A Spark or an Ember?

By John J. Shea, Anthropology Department, Stony Brook University

John Shea with some of his stone age technology. Photo: Larry Engel

Filming The Human Spark with Alan Alda led me to question some of the assumptions we make about the evolution of human uniqueness – the metaphorical “spark” in the title of this series.  Most anthropologists assume that the qualities that made humans unique evolved recently and only among members of our species, Homo sapiens.  But what if this assumption is an accident of history?  Might the things we think make us unique actually be characteristics we share with other hominins who are now extinct?  A spark can be the beginning of a fire, but it can also be the last ember of a conflagration.  What if our spark is not the start of something new, but rather the culmination of a long-running evolutionary trend?

In evolution, only differences matter.  The differences between humans and our nearest primate relatives, the chimpanzees, are not subtle.  We differ in locomotion, in how we use tools, in our diets, in how we get along with one another.  In virtually every way anthropologists care to make comparisons, we differ more from chimpanzees than chimpanzees differ from other apes.  Genetic studies suggest these differences accumulated over nearly 6 million years.  If all one had to work with were comparisons of the morphology, genetics and behavior of living species, one could not help but conclude that we are special, that we humans have a “spark” that chimpanzees and other apes do not.

But we know there is a fossil record for human evolution, and it tells a very different story.  Humans evolved in the Pleistocene Epoch (2.5 Million to 12,500 years ago).  This was a momentous period in the evolution of life on Earth.  It was a great time to be a hominin.  The term hominin refers to the group of bipedal primates that includes humans.  Two million years ago there were at least three major groups of hominins, Australopithecus, Paranthropus, and Homo, all living in Africa.  Each of these groups comprised at least two and almost certainly more distinct species.  For much of the Pleistocene, there was more than one human-like species walking the Earth at any one point in time.  As recently as 40,000 years ago, there were at least three, Neandertals in Europe, Homo sapiens in Africa and Asia, and Homo floresiensis in Indonesia.  Today there is only one hominin species, us.

Being the sole remaining contestant of “Survivor: Pleistocene” influences our ideas about our “human spark” and about the nature of human uniqueness.  Our “human spark” looks special to us because we cannot compare it directly to those of our extinct hominin relatives.  The evolutionary gulf between living apes and us is a recent evolutionary condition.  If one takes extinct hominins into account, the gulf between humans and apes will appear not so wide, because it would be populated by countless ape and hominin species.  Each species would have had its own “spark,” its own uniquely evolved characteristics, and those characteristics would differ with evolutionary distance.  Species with a recent common ancestor would be more similar to one another.  Our “human spark” would be very similar to that of the Neandertals, less similar to that of Homo floresiensis, and very different from that of Australopithecus.  Our “human spark” would still differ from those of living apes, but along a complex continuum of ape and hominin variation.

What caused the reduction of species in the Genus Homo?  The simple answer is that we do not know, but we can venture some well-founded hypotheses.  Climate change and habitat loss almost certainly played a role, as they do in recent animal extinctions.  Many early hominin fossils (particularly australopithecus and paranthropus) are found in woodland habitats.  Such woodlands have been losing ground to grasslands for the last two million years.  Predators may have played a role.  The carnivores that preyed on australopithecines and paranthropines were mostly solitary felids (large cats like leopards).  The Pleistocene witnessed the evolution of large social carnivores, like lions and wolves.  These carnivores may have caused problems for some hominin species, either preying on them directly or out-competing them for access to meat and fat from large animal carcasses.  Bad luck may have played a role, as well.  Neandertals lived in some of the coldest habitats ever occupied by primates during a period of rapid, near chaotic climate change.  Their extinction, though tragic, is not particularly surprising.

Paleoanthropologists have been strangely reluctant to consider the role of competition among hominin species in the evolution of the Genus Homo.  Yet, competition is the engine that drives evolution.  In evolutionary competition, your most formidable rivals are those to whom you are most closely related.  Homo sapiens’ evolutionary success must have come at the expense of other hominin species, most likely those closely related to us.  One can see proof of this in a pattern that occurs in the fossil record.  In region after region, the first appearance date of Homo sapiens fossils is closely correlated with the last appearance dates of other hominin species.  There appear to have been some places where other species “held their ground:” Neandertals in southern Spain, Homo floresiensis in the forests of Indonesia, but these are exceptions, and in neither case is there clear and convincing evidence for long-term, face-to-face encounters between our species and other hominins.

