Book Review: Darwin’s Dangerous Idea

Darwin’s Dangerous Idea: Evolution and the Meaning of Life by Daniel Dennett

I’ve been reading Dan Dennett’s oeuvre out of order: by reading Intuition Pumps first, I’m already familiar with many of the arguments and thought experiments in Darwin’s Dangerous Idea.  For example: the Library of Babel, based on a short story by Jorge Luis Borges, which contains all the books of a certain length for every combination of characters. The Library is truly vast, when you begin to contemplate it: most of the tomes are utter nonsense, but also contained therein is a copy of Moby Dick, and versions of Moby Dick with one typographical error in any spot, and versions of Moby Dick with subtle changes in wording that would be considered improvements. And that would be one small corner of a vanishing part of a sliver of the Library.

The Library is used as an analogy with what Dennett calls “design space”, which contains both the products of natural selection and the products of human culture and innovation; there is no principled difference between the locations in design space. What is different is how one navigates design space. Natural selection randomly samples from nearby points and moves by increments in directions that improve local fitness. Human engineers and artists on the other hand can use rules and heuristics and insights to make giant leaps through design space.

Darwin’s Dangerous Idea can be considered an apology for Darwinism, in the sense of apology as a defense (like Christian apologetics). The dangerous idea itself is that natural selection is a dumb algorithm (a concept unavailable to Darwin himself, as the theory of algorithms is a 20th century artifact). Another idea introduced by Dennett is the distinction between “skyhooks and cranes”. A crane (the construction kind) can be used to lift objects in space (or more abstractly in design space), and most wonderfully can be used to construct ever larger cranes. A skyhook on the other hand is a hook connected to a tether that disappears into the sky. It can also lift things, but is a non-physical miracle. The book then is a series of rebuttals to objectors to Darwinism that think that to explain entities like human beings, one needs skyhooks. Examples include language and consciousness.

Darwin’s Dangerous Idea isn’t the final say in how dumb natural selection can bring about bizarre phenomenon like language or consciousness (it would be rather amazing if it did and was just sitting there for the past 20 years!), but rather shows that supposed skyhook rebuttals of “This far but no farther” sort have fatal flaws. We don’t know how to build an AI that would be conscious, but Dennett shows that certain objects of the form that it could not be done even in principle are lacking.

Just because the dangerous idea of algorithmic natural selection is so powerful however (Dennett calls it a “universal acid”) does not mean that it’s the be all and end all of explanation. He concludes with some chapters on morality, about how moral systems need to have a naturalistic basis but to merely say “What as selected for is right” is to commit the naturalistic fallacy. There is no easy way out for ethics.

As a popular book on the philosophy of biology, Darwin’s Dangerous Idea is a nice complement to earlier works like Dawkins’ The Selfish Gene, which Dennett quotes regularly in the book.

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