Tracking our earliest human ancestors from microscopic remains

 In an article recently published in Quaternary Research (QR), Magnus Haaland and his colleagues at The Centre for Early Sapiens Behaviour (SapienCE) demonstrate how microscopic sand grains can provide us with important information about human campsite activities and behavioural development far back in time. Dr. Haaland's study shows how microscopic archaeological fragments can be essential for obtaining a more comprehensive picture of the everyday life of the first modern humans.

Blombos Cave: the cradle of human culture?

"Until recently, we’ve known very little about the camps people lived in 70,000 years ago. We have obtained knowledge about what they ate and what tools they made, but we’ve had few clues as to how they chose to organise their settlements or how they moved around in the landscape," says Dr. Haaland.

According to Dr. Haaland, getting a better understanding of prehistoric settlement patterns and occupation patterns is important because it tells us something fundamental about the daily routines – the lifeways – of early hunter-gatherers. Due to the new archaeological methods Dr. Haaland has developed, we are now able to get one step closer to our most distant ancestors who lived in South Africa between 100,000 and 70, 000 years ago.

The archaeological fragments on which Dr. Haaland has conducted his research were found in prehistoric cultural layers and sediment in Blombos Cave in South Africa. He still remembers the experience he had when he first stood in front of the more than 2-meter-high sediment wall in the world-famous cave nearly 12 years ago.

 "I remember standing there for a long time looking at the stratigraphy that had been uncovered by archaeologists over a period of more than 20 years. There were hundreds of them! And the colours and content were all different, with some of them extending out across the whole of the cave floor. Although I was able to recognise animal bones, shells and stone tools between the layers, most of them were so fragmented that I didn't really know what I was looking at," says Dr. Haaland.

The world's first objects of art

We now know that the layers which were excavated in Blombos Cave were mainly formed by the people who started living there between 100,000 and 70,000 years ago. This cave, which is located on the coast of South Africa, has previously turned out to be unique for archaeologists who are studying the very first humans.

Under the leadership of Christopher Henshilwood, UiB archaeologists have found the world's first objects of art, the world's first drawing, the advanced use of pigments and some of the oldest items of jewellery known in the history of mankind.

In short: this cave has been the subject of considerable attention because the people who lived there were unusually creative and engaged in complex activities, at a much earlier time than has previously been thought possible.

"When you enter this cave, it's almost like walking into a time machine where time has stood still for tens or thousands of years. But some of the material we are finding looks like it was placed there last year, so the cave has excellent preservation conditions," says Haaland.

From large to small

Until about ten years ago, the archaeologists involved in excavations in Blombos Cave focused primarily on the large, visible artefacts left by our ancestors – in other words, the items that are large enough for us to see with the naked eye. However, Haaland wanted to find answers by studying the smallest fragments. This is why he decided to write a doctoral thesis about how archaeologists can study human behaviour by looking at the microscopic signature different types of activities left behind. In other words, all the broken down material that humans left behind, but which we cannot identify unless one employ laboratory techniques and microscopes.

"I simply wanted to find out what all the tiny fragments hiding in the sand might be and what they could possibly tell us about human activity," says Dr. Haaland.

But what started out as a relatively simple idea would soon prove to be far more challenging than Dr. Haaland initially thought. He explains that the complexity of this work could be compared to doing a jigsaw puzzle containing a million pieces without knowing what the original picture looked like.

“Furthermore, you need to imagine that half the pieces might have been eaten, blown away or burnt. Some of the pieces we have found no longer have impressions that are visible, while the colour of others may have changed. To put it simple, this was the starting point when I began studying the sediment in Blombos Cave," says Dr. Haaland.

People in the sand

Studies of people who lived a long time ago show that humans always have been complex beings. Consequently, Dr. Haaland believes that it is important to look systematically for all possible clues – and not limit ourselves to any selected categories of findings –  if we are to be able to form a more detailed picture of life in the distant past.

"Even the tiniest clues at an archaeological site can tell us a lot about what people did, but this type of work requires a completely different approach to archaeology what is normal," says Dr. Haaland. And this is where the geoarchaeological analysis methods used by Haaland and his colleagues come into play.

"Geoarchaeological analyses of archaeological cultural layers involve using methods and techniques that were originally developed in connection with geology, sedimentology and geochemistry. This means that in a cave like Blombos Cave, where there are layers consisting of many different types of sediments, we have to carefully extract samples from each of these layers and then try to explain them as best we can," says Dr. Haaland.

He says that the aim of such analysis is first to identify the fragment and then find out where they originally came from and how it ended up in the cave. During this investigative process they are also looking at how well preserved the fragments are, and what kind of degradation process might have been involved. In practice this involve identifying, mapping and analysing fragments of a range of different materials, including bone, wood, ash, charcoal, pigments, plants, debitage after tool production and shellfish.

"We know, for example, that shellfish do not naturally live in caves, but they were regularly picked up and eaten by hunter-gatherers who lived along the coast. When we find thousands of tiny shell fragments in one part of the cave, this tell us something about what the people who lived there brought back to the cave – such as shellfish, how much they ate, whether or not they cooked the shell. The breakage patterns on the shell fragments can also be used to assess trampling intensity and a cluster of shellfish can indicate food waste disposal strategies " he says.

Dr. Haaland emphasize that this type of information can reveal every-day moments of how these people chose to organise their camp sites and what they did while they lived there.

Interdisciplinary scientific approach 

The systematic use of geoarchaeological sediment analysis on archaeological cultural layers is still in its infancy. During the last 20 years a there has been important methodological developments that has been vital for producing sound, verifiable research results. Several of the methods used by Dr. Haaland and his colleagues were well-tried and developed more than 50 years ago in conventional geo-scientific disciplines. However, many of them were primarily developed with the intention of documenting natural and predictable phenomena rather than unpredictable human activities. Dr. Haaland admits that one of the biggest challenges they are facing is the fact that prehistoric humans – just as the ones living today -  were extremely unpredictable.

