The Streetlight Effect and Historical Amnesia

Our understanding of the past is distorted by various factors

Patrick Wyman over at Perspectives has an interesting article talking about the Shigir Idol and how it alters our conception of the deep human past.

We talked about the Shigir Idol in the context of how fission-fusion societies occasionally congregated in large numbers even though they probably spent most of the year in smaller hunting parties. Thus, I pointed out that thinking about prehistory solely in terms of small mobile foraging bands was missing a whole lot of the big picture about how early human societies developed.

The Shigir Idol was obviously far too large to be carried around by mobile hunters. That means either 1.) The people who made it were not mobile, but at least semi-sedentary and spent a good part of the year close to where the idol was located; or 2.) The idol marked out a sacred space that dispersed foraging bands would periodically return to, probably for ritual purposes. Remember, the Idol long predates agriculture at over 12,000 years old.

As Wyman notes, it's only because of very fortunate circumstances that the artifact was preserved at all. But it forces us to confront just how much of prehistory has been lost to us forever, and how that affects—and even distorts—our understanding of the human past:

...much of the past is simply lost to us due to the nature of what tends to stick around. Stone tools, sure; pottery sherds; often, metal objects; sometimes, human remains. We practically never find hide or textile clothing, any kind of wooden item, or woven baskets. Human remains quickly decompose; even if carefully buried, acidic soil conditions might eat away even the durable bone. Only rarely does soft tissue, skin, or hair survive.

What preserves in the ground makes up only a tiny fraction of the material world in which people lived, thrived, and died. Because of this, our access to their world will always be extremely limited...

It’s something we must constantly bear in mind when thinking about the past. Our picture is inherently incomplete, our access limited. That doesn’t mean the task of understanding the past is hopeless, but embracing the limits of what we know is essential to doing the job right.

The Perishable Past (Perspectives)

I want to piggyback off of that to make some related points.

There are all sort of things that have caused us to get the remote past very wrong. Some of them we've started to correct. Others are still clouding our view.

There’s a common joke about a man looking for his lost car keys. Here's one version:

A police officer sees a drunken man intently searching the ground near a lamppost and asks him the goal of his quest. The inebriate replies that he is looking for his car keys, and the officer helps for a few minutes without success then he asks whether the man is certain that he dropped the keys near the lamppost.

“No,” is the reply, “I lost the keys somewhere across the street.” “Why look here?” asks the surprised and irritated officer. “The light is much better here,” the intoxicated man responds with aplomb.

This joke gave rise to the term "streetlight effect" to describe this phenomenon. It turns out that the streetlight effect observational bias has exerted a powerful, ongoing influence on the way we think about prehistory, and sometimes even more recent history.

For example, many of the earliest fossils of human origins were found in the Great Rift Valley in Africa. It was subsequently assumed that this region must have been the crucible of early man—the place where Homo sapiens had evolved. The famous "Lucy" fossil was discovered here. The earliest stone tools were discovered here. The Omo and Herto skulls, which were for a long time the earliest anatomically modern human skulls found anywhere in the world, were also found here. This led to the Great Rift Valley being pinpointed as the definitive cradle of human evolution. It was here, the thinking went, where modern humans must have arisen in Africa.

As this became the widely accepted view during the 1960s and 1970s, further searches for early human fossils concentrated on this area, assuring that more fossils would be discovered here, thus further reinforcing the conventional wisdom.

But it turns out that the conditions in the Great Rift Valley just happen to some of the best anywhere in Africa for preserving early human remains. Did this distort our understanding of where early humans evolved? Almost certainly yes. Did it distort our understanding of which fossils were our remote ancestors? Again, almost certainly yes. We were looking where the light was, not where the keys were.

Subsequent discoveries have shown that the coast of South Africa is just as likely to have been the place where early humans first emerged. Some of the earliest signs of a cognitive leap have been found in caves located here. The 260,000 year-old Florisbad skull was also found in South Africa. The oldest necklaces made from snail shells have been found in Israel and Algeria. And the earliest anatomically modern human skulls currently come from Jebel Irhoud in Morocco dating a couple hundred thousand years earlier than the Omo and Herto skulls from Ethiopia.

