What a Small Brain Can Tell Us

New information about an early human skull sheds more light on the very first members of the human genus.  The skull, found in Dmanisi, Georgia in 2005, has now been freed from the stone casing that has preserved it for the past 1.8 million years. An international team led by David Lordkipanidze of the Georgian National Museum report its findings in the October 18 issue of the journal Science. 

Photo Caption: The Dmanisi D4500 early Homo cranium in situ. Photo courtesy of Georgian National Museum.

When the world first learned of early human remains in Georgia, the news came as a bit of a shock.  These early humans seemed quite similar to other remains found in Africa and dating to the same time.  That suggests they were able to travel and adapt to new settings. 

The latest analysis contains a new surprise.  The skull described in the new report has an unexpectedly small brain size, at or below the range usually seen as minimal for our genus.  At 546 cubic centimeters, its small brain widens our view of variability of humans at this time. 

Does this skull, identified as Skull 5 from Dmanisi, really measure up to being in the genus Homo at all? It is something else, like Australopithecus?  The researchers argue that it is clearly part of the genus Homo for the simple reason that Skull 5 is found with other, larger-brained skulls, all clearly part of the same community.  One Georgian brain was as large as 730 cc.  What this suggests is that Skull 5 is part of Homo but that our definition of Homo should be broadened. 

In fact, all this diversity at one site provides support for one side in an ongoing debate.  Are species defined broadly in terms of variability, or does small to moderate variation indicate separate species.  This finding supports the view that at least in terms of early humans, a species can be quite variable.      

Not too long ago, Lordkipanidze and his team took the opposite view.  They believed that these early humans from Georgia were a distinct species, what they called Homo georgicus.  The new paper retracts that claim, saying that the new evidence of variation in Georgia means that these fossils fit within the widened range variability of Homo erectus, a globally dispersed species.  More precisely, they see the Georgian samples as best classified as Homo erectus ergaster georgicus, part of the species Homo erectus but distinct because of modifications over time and because of location. 

Commenting on the variation in the skulls found almost literally on top of each other at Dmanisi, co-author Christoph Zollikofer notes that the skulls “look quite different from one another, so it's tempting to publish them as different species.  Yet we know that these individuals came from the same location and the same geological time, so they could, in principle, represent a single population of a single species,” Zollikofer said in a press release issued by the journal Science. 

The key claim advanced in the article, however, is that these samples from Georgia and Africa, together with other samples from Asia, are all part of one global species.  The report describes them as Homo erectus, seen as “a single but polymorphic lineage.” 

The diversity found in Georgia also suggests that the number of individuals in that region may have been larger than first thought, possibly numbering 10,000 or so.  And the small size of Skull 5’s brain suggests that they traveled all this way before brains began to expand.

The report, “A Complete Skull from Dmanisi, Georgia, and the Evolutionary Biology of Early Homo," is published in the 18 October 2013 issue of the journal Science, published by the American Association for the Advancement of Science.    

Did Neandertals Wear Ornaments?

A small but tantalizing find provides further evidence for Neandertal culture.  Working in the foothills of the Alps just north of Venice, Italy, researchers have discovered and analyzed a small marine shell that originally came from about 60 miles away.  It was thinly coated with a dark red substance that turns out to be pure hematite and was most likely used as a pigment.  One possibility is that the shell was used as an ornament.

The paper, freely available online in the journal PLoS One, dates the shell’s pigmentation to a period just before 45,000 years ago, right before the arrival of so-called “modern” humans in Europe. 

Photo Caption: A shell possibly "painted" by Neandertals about 45,000 years ago.  Photo available from PLoS One.

According to the paper, “deliberate transport and coloring of an exotic object, and perhaps its use as pendant, was a component of Neandertal symbolic culture, well before the earliest appearance of the anatomically modern humans in Europe.”

Quoting more of the paper, “this discovery adds to the ever-increasing evidence that Neandertals had symbolic items as part of their culture.”

