The concept of byproducts has become a very popular mechanism that some anthropologists, psychologists, and other academics have embraced as a means to explain the purpose and origin of religion. These include some of the most well-known evolutionary biologists such as Steven Pinker and Richard Dawkins. But what is a biological byproduct? We know what a byproduct is in chemical reactions—carbon dioxide is a waste byproduct of anaerobic fermentation as is alcohol (although for people, alcohol production is the goal). Carbon dioxide is also a waste byproduct of animal metabolism and respiration. But what is a byproduct when it comes to actual genotypic or phenotypic biological traits? Where else do we find examples of it, and how do we determine if something is a biological byproduct?

The justification for applying byproduct ideas to biology and ultimately religion was popularized in a 1979 paper by Harvard evolutionary biologists Richard Lewontin and the late Steven Jay Gould. Called The Spandrels of San Marcos, the article criticized biologists for excessively invoking adaptations to explain traits. The authors purported that not all biological characteristics were evolved adaptations or arose due to natural or sexual selection, but rather were due to either random factors such as gene drift or are byproducts of other adaptive characteristics. Gould and Lewontin introduced the architectural concept of spandrels, a non-functional side-effect of arches and column construction. They cited these triangular spaces formed by the intersection of two rounded arches as the germane example on which to base their argument against the overuse of adaptation and selection theory. They didn’t however provide substantial biological examples of byproducts and claimed they were doing their readers a favor by avoiding biological examples. “We deliberately chose non-biological examples in a sequence running from remote to more familiar: architecture to anthropology. We did this because the primacy of architectural constraint and the epiphenomenal nature of adaptation are not obscured by our biological prejudices.” (p 584) Really!? Such a statement seems immediately and oddly disingenuous. Would it have been because they were unable to identify and describe convincing biological examples of non-adaptive features? Instead of delving into examples of biological byproducts—they are evolutionary biologists after all—Gould and Lewontin proceed to criticize the “adaptationist programme” and show how biologists miscategorize traits as adaptations when they are not. They also describe legitimate non-adaptive forces like gene drift, the well-studied randomness that some traits exhibit in populations. What they assiduously avoid is examining the biology of byproducts.

In his book The Panda’s Thumb, Gould explains the derivation of this appendage that is used by the panda to strip away bamboo leaves so it can eat the shoots. The panda’s thumb is a bone called the radial sesamoid, which in other animals is normally a much smaller bone in the wrist. The sesamoid bone in pandas evolved to be very large. This is an instance of how a structure designed by natural selection for one purpose, in this case to support the wrist, can evolve adaptively to perform a different function. Gould does not claim that this is an example of a byproduct. Instead he explains, “The panda’s true thumb is committed to another role, too specialized for a different function to become an opposable, manipulating digit. So the panda must use parts on hand and settle for an enlarged wrist bone and a somewhat clumsy, but quite workable, solution...But it does its job and excites our imagination all the more because it builds on such improbable foundations.” He uses the same “panda’s thumb” logic in a 1997 follow-up to the original spandrel article called The Exaptive Excellence of Spandrels as a Term and Prototype. There Gould continues his critique of what he saw as the overly simplistic use of adaptation theories by calling them “just-so” stories based on Rudyard Kipling’s writings that adopt a mythological style for explaining the origins of animal characteristics. Gould gives the example of the evolution of the bird’s wing, which like the panda’s thumb, arose for one reason and evolved into a different function. “If the earliest stages in the evolution of a wing, for example, offer no conceivable benefit in flight, then these incipient structures must have performed some other primary function and been coopted later (and at more elaborate form) for aerodynamic benefit. Darwin speaks of ‘the highly important fact that an organ originally constructed for one purpose...may be converted into one for a widely different purpose’.” Note that Gould says the original development of the wing did not serve a flying function, but must have served some other primary function. He doesn’t, however, indicate if this pre-flying structure is adaptively evolved.

What follows next can only be categorized as a duplicitous bait and switch. He says, “This principle of quirky and unpredictable functional shift underlies much of evolution’s contingency but does not alter or broaden the adaptationist paradigm because structures still arise by selection, and for utility—albeit for a different function than homologs in modern descendants now perform.” So far, so good. Bird wings and panda thumbs can evolve for one purpose but become adapted for something else. Then he pulls the switcheroo. “The principle of spandrels provides a more radical version of cooptation ‘for a widely different purpose’ because the exapted structure originated as a byproduct and not as an explicit adaptation at all. Therefore, structures that may later become crucial to the fitness of large and successful clades [a group of related species] may arise nonadaptively (whatever their subsequent, coopted utility)—and the principle of adaptation cannot therefore enjoy the near ubiquity that strict Darwinians wish to impute.” (1997 p 10754) Where did this come from? Suddenly they suggest a characteristic that eventually evolved into a wing was not initially adaptive. On what basis? Gould doesn’t provide a specific example of a byproduct; he only proposes that a bird’s wing, which eventually evolved to enable flying, may have arisen from a non-adaptive byproduct. He doesn’t explain any specifics of how or why a pre-wing structure is a byproduct, only that it could be. He’s trying to pull a fast one and throwing out a contrived, completely unsubstantiated notion to make his case for byproduct theory and hoping that no one will question or challenge his lack of evidence and logic to make his case.

