Chapter 12 shows that high heritability and strong environmentally driven change are both possible in the same trait. By providing an appropriate diet to people with PKU, reducing lead exposure to children, and treating iodine deficiency, it is possible to either increase intelligence or prevent large drops in intelligence. These environmental interventions are major successes that are probably responsible for millions of people being smarter today than they would have been otherwise. Adoption studies also show that being raised in a middle- or upper-class family home probably raises IQ scores by as much as 4–5 points, an increase that would have major positive impacts on people’s lives (see Chapter 11).