Another approach, emerging more recently from the field of evolutionary psychology, objects: religion surely didn’t evolve and wasn’t consciously invented for any specific purpose or to solve any specific problem. It wasn’t the case that some budding chief got a brilliant idea one day and invented religion from scratch, foreseeing that he could more easily hold his subjects in sway if he convinced them of religious reasons to build a pyramid. Nor is it likely that a psychologically attuned hunter-gatherer, concerned that his fellow tribesmen had become too depressed by a recent death to go hunting, made up a story about the afterlife in order to console them and give them new hope. Religion instead probably arose as a by-product of some other capacities of our ancestors and of their own animal ancestors, and those capacities had unforeseen consequences and gradually acquired new functions as they developed.
To an evolutionary biologist like myself, there is no contradiction between these two different approaches to the origin of religion, in effect postulating two stages. Biological evolution itself similarly proceeds in two stages. First, variation between individuals is generated by mutations and recombinations of genes. Second, because of natural selection and sexual selection there are differences among the resulting variant individuals in how they survive, reproduce, and pass on their genes to the next generation. That is, some of those variant individuals turn out to perform functions and to solve life’s problems better than do other variant individuals. A functional problem (e.g., surviving in a colder climate) isn’t solved by an animal realizing that it needs thicker fur, nor by cold climates stimulating mutations for a thicker fur. Instead, something (in the case of biological evolution, the mechanisms of molecular genetics) creates something else (in this case, an animal with thicker or thinner fur), and some life conditions or environmental problems (in this case, cold temperatures) endow some but not others of those variant animals with a useful function. Thus, gene mutations and recombinations provide the origins of biological diversity, while natural selection and sexual selection sieve that starting material by the criterion of function.
Similarly, evolutionary psychologists assert that religion is a by-product of features of the human brain that arose for reasons other than building pyramids or comforting bereaved relatives. To an evolutionary biologist, that’s plausible and unsurprising. Evolutionary history is chock-full of by-products and mutations that were initially selected for one function and then developed further and became selected to fulfill another function. For example, creationists skeptical of the reality of evolution used to point to electric eels that electrocute their prey with 600-volt shocks, and then argued that a 600-volt eel could never have arisen from a normal no-volt eel by natural selection, because the necessary intermediate stages of low-voltage eels couldn’t electrocute any prey and wouldn’t be good for anything. In fact, it turns out that 600-volt eels evolved through changes of function, as a by-product of electric field detection and electricity generation in normal fish.
Many fish have skin sense organs sensitive to electric fields in the environment. Those fields can be either of physical origin (e.g., from ocean currents or from the mixing of waters of different salinities), or else of biological origin (from the electrical triggering of animals’ muscle contractions). Fish possessing such electric-sensitive sense organs can employ them for two functions: to detect prey, and to navigate through the environment, especially in muddy water and under nighttime conditions where eyes are of little use. The prey reveal themselves to the animals’ electric field detector by having a much higher electrical conductivity than does fresh water. That detection of environmental electric fields may be termed passive electrodetection; it does not require any specialized electricity-generating organs.
But some fish species go further and generate their own low-voltage electric fields, which let them detect objects not only by an object’s own electric field, but also by its modification of the electric field set up by the fish. Organs specialized to generate electricity evolved independently in at least six separate lineages of fish. Most electrical organs are derived from the electricity-generating membranes of muscles, but one fish species develops its electric organs from nerves. The zoologist Hans Lissmann furnished the first compelling proof of such active electrodetection, after much inconclusive speculation by others. Lissmann conditioned electric fish, by food rewards, to distinguish an electrically conducting object from a non-conducting object of identical appearance, such as a 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.