Debates about Neandertal culture have intensified recently, in part because of genetic evidence of interbreeding between Neandertals and the modern humans coming into Asia and Europe.  While these modern humans began their migration out of Africa about 80,000 years ago and probably interbred around 55,000 years ago, they did not reach Europe until more like 40,000 years ago.  If all these dates hold up in future research, this shell does provide a small but intriguing hint about the culture of Neandertals at just about the time of their encounter with “modern” humans. 

So who exactly is modern?  The differences between ourselves (the humans we like to call “modern”) and the Neandertals are not as great than we once imagined.  The paper ends with these words: “Future discoveries will only add to our appreciation of Neandertals shared capacities with us.”

The paper, entitled "An Ochered Fossil Marine Shell From the Mousterian of FumaneCave, Italy," appears in the current issue of PLoS One and is freely available online.

We Are What We Ate: Diet and Human Evolution

At a key moment in human evolution, our diet expanded and became more diverse, setting the stage for humans to draw on a wider range of food sources to feed expanding brains.

Four academic papers published together in the June 3, 2013 issue of the Proceedings of the National Academy of Sciences report on new methods of studying the carbon found in ancient teeth, going back more than 4 million years.  Ancestors living then ate pretty much what apes eat today, a diet of mostly leaves and fruits.  Then about 3.5 million years ago, a major shift occurs. 
Caption:This is an artist's representation of Paranthropus in southern Africa more than 1 million years ago.  Credit:Illustration courtesy ArchaeologyInfo.com/ScottBjelland.  Usage Restrictions: None

  

The old food sources remained in use, but new sources are added.  Researchers came to this conclusion by analyzing the carbon isotopes still present in ancient teeth.  After examining 175 specimens from 11 different species, they concluded that a key shift occurred at about 3.5 million years ago.  At that point, at least some of our ancestors were supplementing the usual foods by turning to grasses or sedges—or to the animals that graze on them.  These ancestors, including Australopithecus afarensis (best known as the famous “Lucy”), became more diverse in their food sources.

The earliest known evidence suggests that at about this same time, our human ancestors were making tools and using them to butcher large animals for food.  If these animals ate grasses, the carbon would have entered the human diet that way.  Another possibility is that human ancestors were simply learning to identify other types of plants as food sources compatible with human metabolism.

The main point, however, is that at this critical 3.5 million year transition, human ancestors were become more variable in their diet and in their behavior.  Rather than being locked into one type of food source or one way to pursue food, they were becoming more varied in their diet and behavior.  This made it possible for them to exploit more sources of food, nourish even bigger brains, travel and thrive in new niches, and survive climate change cycles, particularly ancient African cycles of wet and dry periods. 

"We don't know exactly what happened," said Matt Sponheimer of Colorado University and one of the researchers. "But we do know that after about 3.5 million years ago, some of these hominids started to eat things that they did not eat before, and it is quite possible that these changes in diet were an important step in becoming human."

If becoming more varied and adaptable is the same as becoming more human, then this study provides an important insight into this process.  One of the papers (Wynn et al.) concludes with this sentence: “This dietary flexibility implies unique landscape use patterns and malleable foraging behavior within a narrow time from of a single species.”  In other words, they were able to adjust quickly, seizing new opportunities and adapting to environmental changes. 



 

The Two Million Year Question

Careful studies of 2-million year old human-like fossils just published in the April 12, 2012 issue of Science raise more questions than they answer.

These papers provide highly detailed information about the teeth, rib cage, hands, and feet of this strange relative, known to scientists as Australopithecus sediba.  But we still do not know the answer to the biggest question of all.  How does sediba fit in the human family tree?  Is sediba a direct human ancestor?  If not, why are they so similar to us in some respects?

Photo Credit: The reconstructed skull and mandible of Australopithecus sediba.Reconstruction by Peter Schmid, Photo by Lee R. Berger. Image courtesy of Lee R. Berger and the University of the Witwatersrand.

