August 17, 2010

What the pfc did for early humans

Posted in Language and Myth tagged , , , , at 10:49 pm by Jeremy

This section of my book draft, Finding the Li: Towards a Democracy of Consciousness, looks at how the unique powers of the prefrontal cortex gave early humans the capability to construct tools, exercise self-control, and begin to control aspects of the environment around them.  But most of all it gave them the power of symbolic thought, which has become the basis of all human achievement since then.   As always, constructive comments are welcomed.

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What the pfc did for early humans

Mithen’s “cognitive fluidity” and Coolidge and Wynn’s “enhanced working memory” are really two different ways of describing the same basic dynamic of the pfc connecting up diverse aspects of the mind’s intelligence to create coherent meaning that wasn’t there before.  But what specifically did this enhanced capability do for our early human ancestors?

To begin with, it enabled us to make tools.  It used to be conventional wisdom that humans are the only tool-makers, so much so that the earliest known genus of the species homo, which lived around two million years ago, is named homo habilis, or “handy man.”  Then, in the 1960s, Jane Goodall discovered that chimpanzees also used primitive tools, such as placing stalks of grass into termite holes.  When Goodall’s boss, Louis Leakey, heard this, he famously replied “Now we must now redefine ‘tool’, redefine ‘man’, or accept chimpanzees as humans!”[1] Well, as we’ve seen in the preceding pages, there’s been plenty of work done in redefining “man” since then, but none of this takes away from the fact that humans clearly use tools vastly more effectively than chimpanzees or any other mammals.

Oldowan tools: better than what any chimpanzee can do.

To be fair to our old “handy man” homo habilis, even the primitive stone tools they left behind, called Oldowan artifacts after the Olduvai Gorge in East Africa where they were first found, represented a major advance in working memory over our chimpanzee cousins.  Steve Mithen has pointed out that some Oldowan tools were clearly manufactured to make other tools, such as “the production of a stone flake to sharpen a stick.”[2] Making a tool to make another tool is unknown in chimpanzees, and requires determined planning, holding the idea of the second tool in your working memory while you’re preparing your first tool.  Oldowan artifacts remained the same for a million years, so even though they were an advance over chimp technology, there was none of the innovation that we associate with our modern pfc functioning.  The next generation of tools, called the Acheulian industry, required more skillful stone knapping, and show attractive bilateral symmetry, but they also remained the same for another million years or so.[3] It was around three hundred thousand years ago, shortly before anatomically  modern humans emerged, that stone knapping really took off, with stone-tipped spears and scrapers with handles representing “an order-of-magnitude increase in technological complexity.”[4]

Acheulian tools: improved on Oldowan but stayed the same for a million years

None of these tools – even the more primitive Oldowan and Acheulian – can be made by chimpanzees, and they could never have existed without the power of abstraction provided by the pfc.[5]*   Planning for this kind of tool-making required a concept of the future, when the hard work put into making the tool would turn out to be worthwhile.  As psychologists Liberman and Trope have pointed out, transcending the present to mentally traverse distances in time and in space “is made possible by the human capacity for abstract processing of information.”  Making function-specific tools, they note, “required constructing hypothetical alternative scenarios of future events,” which could only be done through activating a “brain network involving the prefrontal cortex.”[6]

Another fundamental human characteristic arising from this abstraction of past and future is the power of self-control.  As one psychologist observes, “self-control is nearly impossible if there is not some means by which the individual is capable of perceiving and valuing future over immediate outcomes.”[7] Anyone who has watched children grow up and gradually become more adept at valuing delayed rewards over immediate gratification will not be surprised at the fact that the pfc doesn’t fully develop in a modern human until her early twenties.

This abstraction of the future gave humans not only the power to control themselves but also to control things around them.  A crucial pfc-derived human characteristic is the notion of will, the conscious intention to perform a series of activities, sometimes over a number of years, to achieve a goal.  Given the fundamental nature of this capability, it’s not surprising that, as Tomasello points out, in many languages the word that denotes the future is also the word “for such things as volition or movement to a goal.”   In English, for example, the original notion of “I will it to happen” is embedded in the future tense in the form “It will happen.”[8]

This is already an impressive range of powerful competencies made available to early humans by the pfc.  But of all the powers granted to humans by the awesome connective faculties of the pfc, there seems little doubt that the most spectacular is the power to understand and communicate sets of meaningful symbols, known as symbolization.

The symbolic net of human experience

Ernst Cassirer: first to define humans as "animal symbolicum"

A full generation before Louis Leakey realized it was time to “redefine man,” a German philosopher named Ernst Cassirer who had fled the Nazis was already doing so, writing in 1944 that “instead of defining man as an animal rationale we should define him as an animal symbolicum.”[9] He wasn’t alone in this view.  A leading American anthropologist, Leslie White, also believed that the “capacity to use symbols is a defining quality of humankind.”[10] Because of our use of symbols, Cassirer wrote, “compared with the other animals man lives not merely in a broader reality; he lives, so to speak, in a new dimension of reality.”[11]

