Threshold 6—What Makes Humans Different?

Threshold 6—What Makes Humans Different?

Lecture 20

[Big history] encourages us to think seriously about questions such as the meaning of being human. And it encourages us to think that they are not just metaphysical or philosophical questions, but they are questions to which there may be good, rigorous, evidence-based scienti c answers.

What does it mean to be human? The previous lectures described the history of life on Earth and the evolution of our own ancestors through the adaptive mechanism of natural selection. The next group of lectures takes us across a new threshold, describing the creation of our own species and the earliest stages of human history. But before we can determine when our species appeared we need some clear ideas about the features that distinguish us from other hominines. The differences, we will see, are fundamental.

We have seen how similar we are to other living organisms. Now we must ask: What makes us so different that our evolution counts as a fundamental turning point in the history of our planet? One distinctive feature is the amount of energy we control. Eric Chaisson has calculated that about 20,000 ergs per second per gram ow through large-bodied animals such as apes. He calculates that modern humans use on average 25 times as much energy (500,000 ergs/sec/gram; calculated by dividing total energy consumption by the number and mass of human beings; Chaisson, Cosmic Evolution, pp. 136–39). Though approximate, these gures clearly point to a profound difference between us and all other animal species.

Human control of energy increased slowly at rst, then accelerated. In the Paleolithic era, more than 10,000 years ago, humans probably used enough energy to stay alive with a small surplus, perhaps 3,000 to 5,000 kilocalories a day. Early agriculturalists may have used up to 12,000 kilocalories a day. Today, each of us uses on average 230,000 kilocalories a day. In contrast, chimp use of energy, like that of most other species, has remained stable. More energy allowed humans to multiply. Today, there are a few hundred

thousand chimps (and their numbers are dwindling rapidly). But there are 6 billion humans. More people and more energy help explain why modern human society is so complex.

Why does our species control such extraordinary amounts of energy? We have seen that all living organisms explore their environments in the search for the energy they need. But humans apparently do this peculiarly successfully. Indeed, we seem to continually nd new ways of getting energy and materials from our environment. Our adaptability was apparent even in the Paleolithic era, the oldest era of human history, as migrations took our ancestors into many different environments and to all continents except Antarctica, because each new environment required new ways of controlling energy.

In summary, most species, like the Galapagos nches, develop a way of exploiting their environment and survive only as long as their technique works. In contrast, humans constantly develop new ways of extracting resources from their environments.

Our extraordinary ability to adapt, and to keep adapting, makes us very powerful. Our astonishing control of the planet’s resources is now affecting other species. According to some estimates, we may be controlling 25%–40% of all the energy that enters the biosphere through photosynthesis. This leaves less energy for other species, which may explain why other species are dying out at a rate comparable to the ve or six greatest extinction episodes of the last billion years. We may be strange even on cosmological scales. For almost 50 years, astronomers have searched, without success, for evidence of other organisms with a similar level of technological creativity. Perhaps we are unique on galactic scales!

Why are we so good at adapting? There is no universally accepted answer. However, lines of argument in several disciplines, from psychology to anthropology and archaeology, seem to be converging on some revealing answers. What follows is based on some of this scholarship. I will argue that

If chimps function mostly like stand-alone computers, modern humans are networked.

our species is endowed with a unique and extraordinarily powerful adaptive mechanism: “collective learning.” That’s a term I’ll use a lot so I need to explain it carefully.

Adaptation by natural selection is slow. Because it depends on genetic changes, it can take hundreds or thousand of generations for changes to evolve and spread. But there are other ways of adapting. Organisms with brains can change how they relate to their surroundings within a single lifetime. This is “individual learning.” It works faster than natural selection, but it has limitations. Individual learning is costly because brains consume lots of energy and have to be fed. Emperor Hirohito, who was a biologist, once studied a species of sea slug that illustrates the point nicely by eating its brain once it no longer needs it. Individual learning is not cumulative. Most of what an individual learns cannot be passed on to others, so each individual has to start from scratch.

Now imagine a species in which individuals could pass on most of what they learned to other members of their species. Here we would have a third, and much more rapid, way of adapting—because what each individual learned would then be stored within the entire community. This is the unique gift humans acquired with human language. Simple forms of communication depend on one-to-one correspondence, like the warning call of a vervet monkey: A bark-like call means a leopard, while a sort of stutter means a snake. Such utterances can communicate about as much information as an ambulance siren. Most animal languages seem to take this form.

However, humans are capable of using “symbolic language.” Symbols are arbitrary signs that can group many observations or ideas within larger categories and can therefore rearrange information in many new ways. While a vervet can say “leopard,” it cannot say exactly where the leopard is or what it is doing. Symbols can convey such information. They can even refer to things that are not present (such as the leopard I saw yesterday) or things that may not exist (pink elephants or Santa Claus).

Human languages also have elaborate grammatical systems that greatly enhance their ef ciency. Grammar lets us arrange symbols in almost in nite con gurations so humans can use word pictures to convey large amounts of

complex information with great precision. Unlike a vervet, a human could explain, for example, that: “My cousin was killed by a cat-like predator at the water hole one mile away to the south of the volcano.”

Symbolic language allows humans to exchange so much information so precisely and so rapidly that more information is transmitted than is lost. As a result, large stores of information can begin to accumulate within the community as a whole. If chimps function mostly like stand-alone computers, modern humans are networked. Each of us has access to a vast communal database of information about how to adapt to our environment.

I call this unique form of adaptation “collective learning.” If this line of argument is correct, it suggests that collective learning is what explains our exceptional ability to adapt. It is what makes our species unique on this planet, and it explains why human history represents a new level of complexity. Note that this argument does not yet count as an established orthodoxy, though many researchers are converging on some form of it.

Note, also, that it does not depend on individual humans being smarter than individual apes. It is the sharing of information that makes us different. Humans, unlike apes, face their environments armed with a vast amount of information accumulated by millions of individuals over many generations. Collective learning explains why only humans have a history of constant change, as humans have accumulated more and more information about the world they inhabit. Indeed, human history is all about the many changes made possible by our capacity for collective learning. Collective learning explains why we have gotten better and better at extracting energy and resources from the environment and why, collectively, we have become one of the most complex entities in the Universe.

This lecture has argued that we are different because we have access to a new and uniquely powerful adaptive mechanism: collective learning. How and when did our ancestors rst acquire this unique ability? That is the question tackled in the next lecture.

Essential Reading

Supplementary Reading

Questions to Consider

Christian, Maps of Time, chaps. 6, 7; pp. 171–76. Lewin, Human Evolution.

Deacon, The Symbolic Species. Pinker, The Language Instinct. Tomasello, The Cultural Origins. Wright, Nonzero.

1. What evidence is there that our species is radically different from other hominines?

2. What is “collective learning,” and why does it give our species such a striking ecological advantage?