This had led scholars to increasingly conclude that there was no crucible for early man, and that human evolution was a pan-African phenomenon. According to the new view, all sort of unique adaptations arose in isolated populations all across the continent, and these populations repeatedly mixed and separated over millions of years due to oscillating climate conditions causing them to exchanging genes and—quite possibly—cultural adaptations as well.

But that's just the beginning.

In my posts on the Plant Trap, I noted that animal bones tend to be preserved in prehistoric sites whereas plant material rapidly decays into compost. This has caused us to overemphasize the importance of hunting in early human cultures and overlook the importance of gathering plant foods. With improved techniques such as phytolith analysis and floating techniques, this is starting to change. These techniques told us, for example, that there was intensive cultivation of plant foods in the Amazon basin as far back as 8,000 years ago, and maybe even earlier.

Understanding this fact makes the transition to horticulture at the onset of the Holocene—and subsequently to agriculture—a lot easier to understand. Although see this:

What did our ancestors eat during the stone age? Mostly meat (Science Daily). Based on this study, the effect of the extinction of large prey animals—especially Proboscideans—on the subsequent trajectory of human history cannot be overestimated.

Another important fact distorting our understanding of the past is that a lot of areas which used to be dry land are now under water. This image demonstrates clearly that even today (except for population-dense Asia) humans are a coastal species.

Coasts are to some degree the natural habitat of Homo sapiens, meaning that those are the places where our earliest ancestors probably congregated when they left Africa, and so that's where the best evidence about who they were and how they lived would be located.

It now looks like the earliest migrations out of Africa were coastal routes eastward along the shores of southern Asia towards Australia. Only later did we migrate overland to the Near East and into Eurasia. And it's also increasingly looking like the Americas were first populated via a coastal route, with inland migrations coming later only after the glaciers started receding.

This makes sense. Coastal ares provided a ready source of food in the form of fish and shellfish, as well as water (sources of fresh water are often found close to the shore) and salt (which is a necessary nutrient). The sea route into the Americas has been described as a kelp highway. After all, who wouldn't want to live on a beach? Coastal property is still the most valuable property in the world today.

The problem is that after the end of the last Ice Age 18,000 years ago, rising sea levels inundated coastal areas all over the world. Sometimes these areas were fairly small, but sometimes they were huge. Asia and the Americas were connected. The British Isles were part of the European mainland. The large islands of Indonesia were connected to mainland southeast Asia. Australia, New Guinea and Tasmania formed one single continent. The Persian Gulf and the Baltic Sea were dry land and the Black Sea was a fraction of its current size. One scientist put it this way: "During the Last Glacial Maximum, the ocean surface was 410 feet lower than today. So, worldwide the amount of land that has been lost since the glaciers melted is equivalent to South America."

Remnants of human migration paths exist underwater at 'choke points' (Science Daily)

Think about that—an area the size of South America, lost to archaeology forever!

That means that the sites we've discovered inland are actually the outliers, not the typical human settlements back then. That fact is not given anywhere near the attention it deserves. Perhaps the reason people once thought that a "cognitive leap" happened only 40,000 years ago was because all the older evidence has been lost under the waters. Inland areas were probably only colonized once the coastal areas became overcrowded—which is to say, much later on. It appears that the preferred option for early man was to go find beachfront property somewhere else in the world rather than move inland. It's hard to explain the emerging pattern of human expansion and settlement otherwise.

This probably gives us a distorted view of what many societies looked like back then. Anthropologists have long assumed that nomadic band-level societies found in southern Africa were representative of the majority of human societies before agriculture came along 10,000 years ago. But were they?

We now know that sedentary societies were possible in the absence of any sort of large-scale cultivation. Some of these societies were fairly large and complex. Were these societies more common thousands of years ago, and band societies the exception? After all, band societies may be an adaptation to being pushed into the most marginal regions of the globe by food-producers rather than a "default" mode of social organization. Many of the most productive regions of the world were the first to take up cultivation, even taking into account how many early societies must now be under water.

