Modern Human Behaviour

One of the major issues in palaeoanthropology and archaeology is when our hominin ancestors became like us. Humans living today have developed the capacity for ‘modern behavior'. Modern behavior can be recognized by creative and innovative culture, language, art, religious beliefs, and complex technologies (d'Errico & Stringer 2011). One of the evolved capabilities underlying modern behavior is the ability to communicate habitually and effortlessly in symbols. The pervasiveness of symbolism in present-day human culture is the reason why archaeologists frequently search for artifacts that reflect ‘symbolically mediated behavior' (Henshilwood & Marean 2003). Modern behavior also consists of other components such as advanced problem solving and long range planning abilities (Wynn & Coolidge 2011). Archaeological artifacts that were produced by thinking ahead of future actions, anticipating problems and preparing responses provide evidence for modern planning abilities (Wadley 2010).

Traces of 'Modern Behavior' in the Archaeological Record

There is lively debate and divergent points of view on the appropriate markers for modern behavior in the archaeological record (Nowell 2010). Many discussions do not use theoretically developed standards such as symbolism or planning capabilities to identify modern behavior, but rely on the archaeological record itself as guide. Modern behavior has, for example, been inferred from certain traits in the archaeological record. These traits include standardization in artifact types, blade technology, worked bone and other organic materials, personal ornaments and art or images, structured living spaces, ritual, economic intensification, enlarged geographic ranges and expanded exchange networks (McBrearty & Brooks 2000). The relatively sudden appearance of such traits as a group or package in the archaeological record of the European Upper Palaeolithic has been interpreted as evidence for the onset of modern behavior (Klein 2008). This trait list approach to identify the origins of modern behavior has been criticized because the archaeological record of only one region, the Upper Palaeolithic of Europe, is used as a standard to infer modern behavior for all other time periods and areas (Deacon 1979, Henshilwood & Marean 2003, Shea 2011).

When the standard of symbolism is applied, it can be shown that artifacts of a clearly symbolic nature appear only after 100,000 years ago (Henshilwood et al. 2002, Henshilwood et al. 2004, d'Errico et al. 2009, Texier et al. 2010). These artifacts include beads as well as ochre and ostrich eggshell with geometrically engraved patterns. Obvious symbolic artifacts do not occur consistently in the archaeological record between 100,000 and 50,000 years ago, and disappear periodically (Hovers & Belfar-Cohen 2006). The fluctuating presence of symbolic artifacts may be related to changing climate and its effect on population sizes. Or perhaps it is only when ornaments with culturally dictated, three dimensional form, figurative art, depictions of mythical imagery, and musical instruments, associated with the Upper Palaeolithic of Eurasia appear, that ancient people truly became like us (Conard 2008, 2010). The absence of symbolic artifacts does not necessarily indicate the absence of symbolic capacities. It may be that ancient people used rituals, such as scarification and body painting, and objects and ornaments of perishable material that did not leave traces in the archaeological record to express their symbolic intentions. It should also be kept in mind that the presence or absence of various modern behavioral traits can be ascribed to climatic change, group size, and cultural exchange rates, rather than a lack of capacity for modernity (Richerson et al. 2009; Powell et al. 2009).

The evolution of modern planning capabilities can be investigated by analyzing the decision steps used to produce ancient tools. There are, for example, many different ways of making stone artifacts. Over the last 200,000 years a variety of reduction techniques in different combinations were used to make stone tools. This resulted in different techno-complexes, but all with the same degree of complexity. This may mean that humans had essentially modern cognitive capabilities for this period of time (Shea 2011). Using variability in stone tools as a marker has the advantage of including the most ubiquitous and widely studied type of material culture in the archaeological record in the search for modern behavior (Nowell & Davidson 2010). Advanced planning abilities were necessary to produce some ancient hunting weapons. For at least the past 200,000 years hunting implements were made by mounting sharp stone tools on a shaft with the aid of adhesives. The backed artefacts from the Howiesons Poort, dating to around 65,000 years ago in South Africa, are examples of such hafted stone tools (Wurz & Lombard 2007, Figure 1).

Figure 1

Possible hafting arrangements of Howiesons Poort backed artefacts. From left to right: diagonally hafted as tips or cutting barbs, transversal and back to back hafting.

© 2012 Nature Education Drawings by L. Davis after Nuzhnyj 2000. All rights reserved.

Microscopic analysis of Howiesons Poort backed tools from Sibudu Cave in KwaZulu Natal, South Africa, revealed hafting microtraces associated with microresidues of ochre and acacia gum (Lombard 2008). Lyn Wadley and her team experimentally produced adhesives using these materials, and tested how to haft stone tools to shafts. They found that several ingredients, including ochre, plant gum, and fatty substances were combined to produce the compound adhesive. In addition, several procedures and complicated use of fire, or pyrotechnology, had to be manipulated to achieve the appropriate consistency for an adhesive that would successfully join the tool to the haft when thrown (see Figures 2 and 3). The cognitive strategy used to produce and manipulate the adhesive in the Howiesons Poort 65,000 years ago indicates multitasking and planning capabilities typical of modern people (Wadley et al. 2009, Wadley 2010).

Figure 2

Experimental production and controlled heating of compound adhesive, incorporating ochre, acacia gum, and fat.

© 2012 Nature Education All rights reserved.

Who, When and How?

