conducting metal disk versus an identical-looking non-conducting plastic or glass disk. While I was working in a Cambridge University laboratory near the building in which Lissmann was doing his studies, a friend of Lissmann told me a story illustrating the sensitivity of electrodetection by electric fishes. Lissmann noticed that a captive electric fish that he was maintaining in his laboratory got excited around the same time in the late afternoon of every weekday. He eventually realized that it was because his female technician was getting ready to go home at that hour, stepped behind a screen, and combed her hair, which set up an electric field that the fish could detect.
Low-voltage fish use their electricity-generating organs and their skin electrodetectors for improved efficiency of two different functions, both shared with the many fish possessing electrodetectors but lacking electricity-generating organs: prey detection and navigation. Low-voltage fish also use each other’s electric impulses for a third function, that of communicating with each other. Depending on the pattern of the electric impulses, which varies among species and individuals, a fish can extract information and thereby recognize the species, sex, size, and individual (strange or familiar) of fish generating the impulses. A low-voltage fish also communicates social messages to other fish of its species: in effect, it can electrically say, “This is my territory, you get out,” or “Me Tarzan, you Jane, you turn me on, it’s time for sex.”
Fish generating a few volts could not only detect prey but could also use their shocks for a fourth function: to kill small prey, like minnows. More and more volts let one kill bigger and bigger prey, until one arrives at a 600- volt eel six feet long that can stun a horse in the river. (I remember this evolutionary history all too vividly, because I started to do my Ph.D. thesis on electricity generation by electric eels. I got so absorbed in the molecular details of electricity generation that I forgot the end results, and I impulsively grabbed my first eel to start my first experiment—with a shocking outcome.) High-volt fish can also use their powerful discharges for two more functions: to defend themselves against would-be predators, by blasting the attacker; and to hunt by “electrofishing,” i.e., attracting prey to the electrically positive end of the fish (the anode), a technique also used by commercial fishermen who however have to generate electricity with batteries or generators rather than with their own bodies.
Now, let’s go back to those skeptical creationists who object that natural selection could never have produced a 600-volt eel from a normal no-volt eel, supposedly because all the necessary intermediate stages of low-volt electric organs would have been useless and wouldn’t have helped their owners survive. The answer to the creationist is that killing prey with a 600-volt shock wasn’t the original function of electric organs, but arose as a by-product of an organ initially selected for other functions. We’ve seen that electrical organs acquired six successive functions as natural selection ramped up their output from nothing to 600 volts. A no-volt fish can do passive electrodetection of prey and can navigate; a low-volt fish can perform those same two functions more efficiently, and can also electrocommunicate; and a high-volt fish can electrocute prey, defend itself, and carry out electrofishing. We shall see that human religion topped electric eels by traversing seven rather than just six functions.
The search for causal explanations
From which human attributes might religion similarly have arisen as a by-product? A plausible view is that it was a by-product of our brain’s increasingly sophisticated ability to deduce cause, agency, and intent, to anticipate dangers, and thereby to formulate causal explanations of predictive value that helped us survive. Of course animals also have brains and can thereby deduce some intent. For instance, a Barn Owl detecting a mouse by sound in complete darkness can hear the mouse’s footsteps, calculate the mouse’s direction and speed, thereby deduce the mouse’s intent to continue running in that direction at that speed, and pounce at just the correct time and place to intersect the mouse’s path and capture the mouse. But animals, even our closest relatives, have far less reasoning ability than do humans. For example, to the African monkeys known as vervet monkeys, ground-dwelling pythons are major predators. The monkeys have a special alarm call that they give at the sight of a python, and they know enough to jump up into a tree if warned by the python alarm call of another monkey nearby. Astonishingly to us, though, those smart monkeys don’t associate the sight of the python’s track in the grass with the danger that a python may be nearby. Contrast those weak reasoning abilities of monkeys with the abilities of us humans: we have been honed by natural selection for our brains to extract maximum information from trivial cues, and for our language to convey that information precisely, even at the inevitable risk of frequent wrong inferences.