Why would the use of symbols take us to a different dimension of reality?  First, it’s important to understand what exactly is meant by the word “symbol.”  In the terminology adopted by cognitive anthropologists, we need to differentiate between an icon, an index, and a symbol.  A simple example may help us to understand the differences.  Suppose it’s time for you to feed your pet dog.  You open your pantry and look at the cans of pet food available.  Each can has a picture on it of the food that’s inside.  That picture is known as an icon, meaning it’s a “representative depiction” of the real thing.  Now, you open the can and your dog comes running, because he smells the food.  The smell is an index of the food, meaning it’s “causally linked” to what it signifies.  But now suppose that instead of giving your hungry dog the food, you wrote on a piece of paper “FOOD IN TEN MINUTES” and put it in your dog’s bowl.  That writing is a symbol, meaning that it has a purely arbitrary relationship to what it signifies, that can only be understood by someone who shares the same code.  Clearly, your dog doesn’t understand symbols, and now he’s pawing at the pantry door trying to get to his food.[12]*

A hungry dog doesn't respond to a note saying "food in ten minutes"

To understand how symbols arose, and why they are so important, it helps to begin with the notion of working memory discussed earlier.   Terrence Deacon has suggested that symbolic thought is “a way of offloading redundant details from working memory, by recognizing a higher-order regularity in the mess of associations, a trick that can accomplish the same task without having to hold all the details in mind.”[13] Remember the image of working memory as a blackboard?  Now imagine a teacher asking twenty-five children to come up and write on the blackboard what they had to eat that morning before they came to school.  The blackboard would quickly fill up with words like cereals and eggs, pancakes and waffles.  Now, suppose that, once the blackboard’s filled up, the teacher erases it all and just writes on the blackboard the word “BREAKFAST”.  That one word, by common consent, symbolizes everything that had previously been written on the blackboard.  And now it’s freed up the rest of the blackboard for anything else.

That’s the powerful effect that the use of symbols has on human cognition.  But there’s another equally powerful aspect of writing that one word “BREAKFAST” on the blackboard.  Every schoolchild has her own experience of what she ate that morning, but by sharing in the symbol “BREAKFAST,” she can rise above the specifics of her own particular meal and understand that there’s something more abstract that is being communicated, referring to the meal all the kids had before they came to school regardless of what it was.  For this reason, symbols are an astonishingly powerful means of communicating, allowing people to  transcend their individual experiences and share them with others.  Symbolic communication can therefore be seen as naturally emerging from human minds evolving on the basis of social intelligence.  This has led one research team to define modern human behavior as “behavior that is mediated by socially constructed patterns of symbolic thinking, actions, and communication.”[14]

Once it got going, symbolic thought became so powerful that it pervaded every aspect of how we think about the world.  In Cassirer’s words:

Man cannot escape from his own achievement… No longer in a merely physical universe, man lives in a symbolic universe.  Language, myth, art, and religion are parts of this universe.  They are the varied threads which weave the symbolic net, the tangled web of human experience.  All human progress in thought and experience refines upon and strengthens this net.[15]

Because of our symbolic capabilities, Deacon adds, “we humans have access to a novel higher-order representation system that… provides a means of representing features of a world that no other creature experiences, the world of the abstract.” We live our lives not just in the physical world, “but also in a world of rules of conduct, beliefs about our histories, and hopes and fears about imagined futures.” [16]

For all the power of symbolic thought, there was one crucial ingredient it needed before it could so dramatically take over human cognition.  It needed a means by which each individual could agree on the code to be used in referencing what they meant.  It had to be a code which everyone could learn and that could be communicated very easily, taking into account the vast array of different things that could carry symbolic meaning.  In short, it needed language – that all-encompassing network of symbols that we’ll explore in the next chapter.


[1] Cited in McGrew, W. C. (2010). “Chimpanzee Technology.” Science, 328, 579-580.

[2] Mithen 1996, op. cit., 96.

[3] Proctor, R. N. (2003). “The Roots of Human Recency: Molecular Anthropology, the Refigured Acheulean, and the UNESCO Response to Auschwitz.” Current Anthropology, 44(2: April 2003), 213-239.

[4] Ambrose, S. H. (2001). “Paleolithic Technology and Human Evolution.” Science, 291(2 March 2001), 1748-1753.

[5] Mithen 1996, op. cit., p. 97 relates a failed attempt to get a famous bonobo named Kanzi, who was very advanced in linguistic skills, to make Oldowan-style stone tools.

[6] Liberman, N., and Trope, Y. (2008). “The Psychology of Transcending the Here and Now.” Science, 322(21 November 2008), 1201-1205.

[7] Barkley, op. cit.

[8] Tomasello, op. cit., p. 43.

[9] Cassirer, E. (1944). An Essay on Man, New Haven: Yale University Press, 26.

[10] Cited by Renfrew, C. (2007). Prehistory: The Making of the Human Mind, New York: Modern Library: Random House, 91.

[11] Cassirer, op. cit.

[12] The distinction, originally made by American philosopher Charles Sanders Peirce, is described in detail in Deacon, T. W. (1997). The Symbolic Species: The Co-evolution of Language and the Brain, New York: Norton; and is also referred to by Noble, W., and Davidson, I. (1996). Human Evolution, Language and Mind: A psychological and archaeological inquiry, New York: Cambridge University Press.  I am grateful to Noble  & Davidson for the powerful image of writing words to substitute for food in the dog’s bowl as an example of a symbol.

[13] Deacon, op. cit., p. 89.

[14] Henshilwood, C. S., and Marean, C. W. (2003). “The Origin of Modern Human Behavior: Critique of the Models and Their Test Implications”Current Anthropology. City, pp. 627-651.

[15] Cassirer, op. cit.

[16] Deacon, op. cit., p. 423.

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