This is why I am skeptical about arguments that early Homo sapiens killed off the Neandertals and other hominins.  It is not that I think they were necessarily good-natured.  Their moral sentiments probably varied widely, just as ours do.  Rather, I think they just did not encounter other hominin species often enough for the benefits of sustained conflict to exceed the risks and costs.

So, why did Homo sapiens survive and other hominins become extinct?  One key to our “human spark” is our uniquely broad ecological niche.  An ecological niche is the network of predator-prey relationships between one species and other species.  In evolutionary competition, generalists (species with a complex niche) always beat specialists (species with a simple one).  Homo sapiens is the ultimate generalist.  We sustain ourselves on animal prey ranging from snails to elephants, on birds, fish, and countless plant foods.  Much of this niche breadth reflects recent innovations, such as agriculture and pastoralism.  I am increasingly convinced that there was an earlier “revolution” in our ancestral human niche, one underwritten by the use of projectile weaponry.  Projectile weapons, such as the bow and arrow are niche-broadening tools.  The same bow that can launch an arrow at a fish or rodent can bring down an elephant, when it is tipped with poison.  Projectile weaponry is uniquely human and culturally universal.   We are the only species that uses projectile weaponry, and no human society has ever abandoned its use.

In seeking the origins of human uniqueness, I think it is absolutely crucial for archaeologists to work out when and where humans began using projectile weaponry to broaden their ecological niche.  Right now, evidence in the form of stone points similar to recent arrowheads is strongest in equatorial Africa, the region in which Homo sapiens first evolved.  The strongest such evidence dates to between 50,000 to 100,000 years ago, but as noted in the Human Spark, new discoveries will almost certainly push these dates back further.  I do not think that projectile technology alone explains human uniqueness.  Nothing in evolution is that simple.  Yet, projectile weaponry is an interesting piece of our human evolutionary puzzle that has not received the scientific attention it deserves.

Some academics look down at television programming as “merely” entertainment.  I disagree.  If you take public money for your education (as I did), and expend such funds in your research (as I do), you have a moral obligation share the fruits of your studies as broadly and effectively as possible.  Far more people will view the Human Spark than will ever listen to my academic lectures or read any of my scientific papers.  The most effective way to show how scientific research about human evolution matters is by working with people like Alan and his colleagues to create a thought-provoking program like the Human Spark.

Alan Alda and John Shea work on stone tools side by side. Photo: © Larry Engel 2008

How does your research relate to the idea of a “human spark?”

Describing human uniqueness as a “spark” suggests that what makes us unique as a species is, like fire, something that grows from small beginnings to something larger and more transformative. Most evolutionary changes start small. The risk of taking the spark metaphor too literally in human origins research is that it is exceedingly unlikely that our species’ uniqueness arose from just one small change. Nothing in evolution is that simple. A particular scientist may champion one factor or another as a prime mover in human evolution, but this has more to do with academic politics than it does with a realistic view of how evolution actually works. Programs like The Human Spark are good because they show the wide range of information we paleoanthropologists have to pull together to create testable hypotheses about the course of human evolution.

How did you become interested in paleoanthropology and eventually wind up at Stony Brook University?

When I was young, I read many books about ancient Greek, Roman, and Norse mythology. I was also interested in woodcraft – hiking, fishing, camping, and other “Boy Scout” kinds of things. These interests converged in studying archaeology at Boston University. At Harvard, I became especially interested in finding links between archaeology and physical anthropology.

John Shea shows off some replica spears to Alan Alda in front of the Human Spark film crew. Photo: Maggie Villiger

What you are working on these days?

I am currently researching the origins of projectile weaponry (bows and arrow, spearthrowers, etc.) by making and using replicas of these weapon systems. Projectile weapons are used by all known human societies and used only by Homo sapiens among all living animals. My research suggests projectile weaponry enabled our ancestors to create a broad, flexible, and stable ecological niche that gave them a competitive advantage over other hominin species.

