The nature-vs-nurture argument rarely gets as heated among scientists as when it comes to the question of human intelligence. Are we born with a certain level of intelligence, or do we acquire a lot of our IQ from our social environment after birth? It’s a thorny question. Plenty of genes are known to be key in the expression of human intelligence, and turning them on and off can have marked effects.
But now the debate is set to become even more involved. An international team of researchers from the Charité-Universitätsmediz in Berlin set out to explore the traits inherent in a select group of genes among 1,500 teenagers. The scientists then compared the results with intelligence scores that the teens had as well as with some of their neurological traits.
What they discovered, say the researchers who published a study in the journal Translational Psychiatry, was a manifest relationship between the epigenetic modifications of a specific gene called “dopamine receptor D2” (DRD2) and general intelligence. This finding indicates, they say, that our life experiences can affect both the wiring of our brain and even how some of our genes get expressed in our thinking and behavior.
“One possible explanation for the strong malleability of cognitive performance measure is that environmental factors modify gene expression via epigenetic mechanisms,” the researchers explain. “Epigenetic factors may help to understand the recent observations of an association between dopamine-dependent encoding of reward prediction errors and cognitive capacity, which was modulated by adverse life events.”
The field of epigenetics is the scientific study of heritable changes in gene expression (active versus inactive genes) that do not involve changes to the underlying DNA sequence. Scientists have long known that when it comes to intelligence we are not born with a rigidly predetermined set of mental capacities. Rather, those capacities remain subject to environmental factors as children develop. If children live in resource-rich environments with loving care from parents, they have a far higher chance of becoming smart and well-rounded than if they grow up in grinding poverty facing neglect or outright abuse.
Research of this kind is essential for helping us understand how environmental factors can influence the mental capacities that youngsters acquire through their childhood and adolescence. This is so especially in the face of ongoing climate change that is set to trigger a cascade of environmental disasters from extreme weather to crop failures and prolonged droughts around much of the planet.
“Stress and adverse life experiences are examples of environmental factors that can affect gene activity, leading to structural changes in our genetic material (genome),” the scientists explain. “These ‘epigenetic changes’ enable the human genome to adapt to its environment, allowing our DNA to be passed on to the next generation of cells, as well as passing on the information that determines whether, and under which conditions, a particular gene will be activated.”
The neurotransmitter dopamine plays an important role in our brains’ reward system and influences our level and nature of drive and motivation. The researchers managed to establish a clear link between the epigenetic regulation of dopamine neurotransmission and a person’s IQ test performance. “Epigenetic modification resulted in the dopamine receptor gene being silenced: neurons carried fewer dopamine receptors, and signal transmission was reduced,” they say.
“We have previously been able to observe links between stress and cognitive performance, particularly in relation to the activity of the dopamine-controlled reward system,” explains Dr. Jakob Kaminski, a lead researcher of the study from Charité’s Department of Psychiatry and Psychotherapy. “Environmentally-induced gene activity now joins the ranks of other factors known to influence IQ test performance, such as poverty and genetic constitution.”
