As far back as 2006 Bruce Lahn noted that microcephalin was linked to lower intelligence. His University then counselled him that he would be better off working on other matters. Danielle Posthuma took up the challenge and, in a triumph of empiricism, failed to replicate the result. That’s right. Failure to replicate is a success for knowledge. I smiled when I heard her present the results in Amsterdam in 2007, because if such research had been frowned upon world wide, rather than just in the US, then we would have imagined that the microcephalin effect was true, but suppressed by political pressure. Odd, how jumpy people are when they don’t want to know that intelligence differences are due to the genes (but fearfully believe it anyway), whereas us poor souls think such hypotheses depend on the evidence.
Now we have the sequel, Microcephalin II. Michael Woodley (passim) will be well known to readers of this blog and Heiner Rindermann; Stratford, Ed Bell and Davide Piffer will be joining him in the halls of fame. They have investigated the pattern of population level correlates of MCPH1 and ASPM frequency counts and IQ. They find evidence for a substantial mediation effect stemming from health-status variables, which hints at a possible new role for MCPH1 in particular as an immune system boosting gene.
Woodley, M. A., Rindermann, H., Bell, E., Stratford, J. & Piffer, D.
(2014). The relationship between Microcephalin, ASPM and intelligence: A
reconsideration. Intelligence, 44, 51-63.
Despite the fact that the recently evolved Microcephalin and the related
Abnormal Spindle-like Microcaphaly Associated (ASPM) alleles do not
appear to be associated with IQ at the individual differences level, the
frequencies of Microcephalin have been found to correlate strongly with
IQ at the cross-country level. In this study, the association between
these two alleles and intelligence is examined using a sample of 59
populations. A bivariate correlation between
Microcephalin and population average IQ of r = .790 (p ≤ .01) was found,
and a multiple regression analysis in which the Human Development Index,
Disability Adjusted Life Years (DALY) lost due to Infectious diseases,
DALY Nutritional deficiencies, and Würm glaciation
temperature means were included revealed that Microcephalin remained a
good predictor of IQ. Path analysis, with both direct and indirect paths
from Microcephalin to intelligence, showed good model fit. These
multivariate analyses revealed strong and robust associations between
DALYs and Microcephalin, indicating that the former partially mediates
the association between the latter and IQ. A second smaller
correlational analysis involving ten country-level estimates of the
frequencies of these two alleles collected from the 1000 genomes
database replicated this pattern of results. To account for the findings
of this study, we review evidence that these alleles are expressed in
the immune system. Microcephalin is strongly associated with DNA repair,
which indicates a special role for this allele in the intrinsic
anti-viral immune response. Enhanced immune functioning may have
advantaged both hunter–gatherer and agrarian societies coping with the
heightened disease burden that resulted from population growth and
exposure to zoonotic diseases, making it more likely that such growth
and concomitant increases in intelligence could occur.
Get the whole paper here: https://docs.google.com/file/d/0B3c4TxciNeJZM0tSWERNVUlrdzQ/edit