Why is this kind of research important to pursue?

How we humans differ from other animals and from one another is the most important question in anthropology. It is, in essence, the question from which all other anthropological questions originate. If projectile weaponry played a significant role in our species’ origins and global dispersal, then we may have found one part of the answer to the “big question” of anthropology.

What are the wider-ranging implications of your projectile research?

If projectile weaponry is as ancient as my research suggests, then this implies that responsible weapon use is an important part of our evolutionary heritage. It has got our species through some tough times. I think it is important to preserve this ethic of responsibility. I strongly support the right to bear arms, provided the people who do so possess the same responsibility and intelligence about using them as our Ice Age ancestors did.

John and Alan try their hand at hunting with projectile technology – but their prey is a Styrofoam deer. Credit: © Larry Engel 2008

What’s it like actually doing the day-to-day work that leads to all the big ideas and theories?

Few big ideas actually occur when I am surveying, digging or working in the lab. My best ideas typically crop up when it is least convenient to write them down – while lecturing to students in class or while riding my mountain bike through the woods.

What do you think the future of your field might hold?

As we learn more about the earliest phases in the evolution of Homo sapiens, we are either going to find that their behavior was just as complex as ours or that it was organized fundamentally differently from ours. In either case, what we find is going to challenge people’s assumptions about human uniqueness.

What was it like working with the Human Spark film crew?

Television airtime is expensive. You have to make your point quickly and economically. A good producer, like Graham Chedd, helps you learn how to do this. Several times, I dashed back to my office to write down a new idea, or some particularly apt way of phrasing something that occurred to me while filming.

Also check out this interview clip of John Shea talking about The Human Spark and his contributions to the show.

Photo by Aaron Logan

One of the ways The Human Spark investigates what makes us uniquely human is by looking at our closest living relatives, the other great apes. Scientists are attacking the question of how we became human from a number of new directions – in addition to analyzing the more traditional hard evidence of ancient fossils. This article in New Scientist magazine explains several ways researchers are gathering data from primate groups alive today to gain insights into early hominid evolution. Tune in to The Human Spark’s second episode to learn more. What do you think these kinds of inferences can add to our understanding of where we came from and how we became who we are?

• New Scientist: “Ape behavior reveals secrets of human evolution“

by Vicky Horner, Living Links Center, Emory University

To many people, the words “culture” and “chimpanzee” don’t seem to go together. In fact, apart from starting with the same letter, they seem to have little connection at all. It’s therefore always slightly awkward when I have to explain what I do for a living to someone I don’t know very well. When I tell them that I am a psychologist, but that I work with chimpanzees and study their cultural behavior, I get the distinct impression that some folks think perhaps it is me, and not the chimps, that needs a psychologist!

The looks of surprise and confusion come from the fact that for many people the notion of culture equates with the fine arts, a night at the opera, or a refined palate for expensive wine. The idea of a chimpanzee at the opera sipping on a nice glass of chardonnay is pretty comical, even to me. We can all think of lots of examples of cultural differences between groups of people, but actually defining it in biological terms is a little more difficult. Psychologists, anthropologists and biologists have been arguing about culture for decades, and although we still don’t agree, we are getting a little closer to a definition that keeps most people happy. In order to understand culture, and more importantly to understand the evolution of our own cultural abilities, we need to stop getting caught up in examples of our cultural behavior and focus more on how cultural differences develop in the first place. At the fundamental level, culture is simply a collection of learned behaviors that have been passed on from one generation to the next, such as using chopsticks or knives and forks. For many years culture has been regarded as the hallmark of our species, the ‘human spark’ that separates us from other animals. However, before we can make claims about our own uniqueness, we need to check for similar sparks in other animals, starting with our closest living relatives, the chimpanzees, with whom we share a common ancestor and about 99 percent of our DNA.

One of the Yerkes chimps uses a tool to extract a tasty treat from one of Vicky’s puzzle boxes.

