Reading focus
Syllabus: How Does Evolution Help Explain Behavior?
Treat the catalogue of alternatives as a demand for discriminating evidence, including evidence for constraints and by-products.
Why you’re reading it. Prepare to evaluate a functional experiment without accepting either an adaptive or a nonadaptive story by default.
A question to consider. If striped plumage resembles a predator, propose an adaptive account and an alternative, then identify an observation that would distinguish them.
Why this reading
An appealing account of what a trait does can leave its origin unexplained. Gould and Lewontin challenge the habit of treating organisms as collections of independently optimized parts. Their argument makes the definition of a trait, the alternatives considered, and the evidence for selection part of the explanation.
Before you read
An adaptation, in the historical sense, is a feature shaped by selection for a function. Current utility concerns what it does now. Genetic drift is chance change in inherited variants' frequencies. Developmental and structural constraints limit the forms that can arise; a by-product can accompany change in another feature. The architectural examples are analogies, not biological experiments.
Read for
- Separate objections to defining independent traits from objections to accepting plausible stories without discriminating evidence. How would each change a research design?
- Follow the alternatives in section 5. Distinguish a correlated consequence of selection elsewhere, historical contingency among adaptive solutions, and later use of an existing feature.
Consider afterwards
- A behavior is useful today. What evidence would distinguish origin for that use from later recruitment of an older behavior?
- How could the same demand for evidence be applied to a proposed constraint or by-product explanation?
Editorial context
This is a forceful historical critique, not a demonstration that selection is unimportant or that most traits lack adaptive functions. Its alternative explanations also require tests. The authors acknowledge trade-offs but argue that invoking them can preserve an assumption of optimality without testing it. Evaluate that methodological objection separately from the accuracy of every illustrative historical claim.