The anthropologist Manvir Singh recently published a paper where he argued exactly that. He contends that early human cultures were probably much more diverse in terms of specialization, hierarchy, settlement patterns, and so forth than what we find in small-scale band societies like the !Kung. He summarized his paper in an article for Aeon Magazine:

...the more we dig through history, the more we encounter foragers who were sedentary and hierarchical. They covered Japan before agriculture. They dotted the South China coast before agriculture. They inhabited the Levant, tracts of the Nile, the beaches of southern Scandinavia, the central plains of Russia, the coasts of the Atacama Desert, and the grasslands of the high-altitude Andes—all before agricultural peoples dominated those regions. Even today, sedentary foragers live in riverine and coastal regions of New Guinea.

Sedentary and hierarchical hunter-gatherers are not unusual. If anything, it’s the profusion of mobile, egalitarian bands that might be the historical outlier. Rather than reflecting ancient ways, these small-scale societies are often products of modern forces. Rather than being untouched, many have been bullied, pacified, employed, enslaved and marginalised by colonial powers and agricultural neighbours.

So why haven't we found evidence of such civilizations in Africa prior to the exodus of early man? Singh basically argues that absence of evidence is not evidence of absence, along with the streetlight effect:

...consider the Calusa. Their kingdom existed less than 500 years ago. They ruled an area larger than Switzerland. They were documented by Europeans. Their capital was 10 miles from the modern city of Cape Coral. Yet they were largely unknown to archaeologists until the 1970s.

Now imagine a similar site in Africa, except that it lacks documentation, is older by 100,000 years, and is more remote from centres of archaeological research, plus far fewer people are digging around for it.

Perhaps this makes artifacts like the the Shigir Idol easier to understand. In keeping with the theme of the post, how much of the evidence for this hasn't been preserved or has simply rotted away?

It's important not to read too much into this. No matter how complex these lost civilizations might have been, today's levels of hierarchy, exploitation, and extreme inequality are still unprecedented. But it does mean that early human societies were far more complex and variable than we first assumed. We know that many foraging societies adjusted their social structure based on the demands of the moment, often cycling between more and less egalitarian frameworks over periods of time.

Even when in comes to recorded history, the pride of place the ancient Near East gets relative to other parts of the world has been exaggerated. This is because southern Iraq was intensively investigated by British and French archaeologists at the beginning of the twentieth century who were heavily influenced by the Bible—either explicitly or implicitly. They assumed that civilization must have begun in this area. After all, Mesopotamia was the location of Biblical Garden of Eden, the Tower of Babel, and was the home of the biblical patriarch Abraham. Conveniently for them, these regions were occupied by Europeans during the age of colonialism, making them amenable to archaeological exploration unlike other more remote parts of the world.

So that's were they looked, and sure enough, they found plenty of evidence for early civilizations like cities, temples, and writing. And so, in all the old history books, Mesopotamia was invariably depicted as the place where civilization began, along with ancient Egypt (where the Israelites were held in captivity according to the Bible). Cultural and technological developments were seen as beginning in these places and radiating outward from there to more "primitive" cultures throughout the rest of the region over the course of history like a game of telephone or a viral infection.

But this story, too, is looking less and less likely. What caused this reevaluation was the arrival of more precise dating methods like radio-carbon 14 dating. Using these methods, it turned out that many places which were thought to be influenced by the spread of culture and technology from the ancient Near East actually predated them—in some cases quite significantly!

We now know, for example, that Stonehenge is older than the pyramids—a lot older. There are a number of megalithic sites which predate temples in both Iraq and Egypt, such as the ones on the Mediterranean island of Malta and the burial mound of Newgrange in Ireland. The neolithic Vinča culture of the Balkans appears to have developed coppersmithing without any influence from the Near East. There are even signs that this culture had a form of proto-writing which predates cuneiform based on artifacts like the Tărtăria and Gradeshnitsa tablets. The discovery and excavation of Göbekli Tepe in the 1990s further upended a lot of the conventional thinking about what cultures before agriculture were capable of. More and more similarly ancient sites are still being discovered in this same region of Turkey.