A scientist is obligated to provide empirical data to support his claims, but Gould doesn’t; he only has a hypothetical idea. He “chose non-biological examples” to make his case for byproducts and spandrels because he had no biology to show. In fact it is the theory of biological byproducts that is a “just so” story fabricated for the purpose of achieving an ideological agenda, which is to undermine the significance of evolutionary theory to Homo sapiens. Like many others, Gould and Lewontin believe it is important to show that human cognitive plasticity is virtually unlimited; that people can become whatever they want to become. It’s a return to the behaviorist argument of the first half of the twentieth century when B.F. Skinner asserted that humans had no instincts and that nurture was everything. Human personality developed solely from upbringing. Gould famously said, “natural selection has almost become irrelevant in human evolution. There’s been no biological change in humans in 40,000 or 50,000 years.” (Gould 2000) Evolution, he claimed, ceased to have an impact on humanity. Not only is this claim completely erroneous and mistaken, but it misrepresents the essence of evolution, which is absolutely shocking for a scientist of Gould’s stature. Gould attempts to form a theory that lifts the force of evolution off our species. If people were not subject to selection, than our species becomes freed from the shackles of their biology. It’s one thing to claim this in the sociological or political sphere, but it’s quite another to declaim this in the scientific community where experimentation is required to support the hypothesis. Since the discovery of the structure of DNA the evidence has accumulated that, if anything, the genetic contribution to the human animal has been underestimated.

Byproduct theory is a way to remove adaptiveness as a requisite consideration for human traits like religion, but what byproduct theorists don’t do is provide a strict definition of a biological byproduct or what criteria or characteristics contribute to a byproduct. Nor have there been papers in the scientific literature that undertake that effort. This is not to say that there aren’t many articles in the science journals debating the relative contribution of adaptive and non-adaptive evolutionary forces, but byproduct theory has no basis in science.

The icing on Gould’s agenda arrives on the last page of The Exaptive Excellence article. “Organs of extreme complexity must include capacities for cooptation that can exceed, or even overwhelm, the primary adaptation. The chief example in biology may be a unique feature of only one species, but we obviously (and properly) care for legitimate reasons of parochial concern. The human brain may have reached its current size by ordinary adaptive processes keyed to specific benefits of more complex mentalities for our hunter-gatherer ancestors on the African savannahs. But the implicit spandrels in an organ of such complexity must exceed the overt functional reasons for its origin.” (1997 p. 10755) When he says humans are the chief or sole example of a unique feature, alarms go off. Any time Homo sapiens are the beneficiaries of special consideration, at least in biology, suspicion is aroused. It smells of geocentrism; we are the center of the universe. Galileo and Copernicus put that to bed a while ago, but it continues to rear its head in different forms, usually in religion and politics. Hmm, politics and religion. At least if a case for byproduct theory is to be made, it needs to undergo the scrutiny of peer-reviewed debate in the scholarly literature unlinked to human expressions like religion. That certainly hasn’t happened.

Reaching into classic Darwinian theory, biologists work hard to assign adaptive mechanisms to characteristics (phenotypes). It bothers Gould and Lewontin that when one proposed adaptation for a trait is disproved to be adaptive after all, the biologists continue look for a different explanatory adaptation. What Gould and Lewontin want is for biologists to consider non-adaptive reasons for traits, but even if the biologists are wrong when advancing adaptive explanations a second and third time, that doesn’t mean that they should stop looking for adaptations to explain organisms’ traits. “The problem,” Krebs and Davies say, “with non-adaptive explanations is that they are hypotheses of the last resort. Further scientific enquiry is stifled. Maybe there is an adaptive explanation for the difference but we just haven’t discovered it yet.” (p. 31)

Despite the incompleteness of byproduct theory, it has become wildly popular among many academics as a means to explain some of the more mysterious human behaviors. In his book How the Mind Works, Steven Pinker combines evolutionary biology with cognitive science to reveal the inner workings of the human brain. After 500 quality pages of deconstructing the mind within an evolutionary framework, Pinker confesses, “I will conclude by arguing that some of the activities we consider most profound are nonadaptive byproducts.” (p. 525) By non-adaptive byproducts Pinker refers to arts and religion; that these ubiquitous behaviors do not contribute any evolutionary benefit and do not fall under the evolutionary rubric. For Pinker arts and religion are not adaptive because they don’t exhibit all characteristics of an adaptive behavior. They must be universal, complex, reliably developing, well-engineered, and reproduction-promoting, he says. Arts and religion are certainly complex and universal. The evidence exists that they are well-engineered and reliably developing. The only obvious deficiency from adding them to the biologically adaptive club is no one has adequately accounted for how they are reproduction-promoting. Pinker rightly points out that it is wrong to invent functions for activities that lack evolutionary design just “because we want to ennoble them with the imprimatur of biological adaptiveness,” (p. 525) which is one of the arguments Gould and Lewontin made. It is equally wrong to invent hyperbole like byproduct theory.