For instance, we routinely attribute agency to other people besides ourselves. We understand that other people have intentions like ourselves, and that individuals vary. Hence we devote much of our daily brain activity to understanding other individual people and to monitoring signs from them (such as their facial expressions, tone of voice, and what they do or don’t say or do), in order to predict what some particular individual may do next, and to figure out how we can influence her to behave in a way that we want. We similarly attribute agency to animals: ! Kung hunters approaching a prey carcass on which lions are already feeding look at the lions’ bellies and behavior to deduce whether the lions are sated and will let themselves be driven off, or whether they are still hungry and will stand their ground. We attribute agency to ourselves: we notice that our own actions have consequences, and if we see that behaving in one way brings success and another doesn’t, we learn to repeat the action associated with success. Our brain’s ability to discover such causal explanations is the major reason for our success as a species. That’s why, by 12,000 years ago, before we had agriculture or metal or writing and were still hunter-gatherers, we already had by far the widest distribution of any mammal species, spread from the Arctic to the equator over all of the continents except Antarctica.
We keep trying out causal explanations. Some of our traditional explanations made the right predictions for reasons that later proved to be scientifically correct; some made the right predictions for the wrong reason (e.g., “avoid eating that particular fish species because of a taboo,” without understanding the role of poisonous chemicals in the fish); and some explanations made wrong predictions. For example, hunter-gatherers overgeneralize agency and extend it to other things that can move besides humans and animals, such as rivers and the sun and moon. Traditional peoples often believe those moving inanimate objects to be, or to be propelled by, living beings. They may also attribute agency to non-moving things, such as flowers, a mountain, or a rock. Today we label that as belief in the supernatural, distinct from the natural, but traditional peoples often don’t make that distinction. Instead, they come up with causal explanations whose predictive value they observe: their theory that the sun (or a god carrying the sun in his chariot) marches daily across the sky fits the observed facts. They don’t have independent knowledge of astronomy to convince them that belief in the sun as an animate agent is a supernatural error. That isn’t silly thinking on their part: it’s a logical extension of their thinking about undoubtedly natural things.
Thus, one form in which our search for causal explanations overgeneralizes and leads straightforwardly to what today we would term supernatural beliefs consists of attributing agency to plants and non-living things. Another form is our search for consequences of our own behavior. A farmer wonders what he did differently this time to cause a formerly high-yielding field to have a poor yield this year, and Kaulong hunters wonder what a particular hunter did to cause him to fall into a hidden sinkhole in the forest. Like other traditional peoples, the farmers and the hunters rack their brains for explanations. Some of their explanations we now know to be scientifically correct, while others we now consider to be unscientific taboos. For instance, Andean peasant farmers who don’t understand coefficients of variation nevertheless scatter their crops among 8 to 22 fields (Chapter 8); they may traditionally have prayed to the rain gods; and Kaulong hunters are careful not to call out the names of cave bats while hunting bats in areas with sinkholes. We have now become convinced that field scattering is a scientifically valid method to ensure yields above some minimum value, and that prayers to rain gods and taboos on calling bat names are scientifically invalid religious superstitions, but that’s the wisdom of hindsight. To the farmers and hunters themselves, there isn’t a distinction between valid science and religious superstition.
Another arena for over-pursuit of causal explanations is theories of illness. If someone gets sick, the victim and her friends and relatives search for an explanation of the illness just as they would for any other important happening. Was it due to something that the sick person did (e.g., drinking from a certain water source), or neglected to do (e.g., washing her hands before eating, or asking a spirit for help)? Was it because of something that someone else did (e.g., another sick person sneezing on her, or a sorcerer working magic on her)? Like traditional people, we First World citizens in the era of scientific medicine continue to seek satisfying explanations for illness. We have come to believe that drinking from a certain water source or not washing one’s hands before
