Short-listed for Access to Understanding 2013
organism develops? This question, often framed as the ‘nature-nurture debate’,
is one of the most fundamental problems that science has to address. Within
this debate it is of particular importance to understand how biological and
environmental factors contribute to the development of human intelligence, as
intelligence plays a substantial role in determining life outcomes. A 2011
study, published in the Molecular Psychiatry journal, has demonstrated that
differences in adult intelligence can, to a large extent, be explained by
genetic variations between people. The study therefore provides clear evidence
that a significant proportion of adult intelligence is hereditary.
scientists at 8 different universities, across 3 different countries. They
analysed DNA collected from over 3000 unrelated volunteers. Each individual’s
DNA was scanned for the presence of a large number of common genetic variations
(known as single-nucleotide polymorphisms or ‘SNPs’). These genetic variations
effectively encode the biological differences between people. Their study can
therefore reveal the genetic basis of individual differences. For example, if a
particular gene has a causal effect on a trait (in this case intelligence) then
individuals with an SNP within that gene should have noticeably different
scores on the trait compared to those who do not. Measures of each individual’s
intelligence were ascertained from various psychometric test scores collected
from each volunteer during middle to late adulthood. Two separate measures of
adult intelligence were computed: ‘crystallised intelligence’, which is a
measure of the ability to acquire and recall knowledge, and ‘fluid
intelligence’, which is a measure of cognitive skills such as abstract
reasoning, logical thinking and problem solving.
between any individual SNP and either measure of intelligence. One SNP (named
FNBP1L) was found to predict fluid intelligence, but this relationship could
not be replicated using an independent sample of data from
may be spurious. The identification of SNPs also however enables a genetic
profile of each individual to be created, a process which in effect allows the
cumulative genetic variation between individuals to be quantified. These
profiles therefore allow an assessment to be made of the extent to which more
general variations in genetic makeup contribute to individual differences.
Using this method the researchers found that 40% of the variance in
crystallised intelligence and 51% of the variance in fluid intelligence between
individuals could be explained by genetic differences. Furthermore the
predictive information contained within the SNP profile was also able to
predict intelligence scores in the independent Norwegian dataset, confirming
the validity of the original finding. These results strongly suggest that around
half the variation in intelligence between people can be attributed to
inherited abilities. Indeed as only common SNPs were analysed, rather than
every single genetic variation, the actual proportion of intelligence that is
heritable may be much higher than this.
The estimates regarding the heritability of
intelligence provided by the study are in broad agreement with those obtained
from twin and family studies. This study however strengthens our understanding
of the heritability of intelligence because it side-steps some methodological
issues that exist with twin and family studies, such as the difficultly in
parsing genetic from environmental influences when closely related individuals
are studied. The study therefore represents the first direct demonstration that
genetic differences explain a significant amount of the variance in
intelligence between individuals.
individual SNPs were found that strongly predicted intelligence, an additional
conclusion that can be drawn from the study is that a very large number of
different genes are likely to interact to determine our intelligence, rather
than there being a small number of ‘intelligence genes’. This is perhaps not
surprising as intelligence is a complex trait that is reliant on a number of different
cognitive abilities, which are in turn likely to be reliant on a number of
different biological processes. The likely influence of a large number of genes
does not suggest that associations between individual SNPs and intelligence
cannot be uncovered in the future. Instead it suggests that studies with far
larger samples, and perhaps looking at more specific cognitive abilities, will
be required in order to identify such associations. Nevertheless the study
represents an important step in the battle to understand the genetic basis of
intelligence. By improving our understanding of the biological mechanisms that
support intelligence we may be able in the future to identify ways in which the
development and maintenance of human mental functioning can be improved. This
may lead to interventions that can help to both promote cognitive abilities in
the general population, and preserve these abilities to a greater extent in old
Antony Payton, Jian Yang, Sarah E. Harris, David Liewald, Xiayi Ke, Stephanie
Le Hellard, Andrea Christoforou, Michelle Luciano, Kevin McGhee, Lorna Lopez,
Alan J. Gow, Janie Corley, Paul Redmond, Helen C. Fox, Paul Haggarty, Lawrence
J. Whalley, Geraldine McNeill, Michael E. Goddard, Thomas Espeseth, Astri J.
Lundervold, Ivar Reinvang, Andrew Pickles, Vidar M. Steen, William Ollier,
David J. Porteous, Michael Horan, John M. Starr, Neil Pendleton, Peter M.
Visscher, and Ian J. Deary
Access to Understanding entrants are asked to write a plain English summary of a research article. For Access to Understanding 2013 there were 9 articles to choose from, selected by the Europe PMC funders.
The articles are all available from Europe PMC, are free to read and download, and were supported by one or more of the Europe PMC funders.
Look out here and on Twitter @EuropePMC_news for announcements about the competition.