[AlexandrB]

IQ is not an objective measure of innate intelligence, hence it creeps up over time: http://en.wikipedia.org/wiki/Flynn_effect

Since this effect is so rapid (~100 years), it is unlikely be due to genetic changes. It's pretty clear that developmental and social factors are playing into IQ test results. Both of these are negatively affected by being born into a low income family (less access to food, learning materials, mentors, other IQ individuals, etc.).