Is there a dysgenic secular trend towards slowing simple reaction time? Responding to a quartet of critical commentaries

Previously Woodley, te Nijenhuis and Murphy (2013) tested the hypothesis that Victorian era British and American samples exhibited higher g on average than relatively more modern populations sampled from the US, UK, Canada, Australia and Finland, using measures of simple visual reaction time in a meta-analytic study. Based on 13 age-matched studies from Western countries conducted between 1884 and 2004 yielding 16 data points we estimated a decline of − 13.35 IQ points. Here we respond to a quartet of critical commentaries on our paper penned by five prominent intelligence researchers (James Flynn, Theodore Nettelbeck, Irwin Silverman, Julia Dodonova and Yuri Dodonov). We show via various reanalyses of the data and also via careful consideration of the arguments presented that the original finding of a potential secular decline in simple reaction time performance is robust. A recurrent criticism of our finding stems from earlier work showing no secular trends with respect to inspection time over a 20-year period in Australia despite the possibility of co-occurring dysgenic fertility. We deal with this via the method of correlated vectors, which reveals the presence of a 'genetic g' common factor on which simple RTs, WAIS g loadings and subtest heritabilities load positively and significantly, but on which inspection time does not load. This indicates that inspection times are associated with local information processing, unlike simple reaction times, which are associated with global processing (i.e. g). The robustness of our original finding is best illustrated however by our final meta-regression, in which the use of six methods variance-controlled reaction time means taken from the US and the UK between 1889 and 1993, coupled with a newly-estimated age-matched reference standard deviation, reveal a seemingly robust secular trend towards slowing reaction time in these two countries, which translates into a potential dysgenics rate of − 1.21 IQ points per decade, or − 13.9 points in total between 1889 and 2004. We conclude by arguing that the best way forward is to test novel predictions stemming from our finding relating to molecular genetics, neurophysiology and alternative cognitive indicators, thus shifting the research focus away from the purely methodological level towards the broader nomological level. We thank our critics for helping us to arrive at a much more precise estimate of the decline in general intelligence.