The teeth are mostly like those of Australopithecus africanus but also quite a bit like the earliest examples of the genus Homo.  That is surprising.  For some experts, it calls into question the standard view that Homo evolved from Australopithecus afarensis, most commonly known as “Lucy.” 

The new analysis suggests an evolutionary pathway from africanus to sediba to Homo.  In that case, Lucy is a relative but not an ancestor.  Sediba is. 

Not so fast, others insist.  The first examples of Homo may go back to 2.3 million years ago, long before sediba appears at just under two million years ago.  Lucy and her afarensis kin lived much earlier, enough to be ancestral to Homo. 

Based on what we know now, the debate will continue because the facts just do not line up neatly or offer a simple story.  "Our study provides further evidence that sediba is indeed a very close relative of early humans, but we can't definitively determine its position relative to africanus,” study co-author Debbie Guatelli-Steinberg said according to a release from Ohio State University.

What these studies do provide is a remarkably complete picture of what early human-like ancestors look like.  They also provide another surprise.  Despite having a foot with a narrow heel, similar to chimpanzees, sediba definitely walked upright, maybe even using a somewhat awkward never known before to scientists.  They were clearly not knuckle-walkers, like the apes, but they were not nearly as graceful as the humans who followed.  It seems they walked upright differently.  

For now, what all this suggests is that the story of our deep ancestry is more complex than we usually imagine.  Straight ancestral lines are hard to draw.  More finds may help sort things out.  But they may also add new complexity.  The way it looks, multiple forms of early human life may have existed at once.  They differed slightly from each other and also in the degree to which they resemble us.  That makes it very hard to sort out the lineages.  

Is sediba a direct human ancestors?  Yes, at least according Lee Berger, who discovered sediba in a pit in northern South Africa in 2008.  Most experts, however, argue no, mainly the dates are out of line.  What difference does it make?  Perhaps the biggest significance of this debate is to show us that the more we know, the more we see a complex picture of multiple species and perhaps interweaving lineages, making it all the more remarkable that we are here at all. 

This research is published as a set of six research reports in the April 12, 2012 issue of the journal Science, a publication of the American Association for the Advancement of Science. 

Human-Neandertal Interbreeding: When and Where?

Comparison between Neandertal and anatomically modern human genomes shows a history of interbreeding. Some living human beings—those with ancestry in Europe and Asia—carry the results of that interbreeding in their DNA. Those with ancestry in sub-Saharan Africa typically do not.

We also know that Neandertals lived in Eurasia from 230,000 until about 30,000 years ago. Where they came from or why they disappeared remains an open question. And we know that anatomically modern humans first appear in Africa at least 200,000 years ago. Some of them made their way to Asia and Europe sometime in the last 100,000 years.

So when did modern human/Neandertal interbreeding last occur? Did it occur deep in our past, before modern humans and Neandertal ancestors left Africa? Or did it occur after both left Africa, sometime—in other words—within the past 100,000 years?

A new study claims to find evidence that the interbreeding occurred out of Africa. Researchers argue that on the basis careful analysis of the shared DNA, the most recent interbreeding occurred sometime between 37,000 and 86,000 years ago.

Caption: Reconstruction of a Neandertal, 2006, by Stefan Scheer, from Stefanie Krull, Neanderthal Museum Picture Library, Mettmann, Germany

If so, it is pretty strong evidence that the interbreeding occurred after anatomically modern human left Africa. This may have occurred in the Middle East, researchers point out, but probably not just at the beginning of the modern human migration out of Africa. The most recent interbreeding, they conclude, occurs well after this 100,000 date, suggesting ”a more recent period, possibly when modern humans carrying Upper Paleolithic technologies expanded out of Africa.”

In that case, the conceptual challenge posed by the modern human/Neandertal interbreedng remains clearly in front of us. What is the human species? Were Neandertals human? And what are we to make of our new insight into modern human diversity. All puzzling questions, to put it mildly.

The article, "The Date of Interbreeding between Neandertals and Modern Humans," is published in the current issue of PLOS Genetics, where it is available free to the public.

