The Spandrels Paper

Origins and Argument

Published in 1979, Stephen Jay Gould and Richard Lewontin's "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme" challenged the prevailing tendency within evolutionary biology to explain every observable trait as a specific adaptation shaped by natural selection. The paper's central argument was that many features of organisms, rather than being direct adaptations, might instead be non-adaptive byproducts of other evolutionary processes or architectural constraints.

The paper opens with an extended metaphor drawn from architecture: the spandrels of San Marco Cathedral in Venice. Spandrels are the roughly triangular spaces formed between the tops of adjacent arches and the ceiling above them. While often elaborately decorated with mosaics or frescoes, Gould and Lewontin argued that these spaces are not designed for the artwork; rather, they are inevitable structural byproducts of placing a dome on rounded arches. The artists then utilized these spaces, but the spaces themselves did not arise to serve the artwork. Similarly, the authors contended, many biological traits might be structural necessities or incidental consequences of other evolved features, subsequently co-opted for a function, or simply remaining as non-functional byproducts.

This architectural metaphor was used to illustrate a broader critique of the "adaptationist programme," which Gould and Lewontin characterized as an approach that atomizes organisms into individual traits and then constructs adaptive narratives for each trait, often without rigorous testing. They argued that this approach often leads to "just-so stories" – plausible but unfalsifiable explanations for traits that might have alternative, non-adaptive origins. The paper also invoked Voltaire's character Dr. Pangloss from Candide, who famously believed that "all is for the best in this best of all possible worlds," to satirize the tendency to see every biological feature as perfectly designed and optimally adaptive.

Core Tenets of the Critique

Gould and Lewontin outlined several alternative explanations for the origin of traits that the adaptationist program, in their view, often overlooked:

• Byproducts (Spandrels): Traits that are incidental consequences of the development or evolution of other features. For example, the redness of blood is a byproduct of hemoglobin's oxygen-carrying properties, not an adaptation for redness itself.
• Developmental Constraints: Limitations on the range of possible phenotypic variation due to the organism's developmental pathways. Evolution can only work with the raw material available, and certain forms may be impossible or highly improbable to achieve.
• Genetic Linkage: Traits that are not themselves adaptive but are genetically linked to other traits that are under selection.
• Random Processes: Genetic drift, founder effects, and other stochastic events can lead to the fixation of non-adaptive or even slightly deleterious traits, especially in small populations.
• Historical Contingency: The path of evolution is not always optimal; past evolutionary events can constrain future possibilities, leading to suboptimal but historically entrenched solutions.

The paper did not deny the importance of natural selection but sought to broaden the explanatory toolkit of evolutionary biology, urging researchers to consider a wider range of evolutionary mechanisms beyond direct adaptation. It advocated for a more holistic view of organisms, recognizing that traits are integrated within complex developmental and genetic systems, rather than existing as independent units for selection to act upon.

Impact and Symbolism in Evolutionary Psychology

"The Spandrels Paper" quickly became a landmark publication, sparking extensive debate and influencing multiple fields, including evolutionary psychology. Within evolutionary psychology, the paper's arguments are frequently invoked in discussions about the nature of psychological adaptations and the appropriate methodology for identifying them.

Proponents of the adaptationist program in psychology, such as Tooby and Cosmides, argue that the human mind is composed of numerous domain-specific psychological adaptations, each designed by natural selection to solve recurrent problems faced by our ancestors. They contend that the mind is not a general-purpose learning device but a collection of specialized "mental organs" or "modules." From this perspective, the challenge is to identify these adaptations and their specific functions.

Critics of this strong adaptationist stance in evolutionary psychology often draw upon Gould and Lewontin's spandrels concept. They suggest that many human psychological traits, behaviors, or cognitive biases might not be direct adaptations but rather byproducts of other evolved capacities. For instance, some argue that artistic ability or musicality might be spandrels – incidental byproducts of complex cognitive capacities evolved for other purposes (e.g., language, fine motor control, social bonding) – rather than direct adaptations for art or music themselves. Similarly, some argue that certain cognitive biases or even some forms of psychopathology could be non-adaptive byproducts of otherwise adaptive cognitive architectures, rather than direct adaptations or maladaptations.

David Buller, for example, has critiqued what he perceives as an overreliance on adaptationist explanations in evolutionary psychology, echoing Gould and Lewontin's concerns about "just-so stories" and the difficulty of empirically testing adaptive hypotheses for complex psychological traits. He emphasizes the need for more rigorous empirical evidence to distinguish between adaptations, byproducts, and other evolutionary outcomes.

Enduring Relevance and Critiques of the Critique

While widely cited, Gould and Lewontin's paper itself has also faced critiques. Some argue that it misrepresented the actual practice of adaptationists, who, even before 1979, often considered constraints and alternative hypotheses. Others contend that the paper's emphasis on non-adaptive explanations inadvertently discouraged research into the adaptive functions of traits, or created a false dichotomy between adaptation and constraint. For instance, some argue that byproducts themselves can subsequently be co-opted by natural selection, becoming exaptations (a term Gould and Vrba later introduced), blurring the line between spandrel and adaptation.

Despite these debates, "The Spandrels Paper" remains a powerful and enduring symbol in evolutionary thought. It serves as a perennial reminder to consider the full spectrum of evolutionary mechanisms and to maintain a critical stance towards explanatory narratives, especially when considering the origins of complex biological and psychological traits. Its core message – that not everything is an adaptation – continues to shape discussions about the proper scope and methodology of evolutionary explanations across biology and the behavioral sciences.