Charles Darwin: Bottom-up Thinker

So why is the blog called “bottom-up?” One of the central themes of the blog will be a contrast between two styles of thinking, which I’ll call “top-down” and “bottom-up.” I’ll argue that top-down thinking comes more naturally to people, but that as society grows more complex, bottom-up thinking is becoming increasingly important to understanding the world around us.

I’ll contend that one of the big problems with top-down thinking is a tendency to pay too much attention to abstract arguments and too little to the concrete “facts on the ground.” So rather than launching into a long “bottom-up manifesto,” which would be a little bit hypocritical, let me start with an example of someone who exemplified the bottom-up method of understanding the world: Charles Darwin.

This is a big year for Darwin fans. The British biologist was born 200 years ago, and he published his most famous work, On the Origin of Species, 150 years ago. Although Darwin’s theory of evolution isn’t remotely controversial among people with relevant expertise, it continues to be intensely controversial among the general public, with just 39 percent of Americans saying they “believe in evolution.”

This is puzzling. Darwin’s argument is compelling, and in the last 150 years biologists have accumulated overwhelming evidence in its support. (I’m not going to belabor the point, but if you’re not already convinced I encourage you to read Dawkins and Dennett.) Moreover, the basic theory has a remarkable elegance and simplicity. It’s less complicated than Maxwell’s equations of electromagnetism, for example, which were published around the same time. Yet you’re not likely to meet people at parties convinced that Maxwellism is a “theory in crisis.”

So what’s going on? One possible explanation is that people perceive the theory of evolution as a threat to their religious beliefs. There’s certainly something to this, but it can’t be the whole story. Only 55 percent of people who seldom or never go to church profess belief in evolution—clearly the other 45 percent aren’t all religious zealots. Moreover, the Catholic Church itself has concluded that Darwin’s theory can be reconciled with Christian faith. If the Pope can do it, you’d think other Christians would be able to follow suit.

I think one of the most important factors is that people have a strong inclination to think in terms of stories involving anthropomorphized actors. Historically, when people lacked a good explanation for some phenomenon, they would often invent a sentient being whose actions could explain it. When primitive tribes lacked a naturalistic explanation for weather patterns, they often postulated a deity that controlled the weather and they would perform rain dances or give offerings in hopes of influencing it. When they lacked naturalistic explanation for diseases, they postulated the existence of demons, witches, or other malevolent forces to explain them.

Fortunately, when naturalistic explanations for these phenomena came along, most people didn’t reject them on religious grounds. Today there’s no shortage of people who believe in demons and witches, but most of them will still take their kid to the doctor when he gets sick. So why hasn’t the same thing happened with evolution? I think the key difference is this: the germ theory of disease offers a new, tangible thing—the “germ”—that makes you sick. Likewise, the stylized weather map you see on television, with its cold fronts and low pressure systems, offers people a plausible story about what caused the weather to change.

In a sense, people simply traded in the old, supernatural entities—demons, witches, Tlaloc—for new, natural ones: germs, low pressure systems, cold fronts. I doubt one person in ten could give a detailed explanation of how germs make people sick (come to think of it, I’m not sure I could) but this doesn’t matter. Most people are happy to simply accept the formulation “germs cause sickness,” without delving any deeper.

The problem is that it’s almost impossible to frame Darwin’s theory in these same terms. There are no particular things that “cause” evolution. Darwin’s central metaphor, natural selection, is far too abstract to serve the same role that germs play in the germ theory. And as a consequence, when you try to explain evolution to someone who’s used to thinking about scientific findings in “X causes Y” terms, they often interpret you as saying nothing causes evolution—that the diversity of life is some kind of fluke or accident.

Darwin’s theory is hard for people to grasp because it relies on a subtle, statistical concept of causality. Natural selection happened in a series of infinitesimal steps over a mind-bogglingly long period of time. Our brains, which are optimized for thinking about the people around us and how to get our next meal, are bad at thinking about phenomena like that. People find it easy to understand a single step in the evolutionary process, but they find it hard to imagine that millions of tiny steps, undirected by any intelligence, could in the aggregate produce trees and elephants and people.

Unfortunately, the universe doesn’t care if we find it counter-intuitive. Evolution happened, and human beings wanting to study it effectively have to learn to think about the world in ways that don’t come naturally. Moreover, evolution isn’t an isolated example: modern societies have many complex, decentralized systems whose understanding requires us to think in counter-intuitive ways.