The Evolution of Metapopulations and the Future of Humanity

Or: Who's Your Neighbor?



Earlier I put out a call for evolutionary questions, and several of you responded. I will answer them all in the next few days. First off, ETBNC asked:

It's my understanding this species [Homo sapiens] lived in relatively small social groups (of a few dozen) for at least 95% of its existence as a species. For the last 5% of its history these homo sapiens have been trying to live in increasingly large social groups, as much as 6 or 7 orders of magnitude larger. Since homo sapiens is known to be able to modify its behavior patterns in, um, "interesting" ways, such discontinuity isn't that remarkable.

My hypothesis is that small social groups are still the default behavior for the species homo sapiens. . . . Does that seem like a reasonable hypothesis to you?

It is my view that this is absolutely correct and it has important ramifications for modern human existence, which I'll discuss. The earliest evidence for Homo sapiens in Africa is from about 200,000 years ago. The earliest large-scale societies are from about 10,000 years ago. This means that 95% of our history was spent in small, mobile groups living as hunter-gatherers. However, Homo ergaster, Homo erectus, Homo habilis and the Australopithcines would likely have lived in similar small groups. If we include the rest of our family as part of the human lineage than small groups would have been the norm for 99.9975% of our existence. And if we include our common ancestors with great apes then we might as well round up and conclude that human civilization has simply been a calculation error.

This raises two provocative questions: 1) Why after so long did humans begin living in large sedentary groups? and 2) What does this mean for our modern experiment in group living? The answer to the first question is simple: farming. The most recent ice age lasted from around 70,000 BCE to 10,000 BCE. According to genetic evidence, humans first migrated out of Africa between 59,000–69,000 years ago. Archaeologists have found the first evidence of farming and sedentary, long-term habitations from around 10,000 years ago (and most famously in the region known as the Fertile Crescent). These independent pieces of evidence strongly suggest that the ice age played a significant role in some human populations' original migration and subsequent discovery of agriculture. As Jared Diamond has brilliantly summarized in his Pulitzer Prize winning book Guns, Germs and Steel, agriculture then only had to be discovered independently a few times before it could spread across entire continents within a few hundred to a thousand years. Why agriculture wasn't struck upon earlier than 70,000 years ago is an interesting question, which I can follow up on if there is any interest.

However, agriculture proved to be a radically different way of interacting with the natural world, and it's easy to understand how our ancestors could find it so attractive (and also addictive). Up until this time food had never been an issue, that is, if you were hungry you went out and found food. You followed the migrating herds. You lived along rivers teeming with fish. You collected seeds, and grasses and tubers. On occasion there would be a shortage and many of your loved ones wouldn't make it through the winter, but in general a relatively small proportion of your time was devoted to food preparation.

Agriculture required remaining fixed to a certain area. It required daily toil to plow, plant and harvest the crops and, on top of that, there were constant pests and diseases that could decimate what you'd sown. But it offered control. You could store food and ride out long periods of inclement weather that wouldn't have been possible otherwise. It was a devil's bargain and some groups accepted. As Daniel Quinn suggested in his novel Ishmael, the early conflict between the hunter-gatherer way of life and that of the farmer may have been passed on to us through the myth of Cain and Abel.

These sedentary agricultural communities also allowed enormous population expansion. With a controlled reserve of food more people would survive. The population would expand and more food would be grown to compensate. For the first time in human history, people began to be surrounded by strangers in their own community.

But what does this say about human destiny? If our natural habitat is one of small, migrating groups how are we able to live in cities numbering in the millions? Answer: just barely. The most recent World Bank data demonstrate that only a tiny percentage of us live relatively decent lives, economically speaking. 84% of the world population currently lives on only 16% of the world's combined income. To put that into perspective, the richest 1% in the world today makes an average of $24,000 a year. When we think of the super rich we shouldn't think of Bill Gates, we should think of kindergarten teachers.

We are also living amidst a community of strangers. How many of your neighbors have you met? Where are they originally from? What did their parents do? My guess is that most people reading this don't know their neighbors very well at all. This is important when combined with such extreme inequality. Ethical behavior that was honed through group living (see my post on The Evolution of Morality) and that people would normally demonstrate towards a friend or loved one, doesn't apply as strongly towards a stranger. There are very few costs associated with cheating someone in a business transaction if you're unlikely to ever see that person again. This has necessitated blind laws (such as mandatory minimums and three strikes) in order to punish bad behavior that, in our hunter-gatherer days, could have been decided upon as a group. The earliest laws such as the Code of Hammurabi and the Ten Commandments decreed that death was to be the punishment for most infractions. That we've improved remarkably in our clemency isn't so much a testament to our own beneficence as it is a demonstration of just how off balance human civilization has always been.

So the answer is we're managing, but only barely. However, if the history of human civilization is any guide (think Angkor Wat, think Chichén Itzá), once the human population outstrips the landbase needed to support it then collapse is imminent. As I wrote earlier, we are seriously outstripping our global landbase and we're accelerating. It's going to be a wild ride.