Neandertal Medicine

Neandertals not only ate their vegetables. They used specific plants—even ones that tasted bitter—to treat their ailments. That’s the latest finding from the international team of researchers studying Neandertal remains at in El Sidrón archeological site in northern Spain. Discovered in 1994, El Sidrón has yielded thousands of samples from at least 13 Neandertal individuals.

Using newer techniques of microanalysis, the team studied the dental plaque recovered from teeth of five individuals dating about 50,000 years ago. Lodged in the plaque were tiny microfossil remains of various plants, providing evidence that Neandertals supplemented their diet of meat with a wide range of grain, herbs, and vegetables. The study is published this week in Naturwissenschaften (The Science of Nature).

CAPTION: Researchers working in El Sidrón Cave. Credit: CSIC Comunicación.

"The varied use of plants we identified suggests that the Neanderthal occupants of El Sidrón had a sophisticated knowledge of their natural surroundings which included the ability to select and use certain plants for their nutritional value and for self-medication. While meat was clearly important, our research points to an even more complex diet than has previously been supposed," according to Karen Hardy, a leader in the research team, according to a press release from the University of York.

Neandertals disappeared from Europe and Asia somewhere around 30,000 years ago, often sharing regions with modern humans for thousands of years. Only recently has it become clear that they depended heavily on plants as well as meat for their food.

"The evidence indicating this individual was eating bitter-tasting plants such as yarrow and camomile with little nutritional value is surprising. We know that Neanderthals would find these plants bitter, so it is likely these plants must have been selected for reasons other than taste," said Dr Stephen Buckley, a member of the research team.

The clear implication of the study—that Neandertals recognized the medicinal value of certain plants—provides further evidence of the sophistication of Neanderthal culture and technology. The full scope of Neandertal cultural interaction with modern humans remains an open question.

"El Sidrón has allowed us to banish many of the preconceptions we had of Neanderthals. Thanks to previous studies, we know that they looked after the sick, buried their dead and decorated their bodies. Now another dimension has been added relating to their diet and self-medication," according to Antonio Rosas, also on the research team.

CAPTION: Microscopically visible material entrapped in dental calculus samples – filamentous and cocci bacteria. Credit: Karen Hardy/Naturwissenschaften.

The article, "Neanderthal medics? Evidence for food, cooking and medicinal plants entrapped in dental calculus," is published in the current issue of Naturwissenschafen.

How Old Is Art?

Confirmed dates for the world’s oldest art just got older, according to the report of an international research team published in the May 14 issue of the Proceedings of the National Academy of Sciences.

Dating back about 37,000 years, the art consists of engravings made in stone that has since fallen from the ceiling of a cave at Abri Castanet in southwestern France. While not as visually arresting as the more famous cave art found at Chauvet, the Castanet engravings are both older and represent what is very likely an earlier stage in the history of the Aurignacian culture, which spanned 40,000 to about 28,000 years ago. Some of the Chauvet paintings are now confirmed at between 30,000 and 32,000 years ago.

Credit: HTO. A replica of a painting, now in the public domain.

The Castanet engravings are both simpler artistically and were located in the general living area of the cave. The Aurignacian culture that created both the paintings and the engravings is known for is many forms of art. According to New York University anthropology professor Randall White, one of the study's co-authors, the Aurignacians "had relatively complex social identities communicated through personal ornamentation, and they practiced sculpture and graphic arts."

"But unlike the Chauvet paintings and engravings, which are deep underground and away from living areas, the engravings and paintings at Castanet are directly associated with everyday life, given their proximity to tools, fireplaces, bone and antler tool production, and ornament workshops," White said in press release issued by NYU.

With more refined archeological techniques, the story of the rise of human symbolic culture is likely to become more complex and more ancient. While there may well have been bursts of cultural creativity in which symbolic advance occurred rapidly, additional findings may also suggest a more steady rise in the story of human art. The study, entitled “Context and dating of Aurignacian vulvar representations from Abri Castanet, France,” appears in the May 14, 2012 edition of PNAS.

