If you’re an economist, you know about Jan Tinbergen, who shared the first Nobel Prize in Economics with Ragnar Frisch in 1969 for his work on dynamic models of economic processes. If you’re an evolutionist, you know about the other Tinbergen, Jan’s younger brother Niko, who shared the Nobel Prize in Medicine with Konrad Lorenz and Karl von Frisch in 1973 for his foundational work on ethology, the study of animal behavior.
Niko wrote an elegant paper in 1963 titled “On the Aims and Methods of Ethology” that summarizes, in the form of four questions, why evolutionary theory is so good at integrating across disciplines. Tinbergen’s four questions go a long way toward answering the question “What’s evolution got to do with it?”
1) What is the function of the trait, or why does it otherwise exist compared to the many traits that could exist in the lineage? The process of variation and selection winnows a small subset of traits that adapt organisms to their environments from a much larger set of traits that could equally exist but do not because they were not selected. Evolutionists call this ultimate causation. It provides a powerful (but not infallible) way of inferring the properties of organisms knowing only a little bit about the environmental context. For example, we can confidently predict that desert creatures are likely to be sandy colored to avoid being detected by their predators and prey. We can make this prediction for all desert-dwelling creatures, without knowing anything about their genes or physical makeup.
Although this example is simple, adaptationist thinking is full of complexities and pitfalls. Not all traits are adaptive; they can be a product of drift, a byproduct of other traits, or adaptive in the past but not the present. When they are adaptive, they might benefit genes, individuals or groups. They might be a product of sexual rather than natural selection. What counts as adaptive in the evolutionary sense of the word can be perversely maladaptive in the everyday sense of the word. Species can even evolve themselves to extinction. Thus, although the answer to Tinbergen’s first question can be a no-brainer, it can also require a sophisticated understanding of evolutionary theory.
2) What is the phylogeny, or evolutionary history of the trait? Answering this question provides information that was not required to answer the first question. A marsupial’s pouch and placental mammal’s womb have the same function (to develop offspring) but are very different from each other, based on the fact that marsupials and mammals evolved on different continents. Evolution is a historical process and seldom takes exactly the same path twice. A trait will not be fully understood until its particular evolutionary trajectory is known.
3) What is the mechanism of the trait? Regardless its function or history, it also has a physical basis that must be understood in mechanistic terms. Evolutionists call this proximate causation. The functional answer to why flowers bloom in spring is because that’s the best time to bloom for the survival and reproduction of the plant. The mechanistic answer can be completely different, such as a physiological response to day length.
4) How did the trait develop? Organisms have histories in addition to lineages and the development of traits usually reflects a complex interaction between the organism and the environment, even when the outcome is highly invariant, such as the development of the eye.
Each question can be answered independently to a degree but they are best answered in combination. This is the kind of integration that is far more advanced for the biological sciences than for human-related subjects. Even the biological sciences are still a work in progress. It is common for evolutionists to reason on the basis of ultimate causation without paying much attention to proximate causation. It is even more common for biologists who concentrate on proximate causation, such as molecular biologists, to ignore ultimate causation. Phylogenies are often constructed without reference to the selection pressures that partially brought them about. And the so-called modern synthesis that formed in the 1940’s largely ignored development, which is why “evo-devo” became a new field of inquiry in the 1980’s. Research programs that provide answers to all four questions are awesome in their scope and explanatory power, such as Richard Lenski’s research on experimental evolution in microbes. Most biologists would agree that this is the ideal to strive for, even when it is difficult to achieve for particular study systems.
For decades, we have been fancied as set apart from the rest of life by our capacity for cultural change, as if this lifts us outside the orbit of evolution. Once we realize that this capacity is a product of genetic evolution and itself an evolutionary process, the need for Tinbergen’s four questions becomes doubly needed–to explain both the capacity and the specific products of cultural evolution.
The ideal of answering all four questions in an integrated fashion forces the evolutionist to integrate knowledge across disciplines. It is impossible to study human psychology, for example, without consulting anthropology and paleo-anthropology. In the recent EI/NESCent workshop on integrating economics and evolution, the participants represented the fields of anthropology, economics, history, political science, psychology, neurobiology, and theoretical biology. The conversation easily shifted from one discipline to another, because we were all accustomed to thinking about Tinbergen’s four questions in an integrated fashion. Contrast this with the encapsulated nature of economics as a discipline, which isolates it from other human-related disciplines, not to speak of the biological sciences. The workshop participants were trying to formulate an answer to the question “What’s evolution got to do with it?”, but the fact that we were in the same room and capable of talking with each other provided part of the answer.
Who would have thought that the other Tinbergen would have even more to say about economics than his older brother?