Pinker is far from alone in jumping to the hypothesis of last resort. The scion of evolutionary biology, Richard Dawkins, grasps at byproduct theory in his attack on religion in his book The God Delusion. See my short essay on Dawkins’s faith-based religious beliefs to see how his religion as byproduct arguments are illogical, contradictory, and veer from evolutionary theory rather than embracing it.

A contingent of academics who dedicate their careers to studying the origins and function of religion has embraced byproduct theory. Some of the notables are Scott Atran, Pascal Boyer, Justin Barrett, and Lee Kirkpatrick. Pyysïäinen and Hauser, also byproduct endorsers, provide a representative definition. “Religious beliefs are a byproduct of evolved cognitive mechanisms. These cognitive mechanisms enable us to reason about the intentional states of others and to recursively embed intentional states within other intentional states, and make it possible for us to think what others think, including absent or even dead persons, fictional characters, and also supernatural agents.“ (p 105)

It’s quite remarkable, almost even amazing, that religion as byproduct theory has become prevalent in academic circles. One issue already discussed is that no rigorous evaluation or analysis exists stating what makes religion or anything else a byproduct. At the very least there needs to be a small library of journal articles debating this very issue just as there already is for whether religion is a byproduct or adaptation and whether its primary function is group cohesion, the agency detection device, to answer the existential mysteries, or something else. Nothing like that exists for byproduct theory, or if it does, I would love to see it.

The second issue with byproduct theory of religion is ideological in nature just as it was for Gould and Lewontin. Because a cogent and widely accepted theory of religion remains elusive, byproduct theory is utilized as a big bin that you throw religion into when you don’t have a more satisfactory, evolutionary-based solution. It’s more about attaining intellectual goals and is not unlike self-serving religious diatribes in which chest-pounding clergy or politicians invoke God’s blessing to claim divine right and moral eminence. Its more important to divine a solution than worry about the veracity of its assumptions.

On top of that, and in what feels like a travesty of justice, the academic papers that promote adaptationist arguments for religion and against byproduct proponents are forced to take a defensive position. Instead of putting the burden of proof on those who promote byproduct theory, adaptationists are forced to defend adaptationism, a principle component of 150-year-old Darwinian evolutionary theory. It isn’t from lack of trying. In Adaptation, Evolution, and Religion, Stephen Sanderson says, “Few evolutionary biologists have accepted Gould and Lewontin’s strong conclusions (although they often concede that their arguments can serve as useful cautions against uncritical acceptance of adaptationism). Be that as it may, Kirkpatrick, despite otherwise very cogent arguments, seems to be endorsing the kind of position advocated by Gould and Lewontin when he contends that byproduct theory rather than adaptationism should be the default assumption in the evolutionary study of religion. I am at a loss to understand this claim, which has almost no warrant in the entire history of evolutionary biology or evolutionary psychology.” (p. 147) Proponents of religion as an adaptation are hampered because of inadequate models to show how religion improves fitness or evolutionary success, but byproduct theorists are similarly challenged. No theory of religion, whether byproduct or adaptationist, has achieved anything close to a consensus that explains religious phenomena.

Gould and Lewontin do a lot of huffing and puffing to make spandrels into a legitimate biological construct, but they mostly discuss architecture rather than biology. They only provide a few paltry or misleading examples and leave undescribed what defines a biological byproduct and unanswered what criteria must be met for a form to be categorized as a byproduct. It’s truly bizarre that byproduct theory and the byproduct of religion school have gotten away with trotting out this theory for so long. Byproduct theory is like the emperor’s new clothes. Somehow its proponents have made themselves believe in it’s reality and go parading it around, except there isn’t anything there. The consequence of this should undermine the byproduct theories of religion, but despite this, the religion as byproduct school is unconcerned, unabashed, or unaware of this serious shortcoming, or all of the above. The majority of origin of religion researchers promote a byproduct explanation of religion despite byproduct theory being built on a house of cards. It is ultimately a “just so” story made up to fulfill a pre-determined agenda. For those who want to defend the byproduct theories of religion, by all means, define what a byproduct is, establish the criteria to identify a byproduct, and describe the phenomenon of biological byproducts in non-human animals. Then, once that’s filtered through the peer reviewers, slide it over to the human condition. Until that time, however, it would best be left buried deep in a museum warehouse gathering dust.

Sanderson, Stephen K. "Adaptation, Evolution, and Religion" Religion 38 (2008) 141-156