Recent decades have witnessed a dawning awareness that many diseases are caused by a mismatch between our immune systems and our modern environments. A mini-lesson on adaptive phenotypic plasticity will help to set the stage. Consider a snail species that lives in water bodies that might or might not be inhabited by crayfish. Thin shells are optimal in the absence of crayfish but thick shells are optimal in their presence. Many snail species have evolved the ability to produce either shell type along with sensitivity to environmental cues that reliably indicate the presence or absence of crayfish. The cues are often chemical, and a thick shell can be induced merely by adding water that has been inhabited by crayfish.
Now suppose that the environment of the snail species becomes polluted with a substance that mimics the scent of the crayfish. The snail will inappropriately develop thick shells in the absence of crayfish and subsequent evolution must take place for it to behave adaptively again; for example, by becoming sensitive to predator cues that are not mimicked by the pollutant. Alternatively, humans can intervene; for example, by eliminating the pollutant.
In this fashion, species that have evolved to alter their phenotypes in response to their environment are rigidly flexible, a phrase that seems like a contradiction of terms but makes perfect sense, like a Zen koan, from the right perspective. Species are adaptively flexible in responding to patterns of environmental variation that existed in the past for a long enough period for genetic evolution to produce the appropriate phenotypic response. But they are rigidly maladaptive with respect to new patterns of environmental variation.
The vertebrate immune system is amazingly flexible at fighting diseases, especially its ability to produce and select antibodies that constitutes an evolutionary process in its own right. Nevertheless, it can be dumbfounded by elements of its environment that did not exist in the past, no less than the snail species. As an example, for hundreds of millions of years, the immune system has evolved in the presence of a diverse ecosystem of microbes, worms, and other species inside our guts and on the surface of our skin. Our fellow travelers weren’t always good for us, but they were always there. For the first time in our evolutionary history, it has been possible to cleanse ourselves of these species. Conventional medical wisdom treats this as an unambiguous blessing; germs are bad and the fewer the better. The idea that excessively hygienic environments might trigger immune system dysfunction wasn’t proposed until the late 20th century. Successful interventions will require a sophisticated knowledge of the immune system in relation to past and present environments.
I would like to propose a cultural system dysfunction hypothesis that is comparable to the immune system dysfunction hypothesis. To begin, it is necessary to think about the human capacity for cultural change as a complex adaptation that evolved by genetic evolution, like the vertebrate immune system. Both are massively modular, as imagined for the human mind by evolutionary psychologists, but also have an open-ended capacity to adapt to current environments, as imagined for the human mind by the behaviorist and social constructivist traditions. Reconciling the apparent paradox of human mentality as both elaborately innate and elaborately open-ended is the subject of a target article titled “Evolving the Future: Toward a Science of Intentional Change” by myself and three distinguished behavioral scientists, Steven C. Hayes, Anthony Biglan, and Dennis Embry, which is forthcoming in the academic journal Behavioral and Brain Sciences and has a section titled “Learning from the Immune System about Evolutionary Psychology”.
One thing that we can say with reasonable certainty about human cultural systems is that they evolved in the context of small-scale social interactions. It is at this scale that we are adapted to compare behaviors and adopt those that appear most useful; to be biased toward adopting the most common behaviors or those performed by the most prestigious individuals; and to blindly copy behaviors with high fidelity under ritualistic circumstances. These are some of the “modules” that have been postulated that enable human populations to adapt to their environments more quickly than by the process of genetic evolution. They function well in the context of small-scale social interactions, but they can easily malfunction in large-scale social environments.
Our current cultural systems are a product of multilevel cultural evolution operating over the course of human history, as Peter Turchin and others have established so well with their research. What constitutes a new pattern of environmental variation in contrast to an older pattern is complicated when both genetic and cultural evolution must be taken into account. Nevertheless, rapid changes in the human social environment, especially with the advent of globalization and electronic communication, leave plenty of room for mismatches even with respect to cultural evolution.
One reason that I am starting to think about the cultural systems dysfunction hypothesis is because of my experience as president of the Evolution Institute, which formulates public policy from an evolutionary perspective. I have learned that the world of public policy is full of programs and practices that work but don’t spread, as I recount for one of my own programs here. The comparison and adoption of best practices that takes place spontaneously at a small social scale breaks down at a larger scale. Unless a system for identifying and replicating best practices is implemented at a larger scale, there is no hope for adapting to our current environments.
The hypothesis that some of our social dysfunctions are comparable to autoimmune disease is rich with possibilities. Developing the hypothesis will require a sophisticated knowledge of cultural systems in relation to past and present environments. Our current knowledge of cultural systems is far more rudimentary than our knowledge of the immune system. It would be hard to imagine a more important priority for basic and applied scientific research.