Darwin on My Mind

Evolutionary theory best explains how—and why—we reason.

In Why Think? Evolution and the Rational Mind, Ronald de Sousa—a long-time member of the University of Toronto Philosophy Department, now cast out into the knackers’ yard of retirement—discusses two cases of people instructed by God to kill their children. First there was the wretched Texas housewife Andrea Yates, killer of her five kids, who was found guilty of deliberate murder on the grounds that, having got her divine instructions, she planned carefully how she could drown her babies. Second, there was Abraham, no less of a planner and whose son Isaac was saved only at the last moment thanks to another message from above, not to mention a handy ram ensnared in a thicket. The one was condemned for a vile crime; the other is venerated as a founder of no fewer than three different religions. De Sousa remarks: “When enough people share a delusion, it loses its status as a psychosis and gets a religious tax exemption instead.”

At that point, I knew I was going to love this book—and it is indeed a lot of fun. Why Think? is also good and clever. I have always said that the reason why philosophers are so disliked on university campuses is that we are brighter than anyone else and have trouble concealing the fact. Ronnie de Sousa does nothing to change this perception.

Of course, that does not mean that I am going to agree entirely with his book. De Sousa and I are very much on the same wave length: we are both committed evolutionists, and we are both convinced that Darwinism—and this means the theory of natural selection—is an important tool, perhaps the important tool, to be used in analyzing human thinking. While we do start to come apart in places, in other words we are both pretty hard-line Darwinians—with a point of exception to be made in a moment.

The author starts us off with a significant point, namely that most organisms do not think. Most organisms certainly are not rational. Yet they do all right. Moreover, rationality is not necessarily a key to success. Well thought-through courses of action can go wrong; daft decisions can lead to success. How else does one become a university president? De Sousa might have compounded the paradox a bit by pointing out that thinking is expensive. It requires big brains and they in turn demand lots of protein, which, outside modern yuppie societies, generally means meat. As the late evolutionary paleontologist Jack Sepkoski used to say: “I see intelligence as just one of a variety of adaptations among tetrapods for survival. Running fast in a herd while being as dumb as shit, I think, is a very good adaptation for survival.”

So why do we think? I think de Sousa has the right idea, although I would like to see a bit more biology thrown in here. Thinking gives us options—we are not stuck on one course of action, or with very limited strategic alternatives. Of course, as de Sousa points out, this is partly to do with our being social—in a social situation like ours you need big brains to deal with the various relationships and so forth. “Does Jimmie like me?” “Can I trust him?” “Would it be better to work with Mary instead, even though I know she doesn’t much like me?” On the other hand, being social cannot be all. Ants are social and they don’t do much thinking. I suspect that the real importance of thinking is indeed the fact that we need to make choices, but this comes from the fact that we have got ourselves into a situation where making choices counts.

There are two reasons for this in our case. First, there are more choices to be made because we humans have moved into a realm—or realms—where things change constantly. We do not just live in one fixed environment, but rather in environments that vary in food availability, temperature ranges, predators’ threats and much more. These variations require choices by us, but also—and here sociality kicks in—since we cannot go it alone, we have to do it with others and they too are in the choice business and now a lot of the choices do involve working with others. Try putting out a literary magazine on your own.

Second, because of the costs of producing thinkers, humans cannot produce lots of offspring. This in itself means that we have got to have the abilities to raise them successfully. Think of mother ant. She has literally millions of offspring. She sends them out to find food, and to do this they follow chemical (pheromone) trails. It rains and she loses a couple of thousand who cannot find their way home. Who cares? Tant pis. There are always more where they came from. Now think of humans. Having taken my evolutionary obligations seriously, I have five kids. But think of it. A couple set out for McDonald’s. (Alas, even the Ruses are susceptible to advertising and when you have five you give up on wholesome, organic, vegan fare. It is wholesome, greasy hamburgers all the way.) It starts to rain. Even I would regret the diminution of my brood down to three.

All of this finding one’s way home in the rain means thinking. Which means brains and all of the rest—getting on with others, finding protein and so forth. I am not sure if this is really an evolutionary justification for eating Big Macs, but one can say that this is all very much a feedback situation. As we—and, for much of the journey, other higher mammals—went down the path of big brains, we became better able to be thinkers but more dependent on being thinkers. (Incidentally note that there is nothing Lamarckian about this, supposing that thinking in itself led to bigger brains. Rather, selection produced slightly better brains that led to success and so forth.)