Before Uruk and Ur were established there may have been cities of up to 15,000 people north of the Black Sea evidenced by sites like Talianki which belonged to neolithic Cucuteni–Trypilli culture. Because these settlements were made of natural materials like earth and wood, they didn't preserve nearly as well as stone and mud brick temples did in the dry deserts of Iraq and Egypt. Plus, for reasons unknown to us, it looks like they periodically burned down their cities and rebuilt them over many years, further obscuring their existence. And many people today remain unaware that the oldest mummies ever discovered don't come from Egypt—they come from South America.

These lost civlizations are only now starting to come to light thanks to the dedicated efforts of archaelogists, but it's a slow and often painstaking process. A lot of history books are already out of date and will have to be rewritten in the coming years.

It now looks more like the rise of cultures like ancient Egypt and Mesopotamia and cities like Uruk and Ur were not sudden, isolated phenomena, but part of a broader set of cultural developments which were taking place all over the world at this time. Once again, we were looking where the light was, not where they keys were.

What Bayes' Theorem tell us about history

Another thing to keep in mind when reading about ancient discoveries is Bayes' Theorem.

I like to use this example for Bayesian thinking: if I described to you a guy who was muscular, covered in tattoos, was proficient in boxing and ju-jitsu, and listened to Joe Rogan a lot, would you say that this guy was more likely to be a professional MMA figher or an accountant?

The answer is that he's more likely to be an accountant. Why? because the number of professional MMA fighters is vanishingly small, like under a thousand. By contrast, accountant is one of the most common professions in the United States today.

The point is that hidden odds often cause our initial intuition to be wrong, and that probabilities need to be taken into account when evaluating information based on surface appearances.

What's that got to do with ancient history, you ask? Well, the important point is this:

The first instance of something that we've discovered is in all likelihood not the first instance that actually existed. The odds that we just happened by sheer luck to stumble upon the very first instance of something given the extreme paucity of surviving evidence from prehistory is almost astronomically small. And the farther back you go in time, the more likley this is to be the case!

So if we find, for example, a piece of cloth from 30,000 years ago, it's quite likely that it was not the very first piece of cloth in existence anywhere in world. We can safely infer that the use of cloth probably goes back further. How much further? Well, that's the problem—it's impossible to say. Even if we subsequently found an even earlier instance of something, it's still in all likelihood not the very first one ever produced, unless its something that preserves very well like pottery or we got extremely lucky.

This is important to keep in mind when you hear about the earliest ‘X’ ever discovered. It’s really the earliest ‘X’ that we know about. Its almost certainly not the earliest ‘X’, especially when it comes to prehistory. What his means is that, in many ways, humans were probably a lot more sophisticated a lot earlier than many archaeologists and prehsitorians give us credit for.

This came to mind recently when reading about the Antikythera Mechanism. This artifact was discovered by sponge divers in a shipwreck off the Greek island of Antikythera at the beginning of the twentieth century. Recently, it's been in the news again because a team of scientists have made a number of breakthroughs in understanding how it worked. It's an amazing story. Fortunately for us, the team put together a short film explaining how they did it. It's a half and hour long and free on Vimeo, and I highly recommend watching it:

The Antikythera Cosmos (Vimeo)

Scientists may have solved ancient mystery of 'first computer' (Guardian)

If this "analog computer" was truly the only one of its kind in the entire ancient world—like, literally the only one—the fact that it just happened to go down in a shipwreck where it could be discovered thousands of years later is quite fortunate is it not? What's far more likely is that there were a lot more of these types of things around but they've mostly been lost to us in the mists of time.

It was pure luck that we fished this thing out of the Mediterranean in 1901. (By the way, further dives are planned to search for more parts of it.) The alternative possibility is that antiquity had many more such exotic devices, which have remained unreported, at least in the manuscripts which have come down to us.

That would imply, essentially, that we don’t have a very good idea of what antiquity was like. In my view that is the more rational Bayesian conclusion. It is more likely than thinking that we just lucked out to find this one unique, incredible device. To put it another way, if you found some organic life on a traveling comet, you ought to conclude there is more of that life, or something related, somewhere else.

And to me, the Antikythera Mechanism does not sound like a “lone genius” kind of device: “The gear teeth were in the form of equilateral triangles with an average circular pitch of 1.6 mm, an average wheel thickness of 1.4 mm and an average air gap between gears of 1.2 mm.” (Wikipedia) That suggests it was made by some kind of regular industrial process. It also had some sophistications which modern Swiss watches do not.

