Unrelatedly, the author's odd name "Michael Woodley of Menie" caught my eye. It would seem that he's the heir to a Scottish barony (Menie). I hesitate to even go there, but it's at the very least interesting that the (supposed) decline in general intelligence since the Industrial Revolution is being studied by an ancestral nobleman.
Edit: after reading the article and following up on the author's affiliation, the Ulster Institute for Social Research, this is definitely something to be taken with a grain of salt. The Ulster Institute has ties with "racialist" fringe scientists promoting what is essentially a 21st century take on eugenics. The paper is not necessarily inherently flawed because of this, but certain assumptions in it (like the uncited claim that lower socioeconomic classes have been historically correlated with lower g) seem fishy to me as a result.