Human Intelligence: Does It Depend on a Genetic Error?

What makes humans different from the great apes? What makes our brains larger and more complex? We know that our DNA is remarkable similar to other mammals. What subtle genetic changes can explain such huge behavioral differences? One surprising possibility is that our brains are bigger and more complex not so much because of new genes but because of gene duplication.

One gene in particular—SRGAP2—plays a role in how brain cells migrate. It is found widely in mammals of all sorts, from mice to humans. In the great apes, the more archaic form of SRGAP2 results in a relatively slow spread of neurons throughout the brain. Twice in the ancient past, however, SRGAP2 was duplicated, first about 3.4 million years ago and then again around 2.4 million years ago. The second duplication occurred right around the time when the genus Homo separated from Australopithecus. It appears that as a result of these duplications, brains in the Homo lineage—including our own as Homo sapiens—are both large and complex in their number of neuronal connections and in their ability to process information.

A key piece of supporting evidence comes from recent discoveries of the role of SRGAP2 in the development of the human neocortex. When the distinctly human SRGAP2 variants are missing, normal human brain development is impaired. This research appears in two papers appearing May 3, 2012 in the journal Cell. According to one of the papers, “It is intriguing that the general timing of the potentially functional copies…corresponds to the emergence of the genus Homo from Australopithecus (2-3 mya). This period of human evolution has been associated with the expansion of the neocortex and the use of stone tools, as well as dramatic changes in behavior and culture.”

Caption: A team led by Scripps Research Institute scientists has found evidence that, as humans evolved, an extra copy of a brain-development gene allowed neurons to migrate farther and develop more connections. Credit: Photo courtesy of The Scripps Research Institute Usage Restrictions: None

The uniquely human duplications work in a surprising ways, especially the second duplication. The original SRGAP2 remains present in humans today, along with the duplicated versions. The second duplication—SRGAP2C—has the effect of interfering with the original SRGAP2. The reason why SRGAP2C interferes with SRGAP2 rather than boosts it is because the duplicated version is incomplete—in other words, an advantageous copying error.

According to one of the studies, once SRGAP2C appeared about 2.4 million years ago, it created a “dominant negative interaction equivalent to a knockdown of the ancestral copy…The incomplete nature of the segmental duplication was, therefore, ideal to establish the new function by virtue of its structure,” acting in a way that was “instantaneous” in terms of evolution.

"This innovation couldn't have happened without that incomplete duplication," according to Evan Eichler, another leader in the research team. "Our data suggest a mechanism where incomplete duplication of this gene created a novel function 'at birth'."

Even though SRGAP2 duplications seem to play a significant role in distinguishing human beings from the apes, other duplications and mutations are very likely to be involved in the story of human evolution. "There are approximately 30 genes that were selectively duplicated in humans," said Franck Polleux, one of the lead researchers involved in the study, in a press release from the journal. "These are some of our most recent genomic innovations."

Rather than standard mutations, "episodic and large duplication events could have allowed for radical – potentially earth-shattering – changes in brain development and brain function," according to Eichler. For these reasons, this is one of the most intriguing areas for research into the origins of human intelligence.

Whether other duplications—including “incomplete duplications or erroneous copies—also explain our complex brains is something that will be discovered in the next few years.

But what is surprising and somewhat sobering, just based on this SRGAP2 discovery, is how our much-vaunted human uniqueness seems to hang on such a fine thread. If the SGGAP2 duplication is even partly responsible for our complex brains, should we think that our intelligence arose because of a copying error or an incomplete duplication? Is the rise of intelligence and consciousness—truly one of the great events in the story of cosmic evolution—really just based in part on a fluke of nature? Religious or not, hardly anyone is likely to think that thinking is sheer accident.

The papers, Charrier et al.: "Inhibition of SRGAP2 function by its human-specific paralogs induces neoteny during spine maturation" and Dennis et al.: "Human-specific evolution of novel SRGAP2 genes by incomplete segmental duplication," appear in the journal Cell.