A few years ago, a group of scientists working in Africa got together to compare the behavior of the chimpanzees at their field sites. What they found was rather surprising. At every site, the chimpanzees displayed a totally different pattern of behavior, such as how they use tools and weapons. These differences were not easily explained by differences in habitat or genetics. The scientists therefore thought that perhaps these differences represented chimpanzee cultures, and arose because each group had invented different solutions to similar problems (like dipping for ants with long sticks or short sticks), and that these behaviors were maintained over generations by learning from one another.

However, it is very difficult to study culture and learning in the forest because there are so many variables, so at the Living Links Center we study chimpanzee culture in a more controlled captive environment. We study two social groups of chimpanzees who live in large indoor-outdoor enclosures with climbing structures, grass and toys.  We train one chimpanzee in each group to act as an “inventor” who solves a food puzzle (like how to get the banana out of the box with a stick) in one of two different ways. We then track if and how each new behavior spreads within the groups. These studies are important because they show us that chimpanzees have the brains for culture; they can learn and maintain new behaviors accurately enough to support the reports of culture from the wild. I am not claiming that there is no difference between going out to a Chinese restaurant to practice your chopstick skills and staying home to fish for termites in the back yard, but the fundamental psychological mechanism and the evolutionary driving force behind the two is the same.

Alan tries his hand at a puzzle box, though he’s not quite as motivated as a typical chimp to extract the M&M.

So what does all this mean for the human spark? To me there is no single spark that separates us from chimpanzees; we are intricately connected by our common ancestry. The differences between us arise from thousands of tiny differences in the frequency and contexts in which we do things. For example, we imitate one another constantly; chimpanzees imitate each other sometimes. We take other people’s perspectives on situations frequently; chimpanzees take another’s perspective sometimes. We empathize frequently, they empathize in some contexts. It is all of these little tweaks here and there that make up the human spark.

On a final note, I’d like to emphasize the importance of not falling into the trap of thinking that we are the ultimate and desirable endpoint of evolution. Chimpanzees and humans have both been evolving form our common ancestor for the last 5 million years. They may not be at the opera, but chimpanzee culture is remarkable in comparison to other species. We also have a habit of measuring their abilities against our own human checklist in the quest for the human spark. But what would happen if we measured ourselves on a chimpanzee checklist; would we find a “chimpanzee spark”? How do you measure up to this five-year-old chimpanzee?

Heat treatment transforms the poor quality silcrete on the left into the ideal tool making material on the right. (Photo by Kyle Brown / South African Coast Paleoclimate, Paleoenvironment, Paleoecology, Paleoanthropology Project © Copyright Arizona Board of Regents)

Pyroengineering. A big word for what early modern humans learned to do at least 72,000 years ago, according to researchers.

A team of archaeologists says that ancient humans harnessed the power of fire to transform stone raw material into an improved form for tool making. It’s next to impossible to fashion sharp stone blades from a stone called silcrete as it naturally occurs. But if silcrete is heat treated, it can then be worked into advanced tools.

This complex technology is another example of that behavioral modernity we are calling the Human Spark – and it’s occurring on the southern tip of Africa tens of thousands of years earlier than the Human Spark is evident in Europe.

When the Human Spark team filmed with Arizona State University’s Curtis Marean, he told Alan Alda about his group’s discovery at Pinnacle Point in South Africa. Watch this video to hear how the scientists figured out the secret of the silcrete.

More information:

• ScienceNews: “Fire Engineers of the Stone Age“
• New Scientist: “Earliest Fired Knives Improved Stone Age Tool kit“

Darwinium masillae

Our series attempts to locate when and where we transitioned into truly modern human beings — the elusive spark, if you will, that allowed us, here on our own tiny branch on the tree of life, to behave the way we do with all our various abilities and features. Part of this quest involves closely examining our direct ancient lineage, as well as our near and not-so-near cousins. Of course evolutionary history is filled with groups that split into various descendant lines as well as those that hit dead ends and fizzled out. These ancient family trees are pieced together through the fossil record. Looking at the various branches on these trees is one way scientists try to figure out the relationships between various animal ancestors and us.