De Sousa rightly points to the work and findings of those scientists who are interested in the evolution of thought processes—the evolutionary psychologists—and notes that they have found that human thought is not like the calculation of a perfect, all-purpose computer (the parallel, I suppose many might expect). We think well in situations where thinking well might be of benefit, and not so well when thinking well is irrelevant. This is shown most clearly in those psychological paradoxes where humans perform well on one task and badly on another task, even though formally they are identical. Take for example the Wason test: Given four cards, with a number on one side and a letter on the other, and the distribution D, F, 3, 7, which cards must you turn over to see if the following rule holds true: “If a card has a D on the one side, it must have a 3 on the other”? Now try this one: “Given four drinkers in a bar—beer, lemonade, 25 years old, 16 years old—and if the bar bans drinking among anyone under 18 years old, which equivalent cards must you turn over to see that no one is breaking the law?” Everyone gets the second problem right but most people flunk the first. Why? Simply because, in everyday life, we much more commonly encounter the boozing-type situation than the abstract number-letter situation, and so are better at solving it.

Seizing on the failures of reason, the well-known philosopher of religion Alvin Plantinga—a man who dislikes modern science and loathes and detests (and, if the truth be known, fears) evolutionary theory—thinks that the unreliability of reason in the Darwinian scenario is reason enough to reject evolution and embrace God. Actually, Plantinga is less interested in the specific problems of rationality (as we have been discussing in the last paragraph) and more with the general ways in which natural selection might fail to produce good thinkers. As Plantinga points out, what counts in evolution is success and not the truth. So how can we ever be sure of the truth? Perhaps none of our thoughts can tell. Perhaps none of our thoughts can tell us about reality. Perhaps we are like beings in a dream world:

“Their beliefs might be like a sort of decoration that isn’t involved in the causal chain leading to action. Their waking beliefs might be no more causally efficacious, with respect to their behavior, than our dream beliefs are with respect to ours. This could go by way of pleiotropy: genes that code for traits important to survival also code for consciousness and belief; but the latter don’t figure into the etiology of action. … It could be that one of these creatures believes that he is at that elegant, bibulous Oxford dinner, when in fact he is slogging his way through some primeval swamp, desperately fighting off hungry crocodiles.1

Everything we believe about evolution could be false. And this is obviously to reduce Darwinian epistemology to a reductio ad absurdum. If our theory of knowledge embraces indifferently the true and the false, so long as it is expedient, we are in deep trouble. Plantinga calls this “Darwin’s Doubt,” because it was even expressed by a worried Darwin himself, in correspondence written toward the end of his life: “With me the horrid doubt always arises whether the convictions of man’s mind, which has been developed from the mind of the lower animals, are of any value or are at all trustworthy. Would anyone trust in the convictions of a monkey’s mind, if there are any convictions in such a mind?” (As a matter of fact, Darwin immediately excused himself as a reliable authority on such philosophical questions, but Plantinga leaves this somewhat awkward point unmentioned.)

De Sousa has a two-part response to this criticism. First, he argues that our mathematical abilities cannot be the result of natural selection. “On the evolutionary scale, mathematics is part of our present rather than of our evolutionary past. It is therefore out of the question for mathematical talent as such to have been a factor in evolution by natural selection.” Then he goes on to say:

“Once mathematics had emerged into the light of day, there was still nothing to guarantee that it could prove useful outside the domains in which our practical skills had already been operating for millennia. And yet, pure mathematics notoriously finds all kinds of startling applications in the solution of technological and scientific problems that our ancestors could not possibly have conceived of, and it does so by generating theories that would have remained wholly unintelligible to them. That strongly supports the idea that mathematics can uncover aspects of the universe of which neither the usefulness nor even the existence could possibly have been manifested in the environment of our evolutionary adaptations (EEA) in which the basic functions of the brain were being shaped by natural selection. As [Eugene] Wigner has argued, this constitutes at least prima facie evidence for the conclusion that the truths of mathematics do not merely reflect projective constructions of our brains, but probably correspond to an objective reality.”

