The biology of intelligence: From association to mechanism

Advances in the molecular genetics of the nervous system are important in understanding the nature of human intelligence differences and their changes with age. As a case study for such research we discuss recent research on apolipoprotein E (ApoE). The gene for ApoE (the APOE gene) shows polymorphism in humans. The epsilon 4 allele is associated with increased incidence of Alzheimer's disease and lesser forms of cognitive dysfunction as people grow older. Such cognitive dysfunction appears often to be the interaction between possession on the epsilon 4 allele of APOE and brain insults such as head injury, cardiac bypass surgery and intracerebral haemorrhage. The mechanisms by which the ApoE epsilon 4 isoform might increase the vulnerability of the brain to insults are presented. Implications for research on human intelligence are discussed.