Recent publications about a fossil called Ida provide the latest example of a creature that seems to have lived at one of those branching points where one group of animals was evolving into a recognizably different one. People in the media have jumped all over this beautifully preserved 47-million-year-old fossil, with some even calling it a “missing link.” Of course, there’s never a single missing link in the huge web of animal evolution, but it does appear that Ida, or Darwinium masillae, was a mammal who shared characteristics with the prosimians (such as lemurs) and also with anthropoids (such as monkeys and apes). Keep in mind, there’s a long, long time — and lots of evolution! — between when Ida lived and when our own species appeared on earth maybe 200,000 years ago.

What do you think of all the media hoopla about Ida and what she means?

• Research article: “Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology“
• Associated Press: “Early Skeleton Sheds Light on Primate Evolution“
• CNN: “Scientists Piece Together Human Ancestry“
• The Independent (UK): “The Big Question: Is ‘Ida’ really the missing link between humans and animals?“

Watch Hauser explain to Alan Alda his concept of humaniqueness – and how we can draw on a multitude of talents to solve a problem, whereas other species are limited to just a few.

When Amanda Henry went through airport security in Washington on her way to Boston she made the inspector nervous when her bag revealed dental instruments – apparently the security officer hates going to the dentist. The officer may have been even more freaked out if she knew the teeth Amanda was on her way to clean with her dental picks belonged to a 100,000-year-old.

A very famous 100,000-year-old at that – at least in archeological circles. The teeth are still all neatly in place in a skull now at the Peabody Museum of Harvard University [tons of images here], where it has resided in secure climate-controlled storage since it was unearthed in the 1930s from a cave in Mount Carmel, in present-day Israel. We had met the skull the day before, when Dan Lieberman had arranged for it to be brought out of storage and introduced to Alan.

Known as Skhul 5, the skull is the oldest known human with almost modern features, and so plays a pivotal role in our story. He poses the central puzzle we’re trying to get to the bottom of: people looked like us apparently long before they started behaving like us – at least according to the commonly accepted view that the modern human mind – with what we are calling the Human Spark – didn’t evolve until tens of thousands of years after the owner of the Skhul skull and his like lived in the Middle East – most likely alongside, or at least at the same time as, their cousins the Neanderthals.

The Human Spark camera rolls while Amanda demonstrates her dental scraping techniques to Alan. Photo: Maggie Villiger

As we’d just been learning from Alison Brooks, it’s now looking increasingly likely that the Human Spark in fact started to glimmer much earlier in Africa, perhaps even before the ancestors of Skhul 5 made their way north. So archeologists would love to know as much as possible about how Skhul 5 lived. It was Alison who told us about Amanda, a student of hers at George Washington University, who – armed with her dental picks – was going to demonstrate to Alan how she’s figuring out what Skhul 5 ate.

After carefully removing the skull from its padded box, Amanda showed us how she very, very gently scrapes dental plaque from the skull’s molars (much more gently than your oral hygienist cleans yours).  Plaque, she explained, is the perfect material to preserve microfossils from the plants Skhul 5 ate – starch grains and tiny silica bodies called phytoliths that Amanda will be able to identify under the microscope and tell what plants they came from.

Amanda’s care in her scraping wasn’t only because, as she reminded us, the skull is priceless, but also because, “I have to leave some plaque behind in case somebody comes up with a different way for studying it in the future.”

Alan wanted to know if she poked around in his teeth, could she find out what he’s eaten.

Amanda: Well it depends, how good are you at brushing and flossing?

Alan: Oh just great, yes.

Amanda: I’ve actually done some experiments where you eat whatever you normally eat for breakfast, lunch and dinner. At the end of the day , you take one of these dental picks…

Alan: And you could say what the person had eaten?

Amanda: Some of it, sure.

Alan: No kidding.

Amanda: It’s quite easy. It’s not just in the plaque. It’s in any of the pellical, basically the scum that builds up on your teeth. As that hardens into plaque then it’s more permanently kept on your teeth. I don’t know, actually, how far back I’d be able to tell what you ate, whether I could just tell this morning what you had for breakfast, or what you had three weeks ago.

Fortunately for Amanda, and despite the astonishingly good shape of Skhul 5’s teeth, he lived a good long time before the invention of dental floss, so she has high hopes of discovering what he ate 100,000 years ago.

Alan summed up the reaction of all of us: “Astonishing.”

- Graham Chedd