There is no straightforward relationship between the appearance of particular archaeological signals of modern behavior and certain kinds of fossils. Some see the development of modern behaviors as a late phenomenon, dating to 50,000 years ago, not related to the speciation of anatomically modern humans (Klein 2009). However, many archaeologists associate the development of modern behavior with anatomically modern humans or Homo sapiens who emerged in Africa around 200,000 years ago, during the Middle Stone age period. The picture is not clear, as modern behaviors have also been linked to the Neanderthals of Europe and hominin ancestors living prior to 200,000 years ago (Deacon & Wurz 2001, Zilhão 2007, d'Errico et al. 2009, d'Errico & Stringer 2011).

When considering when and how modern behavior developed, it is essential to take into account how the brain could have evolved to support modern capabilities. Modern cognitive capacities depend, in part, on an evolved, specialized neural architecture. Unfortunately changes in brain size and shape that can be inferred from hominin fossils provide no clear evidence for the origins of modern behavior. Evolutionary biology and neuroscience studies suggest that hominin symbolic communicative capabilities co-evolved with the brain, resulting in some parts of the brain becoming proportionally larger (Deacon 1997). Humans have a larger prefrontal cortex than other primates and this probably enabled some of the neural connections necessary for generating abstract symbolic concepts and planning tasks. The evolution of human complex functional neural organization may have been a long-term process, involving at least a million years (Deacon 2010). There is also the view that modern neural organization is the result of a relatively sudden genetic mutation that took place in populations from Africa only 50,000 years ago (Klein & Edgar 2002). Research into the origins of modern behavior must also be integrated with theories from cognitive science in which the relationship between brain architecture and cognitive function is investigated (Davidson 2010). An example is the interpretation of archaeological artifacts from the perspective of the executive function and working memory model (Wynn & Coolidge 2011). This model explains how complex cognitive tasks such as planning and learning rely on the mind's ability to temporarily focus on, store, and manage information. According to this particular theory, a set of interlinked capabilities evolved, probably after 100,000 years ago, to allow enhanced working memory.

Blombos and the Origins of Modern Behavior

At the beginning of this millennium, the unexpected discovery of personal ornaments and art older than 70,000 years ago — shell beads and engraved ochre — at Blombos Cave on the southern Cape coast of South Africa, initiated a paradigm shift in thinking about the origins of modern behavior. Prior to this discovery, most scientists considered the birthplace of humans with symbolic capabilities as Upper Palaeolithic Europe (~40,000 years ago), because the earliest art and personal ornaments were found there. The finds from Blombos encouraged scientists to reconsider earlier suggestions that modern behaviors were also associated with the Middle Stone Age of Africa.

Blombos Cave yielded a large collection of tick shell (Nassarius kraussianus) beads — forty-nine intentionally perforated shell beads were found in layers dating to 77,000 years ago (Figure 3a). The shell beads were excavated in clusters of 2 to 17, and each cluster was similar in size, shade, use-wear pattern, and perforation size. The shell walls were pierced through the opening with a sharp bone point and then strung and worn. Some of the beads have traces of ochre inside and on the worn facets that could have been caused by a piercing instrument covered in ochre, or rubbing against an ochre covered skin (d'Errico et al. 2005). Perforated marine shells similar to those from Blombos have also been found in caves from North Africa and the Middle East. Shell beads are of the earliest evidence for personal ornaments, dating to between 100,000 - 70,000 years ago (d'Errico et al. 2009).

Figure 3a

Nassarius kraussianus beads from the 77,000 year old layers at Blombos Cave, South Africa.

© 2012 Nature Education All rights reserved.

The earliest evidence for abstract designs also comes from Blombos Cave. The most impressive find is a dark red rectangular slab of ochre (75.8mm x 34.8 mm x 24.7 mm) with a complex cross-hatched engraved design. The pattern was created using a stone tool by initially engraving the longer parallel lines, whereafter the oblique lines were produced. The last step was to engrave the superficial single line that crosses the oblique lines perpendicularly. Other engraved ochres have been found in earlier layers of Blombos Cave, emphasizing this site's remarkable potential to understand symbolic behaviors of the past (Henshilwood et al. 2009).

The extraordinary discoveries from Blombos Cave and the other examples discussed here show that the most fruitful ways of identifying modern behavior in the archaeological record have been through artifacts that demonstrate symbolism and complex planning abilities. The challenge for future research is to expand archaeological criteria for modern behavior that are fully integrated with neuro-evolutionary theory and cognitive science.

Figure 3b

A slab of ochre with a cross-hatched designed, evidence for abstract cognition.

© 2012 Nature Education All rights reserved.

Hominin - Humans and the immediate ancestors of humans, excluding chimpanzees and gorillas.

Symbol - A sign that can only be understood through a social convention or rule created by people. There is for example nothing concrete in the natural world that relates to a word like ‘hot' or a gesture for ‘excellent.'

Upper Palaeolithic - The time period in Eurasia dating to between 40,000 and 10,000 years ago. It is associated with modern Homo sapiens.

Stone tool techno-complex - A stone tool assemblage dating to a specific period of time that display the same production techniques and types.

Middle Stone Age - The time period in sub-Saharan Africa that occurred between 280,000 and 22,000 years ago. It is associated with modern Homo sapiens.

Executive function and working memory model - Working memory refers to the mind's ability to hold information needed for complex tasks. Executive function encompasses the brain's ability to plan and strategize.