“We simply have a tendency to do a lot of really strange things in those places where we reside for any length of time. As a result of this, no cave or cultural layer is ever completely identical and the internal structure of cultural layers from the Stone Age will consequently be as complex as the people who made them," says Dr. Haaland.

He therefore maintains that if we wish to interpret human behaviour on the basis of tiny cave fragments, we cannot blindly use analytical methods which were originally designed to explain much simpler natural processes.

"It is essential that we combine geological and geochemical techniques in a laboratory with the archaeological observations made in the field," says Dr. Haaland.

It is also important to have good knowledge about how traditional societies organise their campsites and settlements, for example by conducting ethnographic observations. Dr. Haaland says that often they also have to make their own reference material and compare it with the archaeological material.

"In many ways, this work is similar to the type of work often associated with police investigations, combined with a good dose of humility and curiosity. However, the big difference is that we arrived at the scene 70,000 years too late!

A cultural revolution 70,000 years ago

When the researchers compared the earliest stages of use in Blombos Cave with later stages, they realised that the people who lived there must have experienced some type of cultural revolution. The archaeological evidence show that the people that lived in the cave during the oldest phase, around 94,000 years ago left behind very few complex cultural expression. The people that lived in the cave some 25 000 years later, however, are today recognized as some of the earliest makers of art and jewellery in the world.

The question being posed by the archaeologists has therefore been: what happened to the people between these periods of occupation? How do a group of hunter-gatherers go from being completely uninterested in decorative items and artistic expression, to suddenly producing them in huge quantities? Something must have changed, but what?  Dr. Haaland has also been curious about this.

"When I looked at the archaeological fragments from these very interesting periods, I suddenly saw a very marked shift in the pattern of occupation and activity in the cave.”

In his opinion it would appear that the groups of hunter-gatherers who lived during the oldest period stayed in the cave for longer periods of time before moving on. On the other hand, during the younger phase, we see a completely different pattern of cave occupation.

“During the younger period it would appear that the cave was visited far more frequently, but that each visit did not last very long. It was when we made this simple but very important discovery that we asked ourselves: could there be any connection between these two patterns?

Settlement activity during the Stone Age – a source of new knowledge

During the period under discussion here, that is the period between 50,000 and 100,000 years ago, it is thought that the most important factor that determined how long a group of hunter-gatherers would live in one place was the amount of food available in their local environment. The more food available nearby, the more sedentary these groups become. If this dynamic was also in play around the cave site of Blombos, it is likely that the hunter-gatherers who lived there during the oldest phases of occupation had a completely different subsistence pattern compared to those who lived there during the youngest phase.

We can say that, because our sediment analyses show us that the first group of cave inhabitants was able to live in the cave for long periods of time, they brought back more food and material to the cave, they made huge and long-lasting fires and they performed a range of different domestic activities at the site, before they moved on. The group occupying the cave during the youngest phase, however, seems to have had an opposite use of the cave. They were only visiting for maybe a few days or a week, they made small fires and left considerably less material, before moving on to their next campsite.

Dr. Haaland also has a clear idea about what might lie behind this change in occupation intensity and mobility pattern. He points out that sea-levels during this period dropped dramatically, which meant that the coastline outside Blombos Cave also relocated.

"During the earliest stage of occupation, Blombos Cave was a coastal site, with good access to marine resources, such as fish, shellfish and seals. We know from ethnographic and archaeological studies that coastal hunter-gatherers are able to settle for longer periods of time on the same spot, because of the amount and predictability of marine food sources.  However, during the younger stage of Blombos Cave occupation, it appears that the sea-level dropped so much that the access to the coast and the sea was greatly reduced. “We have estimated that the hunter-gatherers who lived during this latter period had to walk up to 15 km in order to collect a good fish meal," says Dr. Haaland.

Settlement patterns and mobility strategies

"The cultural layers in Blombos tell us that those hunter-gatherers who had the most complex cultural expressions also belonged to those groups of people who moved around most in the landscape," says Haaland.

In order to understand the role of art and cultural expression among our distant and mobile ancestors, we should probably not view them as some sort of spare time scrap-booking projects. When the residents of Blombos Cave made a piece of jewellery or drew an abstract symbol, it is more likely that they served some type of social and communicative function.

"We know from contemporary traditional and Western societies that the use of decorative items and symbols is a highly efficient way of communicating who you are and what you stand for, both as an individual and as a group. Dr. Haaland believes that in a constantly changing world where access to resources was reduced, the development of more efficient and complex ways of communicating may have been essential in order to survive.

Complex social strategies 

Dr. Haaland believes that if the hunter-gatherer groups around Blombos became more mobile, they also increased the chance of encountering neighbouring groups that also were forced to move quicker through the landscape. In this scenario, it is easy to imagine that these early groups of modern humans had to invent a few new ways to relate to each other. It may have become quite important to develop communication strategies designed to reduce conflict – and to encourage new forms of cooperation across different groups.

"For example, we have no evidence suggesting that hunter-gatherer communities this far back in time were hostile towards each other. Rather, it would appear that they - like many ethnographically known traditional societies – may have developed more complex social strategies in order to survive side by side, for example, by sharing resources and information,” he says.

Dr. Haaland's hypothesis is that the first people who developed art and cultural objects in Blombos Cave did so because the need to cooperate and to relate to other people was more essential for surviving the change in climate and sea-levels at the time.

“Yes, I think it's a likely hypothesis. However, we still need to search for more pieces of this jigsaw puzzle. There are many details that we don’t fully understand, so our investigation will continue" says Magnus Haaland.