IQ Advanced Like Height [...]

In fact, the answer is not so puzzling if you compare it to another trait that has slowly grown over the decades: body height. Within one generation you will find that tall parents have taller children, and short parents have shorter children, showing a large genetic component; but if you compare different generations, you will find we are all much taller than our grandparents – and that’s not because our genes have changed. It’s because modern life, with better medicine and diet, has allowed our bodies to grow. (Source)

There is a more general card on the Flynn Effect