[4] The most obvious justification for an adaptationist perspective is the belief that traits are, in fact, always adaptations built by natural selection for their functional role.
Although adaptationism has always existed— the view that the features of organisms are wonderfully adapted predates evolutionary thinking— and was sometimes criticized for its "Panglossian" excesses (e.g., by Bateson or Haldane), concerns about the role of adaptationism in scientific research did not become a major issue of debate until evolutionary biologists Stephen Jay Gould and Richard Lewontin penned a famous critique, "The Spandrels of San Marco and the Panglossian Paradigm".
This critique provoked defenses by Mayr,[2] Reeve and Sherman [3] and others, who argued that the adaptationist research program was unquestionably highly successful, and that the causal and methodological basis for considering alternatives was weak.
The "Spandrels paper" (as it came to be known) also added fuel to the emergence of an alternative "evo-devo" agenda focused on developmental "constraints" [7] Today, molecular evolutionists often cite neutral evolution as the null hypothesis in evolutionary studies, i.e., offering a direct contrast to the adaptationist approach.
Richard Dawkins noted in The Blind Watchmaker that evolution, an impersonal process, produces organisms that give the appearance of having been designed for a purpose.
Reverse engineering can, in particular, help explain cognitive biases as adaptive solutions that assist individuals in decision-making when considering constraints such as the cost of processing information.
This approach is valuable in understanding how seemingly irrational behaviors may, in fact, be optimal given the environmental and informational limitations under which human cognition operates.
When organisms diverge from a common ancestor and inherit certain characteristics which become modified by natural selection of mutant phenotypes, it is as if some traits are locked in place and are unable to change in certain ways.
In his book, Why We Get Sick, Randolph Nesse uses the "blind spot" in the vertebrate eye (caused by the nerve fibers running through the retina) as an example of this.
In early vertebrate evolution, sharks, skates, and rays (collectively Chondrichthyes), the cranial nerves run from the part of the brain that interprets sensory information, and radiate out towards the organs that produce those sensations.
Structuralist critics (most notably Richard Lewontin and Stephen Jay Gould in their "spandrel" paper[15]) contend that the adaptationists have overemphasized the power of natural selection to shape individual traits to an evolutionary optimum.
Adaptationist researchers respond by asserting that they, too, follow George Williams' depiction of adaptation as an "onerous concept" that should only be applied in light of strong evidence.
[18][19] A similar term, teleonomy, grew out of cybernetics and self-organising systems and was used by biologists of the 1960s such as Ernst Mayr and George C. Williams as a less loaded alternative.