Breaking the Spell: Religion as a Natural Phenomenon

But isn’t there an unjustified asymmetry here, with me refusing to defend my anticreationism here and now, while sending the biblical inerrantist off for not playing by the rules of rational discussion? No, because I have directed everyone to the literature that defends the dismissal of creationism against all objections, whereas the inerrantist is refusing to take on even that obligation. To be symmetrical, the inerrantist should encourage me to consult the literature, if it exists, that purports to demonstrate, against all objections, that the Bible is indeed the Word of God and that it rules out evolution. I haven’t yet been directed to any such literature, and haven’t found it on any Web site, but if it exists, it would indeed warrant consideration as a topic for another day and another project—just like creationism and its critics. Those readers who remain will not demand any further consideration by me of creationism and its variants, since I have told them where to find the answers I endorse, for better or for worse. End of Digression.

Lawyers have a stock Latin phrase, cui bono?, which means “Who benefits from this?,” a question that is even more central in evolutionary biology than in the law (Dennett, 1995b). Any phenomenon in the living world that apparently exceeds the functional cries out for explanation. The suspicion is always that we must be missing something, since a gratuitous outlay is, in a word, uneconomical, and as the economists are forever reminding us, there is no such thing as a free lunch. We don’t marvel at an animal doggedly grubbing in the earth with its nose, for we figure it is seeking its food, but if it regularly interrupts its rooting with somersaults, we want to know why. Since accidents do happen, it is always possible that some feature of a living thing that appears to be a pointless excess is just as pointless as it appears (rather than a deep and baffling ploy in some game we don’t understand). But evolution is remarkably efficient at sweeping pointless accidents off the scene, so if we find a persistent pattern of expensive equipment or activity, we can be quite sure that something benefits from it in the only stocktaking that evolution honors: differential reproduction. We should cast our nets widely when hunting for the beneficiaries, since they are often elusive. Suppose you find rats that extravagantly risk their lives in the presence of cats, and ask the cui bono? question. What good accrues to these rats from this foolhardy behavior? Are they showing off to impress potential mates, or does their extravagant behavior somehow improve their access to good food sources? Conceivably, but probably you are looking in the wrong place for the beneficiary. Like the lancet fluke that has taken up residence in the strenuous ant with which I began this book, there is a parasite, Toxoplasma gondii, that can live in many mammals but needs to get into a cat’s stomach to reproduce, and when it infects rats, it has the useful property of interfering with their nervous systems and making them hyperactive and relatively fearless—and hence much more likely to be eaten by any cat in the vicinity! Cui bono? The benefit is to the fitness—the reproductive success—of Toxoplasma gondii, not the rats it infects (Zimmer, 2000).

Every bargain in nature has its rationale, free-floating unless it happens to be a bargain devised by human bargainers, the only rationale-representers yet to have evolved on the planet. But a rationale can become obsolete. As the opportunities and perils in the environment change, a good bargain can lapse. It takes time for evolution to “recognize” this. Our sweet tooth is a good example. Like the coyotes, our hunter-gatherer ancestors lived on very tight energy budgets, and had to avail themselves of every practical opportunity to store away calories for emergency use. A practically insatiable appetite for sweets made good sense then. Now that we have developed methods for creating a superabundance of sugar, that insatiability has become a serious design flaw. Recognizing the evolutionary source of this glitch helps us figure out how to deal with it. Our sweet tooth is not just an accident or a pointless bug in an otherwise excellent system; it was designed to do the work it does, and if we underestimate its resourcefulness, its resistance to perturbation and suppression, our efforts to cope with it are apt to be counterproductive. There is a reason why we love sugar, and it is—or used to be—a very good reason. We may find other superannuated loves that need our attention.

I mentioned music in the previous chapter, and we will eventually turn to a more detailed examination of its possible evolutionary sources, but I want to warm up first on some easier things we love. What about alcohol? What about money? What about sex? Sex presents some of the most interesting and challenging problems in evolutionary theory, because, on the face of it, sexual reproduction is a bad bargain indeed. Forget—for the moment—about our human kind of sex (sexy sex), and consider the most basic varieties of sexual reproduction in the living world: the sexual reproduction of almost all multicellular life-forms, from insects and clams to apple trees, and even many single-celled organisms. The great evolutionary biologist François Jacob once quipped that the dream of every cell is to become two cells. Every time this fission happens, a complete copy of the cell’s genome is copied into the offspring. The parent clones itself, in other words; the resulting organism shares 100 percent of its genes. If you can make perfect genetic copies of yourself, why would you go to the expense of reproducing sexually, which involves not just finding a mate but, much more important, passing on only half of your genes to your offspring?⁴ This 50 percent reduction (from the gene’s point of view) is known as the cost of meiosis (the kind of fission that occurs in sex cells, to distinguish it from the cloning fission of mitosis). Something must pay for this cost, and it must pay on delivery, not at some future date, since evolution lacks foresight and cannot approve bargains on the speculative basis of eventual return at some distant time.

Sexual reproduction is thus a costly investment that has to pay for itself in the short run. The details of theory and experiment on this topic are fascinating (see, e.g., Maynard Smith, 1978; Ridley, 1993), but for our purposes a few highlights from the currently front-running theory are most instructive: sex (in vertebrates like us, at least) pays for itself by making our offspring relatively inscrutable to the parasites we endow them with from birth. Parasites have short lifespans compared with their hosts, and typically reproduce many times during their host’s lifetime. Mammals, for instance, are hosts to trillions of parasites. (Yes, right now, no matter how healthy and clean you are, there are trillions of parasites of thousands of different species inhabiting your gut, your blood, your skin, your hair, your mouth, and every other part of your body. They have been rapidly evolving to survive against the onslaught of your defenses since the day you were born.) Before a female can mature to reproductive age, her parasites evolve to fit her better than any glove. (Meanwhile, her immune system evolves to combat them, a standoff—if she is healthy—in an ongoing arms race.) If she gave birth to a clone, her parasites would leap to it and find themselves at home from the outset. They would be already optimized to their new surroundings. If instead she uses sexual reproduction to endow her offspring with a mixed set of genes (half from her mate), many of these genes—or, more directly, their products, in the offspring’s internal defenses—will be alien or cryptic to the ship-jumping parasites. Instead of home sweet home, the parasites will find themselves in terra incognita. This gives the offspring a big head start in the arms race.