How to Study Adaptation (and Why To Do It That Way)

Abstract

Some adaptationist explanations are regarded as maximally solid and others fanciful just-so stories. Just-so stories are explanations based on very little evidence. Lack of evidence leads to circular-sounding reasoning: "this trait was shaped by selection in unseen ancestral populations and this selection must have occurred because the trait is present." Well-supported adaptationist explanations include evidence that is not only abundant but selected from comparative, populational, and optimality perspectives, the three adaptationist subdisciplines. Each subdiscipline obtains its broad relevance in evolutionary biology via assumptions that can only be tested with the methods of the other subdisciplines. However, even in the best-supported explanations, assumptions regarding variation, heritability, and fitness in unseen ancestral populations are always present. These assumptions are accepted given how well they would explain the data if they were true. This means that some degree of "circularity" is present in all evolutionary explanations. Evolutionary explanation corresponds not to a deductive structure, as biologists usually assert, but instead to ones such as abduction or induction. With these structures in mind, we show the way to a healthier view of "circularity" in evolutionary biology, and why integration across the comparative, populational, and optimality approaches is necessary.

Spandrels and trait delimitation: No such thing as “architectural constraint”

“…This is a crucial consideration because countless human traits are unique to our species, meaning that standard comparative methods, which require variation in a trait across multiple species, aren't available (Olson & Arroyo-Santos, 2015). This is a crucial consideration because countless human traits are unique to our species, meaning that standard comparative methods, which require variation in a trait across multiple species, aren't available (Olson & Arroyo-Santos, 2015).…”

“…This is a crucial consideration because countless human traits are unique to our species, meaning that standard comparative methods, which require variation in a trait across multiple species, aren't available (Olson & Arroyo-Santos, 2015). Many other tools of adaptationist evolutionary biology are also unavailable for studies in humans, such as selective breeding, directed mutagenensis, or surgical alteration to create variation, so it is often hard to amass much of the key evidence that evolutionary biologists use to distinguish between alternative explanations in non-human systems (Olson, 2012;Olson & Arroyo-Santos, 2015;Pavličev & Wagner, 2016). It is thus understandable that competing alternative explanations for the presence of human traits should generate persistent debate (Forber, 2009).…”

Range‐constrained co‐occurrence simulation reveals little niche partitioning among rock‐dwelling Montenegrina land snails (Gastropoda: Clausiliidae)

“…In allopatry, habitat descriptors and other environmental factors might be used to describe niches (McCormack, Zellmer, & Knowles, 2010). But even if habitat and climate are well-characterized, they provide little clue about the niche itself because similar habitat preferences of sister taxa cannot be seen as insurmountable evidence for their niche overlap, nor can slight differences in habitat preferences be taken as proof of niche differences (Olson & Arroyo-Santos, 2015;Sober on, 2007). When Gittenberger (1991Gittenberger ( , 2004 considered the rock-dwelling gastropods (e.g.…”

Nearly 200 years of sustained selection have not overcome the leaf area–stem size relationship in the poinsettia

“…Presumably this metabolic proportionality drives the generally strong leaf area–stem size relationship (Olson, Aguirre‐Hernández, & Rosell, 2009). Stated in terms of developmental potential, the space that the leaf area–stem size relationship describes can be thought of as having three areas (see Olson, 2012; Olson & Arroyo‐Santos, 2015). The first is the leaf area–stem size scaling line that most plants fall along, which shows that plants with greater stem size have predictably higher leaf area.…”