title: By their words ye shall know them: Evidence of genetic selection against general intelligence and concurrent environmental enrichment in vocabulary usage since the mid 19th century.
abstract: It has been theorized that declines in general intelligence (g) due to genetic selection stemming from the inverse association between completed fertility and IQ and the Flynn effect co-occur, with the effects of the latter being concentrated on less heritable non-g sources of intelligence variance. Evidence for this comes from the observation that 19th century populations were more intellectually productive, and also exhibited faster simple reaction times than modern ones, suggesting greater information-processing ability and therefore higher g. This co-occurrence model is tested via examination of historical changes in the utilization frequencies of words from the highly g-loaded WORDSUM test across 5.9 million texts spanning the period 1850-2005. Consistent with predictions, words with higher difficulties (δ parameters from Item Response Theory) and stronger negative correlations between pass rates and completed fertility declined in use over time whereas less difficult and less strongly selected words, increased in use over time, consistent with a Flynn effect stemming in part from the vocabulary enriching effects of increases in population literacy. These findings persisted when explicitly controlled for word age, changing literacy rates and temporal autocorrelation. These trends constitute compelling evidence for the co-occurrence model.
authors.affiliation: Department of Psychology, Technische Universität Chemnitz, Chemnitz Germany ; Center Leo Apostel for Interdisciplinary Studies, Vrije Universiteit Brussel, Brussels Belgium.
authors.forename: Michael A Woodley Of
authors.initials: MA
authors.lastname: Menie
authors.affiliation: Departments of Psychology and Genetics, Federal University of Rio Grande do Sul, Porto Alegre Brazil.
authors.forename: Heitor B F
authors.initials: HB
authors.lastname: Fernandes
authors.affiliation: Department of Psychology, University of Arizona, Tucson, AZ USA.
authors.forename: Aurelio
authors.initials: A
authors.lastname: José Figueredo
authors.affiliation: Department of Biochemistry, Ross University School of Medicine, Portsmouth Dominica.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Meisenberg
keywords: Flynn effect; WORDSUM; co-occurrence model; intelligence; vocabulary