environmental challenges have been too great and the vast majority of human diversity has not survived. But when the right opportunities happen to be present, the innovators who take advantage of challenges presented by their environment survive while conservatives who fail to do so die.

The impact of ecology on human success or failure is a theme that will appear again in the next two books we examine.

Charles Darwin on grandeur

“Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” – final paragraph of The Origin Of Species

Swans in St. Stephen's Green

These swans in St. Stephen’s Green are of course just one form “most beautiful and most wonderful” descended from dinosaurs.