Degeneracy

Introduced to the wiki by Barrett (2017), where it is the mechanism that makes the whole constructionist argument go through. Edelman & Gally’s (2001) term: dissimilar structures giving rise to the same function.

Not redundancy. Redundancy duplicates identical elements (two copies of the same part); degeneracy achieves the same outcome by different means (two different parts that both work). Barrett is pointed about the distinction — redundancy “is inefficient and to be avoided,” whereas natural selection favours degeneracy because it delivers robustness and evolvability at once (Whitacre & Bender, 2010).

Why it matters for emotion

The argument is one step long, which is what makes it powerful and what makes it suspicious.

In emotion research, degeneracy means that instances of an emotion (e.g. fear) are created by multiple spatiotemporal patterns in varying populations of neurons. Therefore, it is unlikely that all instances of an emotion category share a set of core features.

No shared facial expression. No shared autonomic pattern. No shared set of neurons. The summary representation of a category — the thing that shows up when you average across a sample — is “an abstraction that need not exist in nature.”

That single move reframes the entire empirical record this wiki holds. The failure to find emotion-specific autonomic signatures (autonomic-specificity-of-emotion) and the failure to find consistent-and-specific brain regions (locationist-vs-constructionist-brain-emotion) stop being failures of measurement or of statistical power. They become what a degenerate system predicts.

The evidence Barrett recruits

Degeneracy is not invented for emotion; it is imported, and the imports are the strongest part of the case:

• Patient Roger, who lost his limbic circuitry to herpes encephalitis, still experiences emotions (Feinstein et al., 2010).
• Monozygotic twins with Urbach–Wiethe disease — both with fully calcified basolateral amygdalae, genetically and environmentally matched — have “markedly different emotional capacity” (Becker et al., 2012; Mihov et al., 2013). Same lesion, same genes, different outcome.
• Heritability without genes: a characteristic can be highly heritable with no single set of necessary and sufficient genes (Turkheimer et al., 2014).

The twins are the sharpest case, because they hold constant everything a locationist account would appeal to and still get divergence.

The tension with LeDoux, which is real

LeDoux’s resolution objection (see amygdala) and degeneracy are two explanations of the same observation, and the wiki should not let them blur.

Observation: the same region activates across many emotion categories.

• Degeneracy (Barrett): many different neural patterns → one category. Area-level similarity is real similarity; the variability is in which pattern implements the instance.
• Resolution (LeDoux): area-level similarity conceals cell-population-level difference — distinct mating and intruder-attack populations within the ventromedial hypothalamus, invisible at voxel scale (Lin et al., 2011).

These are not the same claim, and they point opposite ways. Degeneracy says the many-to-one mapping is a genuine feature of the system. LeDoux says the apparent many-to-one mapping is an artefact of a blunt instrument, and there are crisp one-to-one mappings underneath. Barrett’s counter is that neurons are multipurpose “even in subcortical regions like the amygdala” — sourced, unfortunately, to a personal communication.

Nothing in this wiki adjudicates it. It is the most tractable open question in the wiki’s emotion-anatomy material, because it is a question about measurement rather than about metaphysics.

The falsifiability cost

Degeneracy is what makes the theory-of-constructed-emotion hard to disconfirm, and the wiki should hold this alongside the theory rather than as an afterthought. If instances of a category are predicted not to share features, then finding that they do not share features confirms the theory, and finding that they do would presumably be read as a well-chosen sample rather than a refutation.

Note the symmetry with homeostatic-property-cluster-kinds, which does the same work for Scarantino’s New BET from the opposite side of the dispute: HPC kinds have no necessary properties, so variability is predicted rather than refuting. Two rival theories, both of which have made variability their prediction. The evidence that was supposed to decide between basic emotions and construction now decides nothing, and it is degeneracy on one side and HPC kinds on the other that produced the stalemate.