Signs of a Flynn effect in rodents in the last century? Secular differentiation of the manifold of general cognitive ability in laboratory mice (Mus musculus) and Norwegian rats (Rattus norvegicus)

Signs of a Flynn effect in rodents? Secular differentiation of the manifold of general cognitive ability in laboratory mice (Mus musculus) and Norwegian rats (Rattus norvegicus) over a century—Results from two cross-temporal meta-analyses. Michael A. Woodley of Menie, Mateo Peñaherrera-Aguirre, Matthew A. Sarraf. Intelligence, Volume 95, November–December 2022, 101700. https://doi.org/10.1016/j.intell.2022.101700

Highlights
•    Cross-temporal meta-analysis of GCA variance across 100 years in rat and mice populations.
•    Evidence of GCA variance decline (differentiation) found for both.
•    Suggestive of a Flynn effect, as this is associated with differentiation.
•    Laboratory studies can directly test for this in future research.

Abstract: Substantial improvements in factors such as microbiological quality have been noted in laboratory rodent (mouse [Mus musculus] and rat [Rattus norvegicus]) populations over the last 140 years, since domestication of laboratory strains started. These environmental improvements may have caused Flynn effect-like cognitive changes to occur in these populations, perhaps if these improvements enhanced cognitive plasticity and, consequently, learning potential. While lack of relevant data precludes cross-temporal comparison of cognitive performance means of laboratory rodent populations, it is possible to estimate changes in the proportion of cognitive performance variance attributable to general cognitive ability (GCA) over time. This “differentiation effect” has been found to occur along with the Flynn effect in human populations, suggesting that environmental factors, possibly mediated by their effects on life history speed, may weaken the manifold of GCA across time, allowing for greater cultivation of specialized abilities. Meta-analysis of the literature on mouse and rat cognition yielded 25 mouse studies from which 28 GCA effect sizes could be estimated, and 10 rat studies from which 11 effect sizes could be estimated. Cross-temporal meta-analysis yielded evidence of significant “differentiation effects” spanning approximately a century in both mice and rats, which were independent of age, sex, factor estimation technique, and task number in the case of the mice, and both factor estimation technique and task number in the case of the rats. These trends were also independent of the random effect of strain in both cases. While this is suggestive of the presence of the Flynn effect in captive populations of non-human animals, there are still factors that might be confounding these results. This meta-analysis should be followed up with experimental investigation.