Homo sapiens is the only species on planet Earth to have experienced three phases of evolution: the standard biological one, driven by mutation and natural selection; gene-culture coevolution; and now the period of evolution driven primarily by culture. This is how chapter 10 of Kevin Laland’s Darwin’s Unfinished Symphony: How Culture Made the Human Mind, begins the transition to the author’s discussion of that very last, novel, and crucial phase. (More entries in this ongoing series here.)
It’s an obviously crucial topic for a variety of reasons. First off, to help explain why on earth we evolved such large and metabolically expensive brains. Keep in mind that the human brain accounts for only 2% of our total body weight, and yet it consumes a whopping 20% of our daily caloric intake. (It’s unfortunate that thinking harder doesn’t lead to weight loss…). Second, as Kevin has documented in the previous chapters of the book, it is our capacity for social learning (and teaching) that accounts for the incredible success of our species, as the third mode of evolution is what has made possible for us to build giant cities, go to the Moon, and waste our existence on social media.
Kevin begins by addressing a related question: why did it take so long for our species to develop complex civilizations, while hunter-gatherer societies still today have very limited technology and simple cultures? The likely answer has to do with the severe limitations imposed by a hunter-gatherer lifestyle. To begin with, of course, hunter-gatherers have to be constantly on the move, changing base location once the local resources are depleted. This means that it is impossible to settle down long enough to develop a large population size and the division of labor that foster new technological developments. And even if some new technology were to be developed, it would have to be of limited size and complexity, again because the entire population has to pick up and move every few weeks or so.
Similarly, in hunter-gatherer societies the birthrate is typically low, with new pregnancies well separated in time, as a human female cannot carry and care for many small children when the group is constantly on the move. Small population size and temporary abodes also means no accumulation of wealth of the kind that makes division of labor possible, leading in turn to the origin of specialized classes of workers that can rapidly accumulate specific technical knowledge over few generations.
“This helps us understand why hunter-gather technology was only slowly changing for such a long time, and also why, even today, many small-scale societies possess limited technology. Hunter-gatherers are effectively trapped in a vicious cycle that severely constrains their rate of cultural evolution.” (p. 248)
That’s also why the invention of agriculture, which took place multiple times after the last Ice Age, is tightly linked with the origin of complex human technological cultures. The reason agriculture did not originate earlier is because the conditions following that Ice Age, about 11,500 years ago, have actually been the most favorable — climatically speaking — for such an event over the last two million years of hominid evolution. And before then our ancestors simply did not have the required brain power and ability to communicate through language.
Plant and animal domestication of some sort preceded the full blown agriculture revolution, and the first plants to be domesticated were annuals, characterized by a rapid life cycle and hence easy to select artificially. These included peas, wheat, rye, barley, and maize. A new form of wheat, for instance, appeared around 9,600 BCE in the eastern Mediterranean region. Maize was farmed in southern Mexico around 9,000 years ago. Millet appeared in China between 10,300 and 8,700 years ago, rice around 9,000 years ago.
The invention of agriculture was not without its own problems. The more stable source of food led to population explosions, which in turn caused periodical famines. Indeed, the archeological data show that Europeans became shorter by about 7 cm. between 2,300 and as little as 400 years ago, because of poor nutrition.
As Laland points out, agriculture is a great example of niche construction on the part of human beings. The old idea, in ecology, that niches are “out there,” waiting to be filled by new species of organisms, has been questioned for some time now. Rather, living beings actively alter their environment, co-evolving with it, if you will. By far the most spectacular example in the history of earth is the fact that we have high levels of oxygen in our atmosphere, a byproduct of photosynthesis, an organic process that has made animal life possible in the first place.
Since agriculture was not an unqualified good, it is reasonable to ask how come the new mode of life largely and rapidly replaced the old hunter-gathering. Kevin offers two main reasons: first, agriculturalists simply outbred hunter-gatherers, because of the larger population size made possible by a sedentary lifestyle. Before the advent of agriculture the world’s human population had stabilized at around one million people. By the time of the Roman empire it was up to 60 millions.
The second factor was a wave of innovations triggered by agriculture. For instance, the invention of the wheel, which appeared simultaneously in Mesopotamia, Russia and central Europe around 5,500 years ago. The first organized religions also sprang in agricultural societies, with different cultures, predictably, worshiping gods related to agriculture: Inti, the sun-god of the Inca; Renenutet, the Egyptian god of harvest; Ashnan, the goddess of grain in Mesopotamia; and Ceres, the Roman goddess (counterpart of the Greek Demeter) who was credited with the discovery of wheat, the invention of ploughing, the yoking of oxen, and similar.
Here is another way to appreciate the difference between pre- and post-agriculture humanity:
“Prior to the advent of agriculture, each population would have possessed at most a few hundred types of artifacts, while today the inhabitants of New York are able to choose between 100 billion bar-coded items. … One recent estimate of the amount of information now stored on the internet is 1,200,000 terabytes.” (p. 263, 269)
Kevin points out that all this innovation has had dark sides, including environmental destruction, not just today, but throughout the last 10,000 years or so, with humanity being responsible for countless extinctions of other species; as well as of course the scale of war that technology has made possible; and the increasing inequality (compared to hunter-gatherer societies) among human beings themselves. It seems like both natural and cultural selection don’t really care about ethical considerations, although of course we should. But that’s another story.