What should a Bayesian infer from the Antikythera Mechanism? (Marginal Revolution)

In fact there is written evidence that these sorts of things were a lot more common. Sources describe pneumatic automatons in temples of Alexandra designed by Hero, the most famous inventor of the Classical world, opening doors and mimicking the behaviors of animals. Often these sources have been dismissed as fanciful or imaginary, becase the ancients simply couldn't have done things like this, we assume. But why are so quick to dismiss accounts like this? An earlier paper on the mechansim includes this quote from Cicero:

"Listening one day to the recital of a similar prodigy, in the house of Marcellus, who had been his colleague in the consulship; he asked to see a celestial globe, which Marcellus’s grandfather had saved after the capture of Syracuse, from this magnificent and opulent city, without bringing home any other memorial of so great a victory."

"I had often heard this celestial globe or sphere mentioned on account of the great fame of Archimedes. Its appearance, however, did not seem to me particularly striking. There is another, more elegant in form, and more generally known, moulded by the same Archimedes, and deposited by the same Marcellus, in the Temple of Virtue at Rome. But as soon as Gallus had began to explain, by his sublime science, the composition of this machine, I felt that the Sicilian geometrician must have possessed a genius superior to any thing we usually conceive to belong to our nature...."

The Antikythera mechanism (Understanding Society)

Our perception of history have been clouded by modern notions of eternal and neverending progress. If they could do things like this, we think, then why didn't they keep going and build factories and railroads? But why would they? Such things are not obvious except with the benefit of hindsight.

In a famous paper on the development of the wheel (PDF), the historian Ted Cloak notes that technology does not develop in a vacuum—any piece of technology is part of a complex, integrated whole that emerges piecemeal in ways that are only seem inevitable once they have been invented. Technology is intertwined with the culture that produced it:

I want to draw a general conclusion about culture from this brief discussion of the wheel. Many cultural taxa are, like the wheel, functionally integrated wholes. Kinship systems, social structures, ideologies, modal personalities, and art styles, not to mention languages, can be and are often looked at as such. Indeed, an entire culture can be considered a functionally integrated whole.

As the case of the spoked wheel seems to indicate, however, it is not necessary to conclude that the integration of these cultural systems is necessarily due to the operation of special cultural principles; it may well be that in every case they have evolved bit by bit through the operation of one basic principle, that of Darwinian natural selection, working on the system as it is at the moment, in the total ecological context—including natural and cultural features—with which it has to deal.

Keeping these ideas in mind makes the origins of the Industrial Revolution—like the agricultural, urban and commercial revolutions before them—look less like sudden, inexplicable break from the past and more like the end result of long-term trends that were unfolding over very long periods of time. We just miss it because so much of the past has been permanently lost to us, or else we've been spending too much time looking for our keys under the streelight.


P.S. Couldn't fit this in, but the role of fiber arts in prehistory is not given anywhere near the attention it deserves. Recently Israeli archaeologists found a basket from 10,000 years ago preserved in a cave. You can see from the photo why pottery was't invented until much later on—it wasn't needed! (the Biblical scroll which was also found in the cave got most of the media's attention):

And some bone tools from 40,000 years ago found in the Hohle Fels cave (where the famous Venus was discovered) have now been identified as tools for making rope. They were used for twisting strands of fibers together:

Our stone-age ancestors would have been able to feed plant fibres through the instrument’s four holes and by twisting it create strong ropes and twines. The grooves round the holes would have helped keep the plant fibres in place. The resulting ropes could then have been used to make fishing nets, snares and traps, bows and arrows, clothing and containers for carrying food. Heavy objects, such as sleds, could now be hauled on ropes while spear points could be lashed to poles. A technological milestone had been reached in our development.

Similar devices have been found at many other sites once occupied by ancient humans in Europe, suggesting making and using rope had become widespread in the upper palaeolithic or late old stone age...

Fibers are, of course, especially perishable, but their complexity and sophistication probably meant that there was no need to invent more durable technologies—the kinds that show up in the archaeological record—until much later. In fact, reeds and thatch can produce everything from boats to houses.