I am not sure about either of these steps. It is true that an ability for calculus was not needed in the jungle or the move out onto the plains—students of human evolution think that the key break from the chimps occurred about five million years ago when our ancestors came down from the trees and out into the open—but this is not to say that the components of reasoning abilities were not produced by selection. There are good biological reasons why humans have innate abilities at counting, working with sets, geometrical understanding, and so forth. It is true that these rather modest talents then need to be put together, but that is what education is all about.

In any case, I agree that the power of mathematics is pretty impressive. Let me correct that—incredibly impressive. And I agree it is hard to see how it works so well if it is not true. But I am not sure that this will meet Plantinga’s criticism. He argues that even if we discount the known ways that selection misleads us (I guess if he had heard of it, he would put the Wason experiment in here), it could be that selection is systematically misleading us all of the way. In a sense, his argument is a version of that used by Descartes in the Meditations—we think we are on safe ground against skepticism when we turn to mathematics, but an evil demon could be misleading us systematically about even that. You, silly person, think that 2+2=4 and that Stephen Harper has your best interests at heart, but—who knows?—a malevolent god could be deceiving you.

To which the response is the same to Plantinga as it is to Descartes: you are probably right, but that is a level of skepticism about knowledge that excites philosophers and not mature human beings. In a way, I think de Sousa is scared of regular philosophers and not prepared to endorse fully the radical position that his other arguments implicitly suggest. It is not always easy being right.

Move on now through Why Think? The central part of de Sousa’s book looks at collective thinking versus individual thinking. When is something that is rational for the individual not necessarily the most rational move for the group? One of the main things about thinking from an evolutionary perspective is that one does not necessarily expect nice, neat answers. If a good god did everything, ultimately one would expect no conflicts between individual and group goods. If evolution through natural selection does everything, such harmony is not guaranteed and hardly to be expected at all. I might say, speaking somewhat regretfully as a male interested in those sorts of things, that sexuality is one case where the individual and the group come apart. It would be better for the group of sexual organisms to have just a few fertilizing males and many nurturing females. Whatever the benefits of sexuality—and this is a much-debated question in evolutionary circles—just a few males can do the job, and in fact in most species just a few males do, since the rest get pushed to the side lines. Unfortunately, natural selection works at an individual level and so, if there is an imbalance of males, it tends toward the interests not of the group but of the parents—and it is in a parent’s interest to have male children if males are the minority sex. This prevails until equality is achieved. It will be interesting to see in China and India, countries where policies have led to a surplus of males, whether nature now reasserts itself, makes daughters more valuable and hence causes the number of females to rise.

Finally, de Sousa moves us on to irrationality. There is a nice discussion of superstition and also of why we sometimes flub even quite simple calculations. Here’s a good one. Suppose you take a test for a certain kind of cancer. The cancer is not common. It affects 0.01 percent of the population. In other words, one person in ten thousand. The test is 98 percent reliable. You get a positive reading. What are the chances that you have that cancer? I suspect most people (me!) would conclude that you are doomed. But, in fact, statistically the chances are less than half a percent. (Buy the book if you want to find out why!) In other words, we can work out the right answers, but it is not easy—and there is a good reason why it is not easy. Human reason is a faculty evolved to help us survive in certain contexts, rather than reach the truth on every occasion, and historically we have rarely been challenged to work things out at such abstract levels.

This is a great little book that should be read by many people. I would like to see de Sousa do a follow up book on morality—why do we make certain moral choices but not others? For instance, if you saw a rail cart, out of control, going down the track, about to kill ten people, and could choose to switch the points to send the cart onto a side line and kill just one person, you would probably switch the points. Now suppose you are the doctor in a ward with ten people dying for want of an organ. In walks the editor of this magazine who could be harvested to provide pieces for all ten. Would you sacrifice her? I doubt you would do it. Why? Does evolution throw some light on this paradox, for formally the situation is the same in both cases? I suspect that evolution might indeed have something to say here, and I would like to see Ronnie de Sousa act as its mouthpiece.


  1. James Sennet, editor (1998),The Analytic Theist: An Alvin Plantinga Reader (Grand Rapids, MI: Wm. B. Eerdmans Publishing).