The Intelligence Quotient (IQ) does not measure intelligence it measures the ability of a small part of one's brain to solve puzzles.
Furthermore, since intelligence is circular the more knowledgeable you are in one subject the closer you are to being an idiot in others (the idiot savant) the IQ is helpless to measure where you are on a real scale of knowledge or intelligence.
A young baby, despite the cooing of its mother and her declarations that it looks just like it's father or brother Ted, is composed of a mess of chemicals only some of which have a connection with its parents its chromosomes have a recognizable family likeness but its intelligence may be something entirely different.
The child's intellectual development does not depend entirely on its DNA. A human's intelligence, whatever that is, is determined by additional input from its upbringing, its formal education, and its experience. It can be induced to have a Saint-like or criminal intelligence through subsequent input.
I don't know how these three influences, upbringing, formal education, and experience, affect a young child but scientifically I would expect the original chemical balance to be changed ever so slightly by thermal, electrical, and physical stresses involved in the stresses of its life. Identical fetuses will react differently to differing input and so, despite initial similarities, the adults will differ. Their intelligences may be greater or less than the norm.
On a linear scale the intelligence of a population follows the bell-shaped normal distribution from those who might be judged fools (even insane) to those who might be judged to be geniuses. There are very few at each end of the spectrum whilst the norm is what we know as a human of average intelligence. Parents may have made great efforts to move the child towards the genius end of the spectrum but the original chemical composition of its brain cells probably has an overwhelming influence on its position within the range of human intelligence. If the child is doomed to be an idiot all the schooling in the world will not produce an Einstein or a Shakespeare.
The authorities assure us that upbringing has at least as great an influence as genetics, perhaps greater. We see children of successive generations with the same interests but is this because of the teaching and influence of a succession of parents or because of an inherent chemical composition? My father, my son, and myself are very similar not just in physical appearance but also in interests. Each of the generations has enjoyed science as well as the act of writing and putting words down on paper. However, is this similarity over three generations the result of genetic transfer or upbringing? We cannot tell.
Let us assume then that the four inputs: original chemical state of the brain, upbringing, formal education, and experience, define the intelligence of the new adult. We know that intelligence can range from insanity to genius where the extremes, especially insanity, are often interpreted as illness or inherent fallibility (the fool.)
The insanity extreme, especially those that resulted in violent or non-social behavior used to be treated by surgery: the excision of some part of the brain or at least its nullification. Nowadays, surgery has given way to treatment by drugs the changing of the chemical state by the addition of other chemicals. It works, as logically it should. If insanity is not converted to genius, at least non-social behavior can be modified to NO behavior. That's better than by surgical lobotomy.
Moving down the bell-shaped distribution curve towards genius we have to explain geniuses that are otherwise odd. Sometimes they are absentminded professors but there are more extreme examples. I had a friend with a very high IQ, who was a member of the MENSA society. He declared that he couldn't speak to me because my IQ wasn't high enough. He later moved his residence from the US to Toronto, Canada, to follow his primal-scream therapist who regularly took him through rebirthing. My intelligent' friend with a very high IQ was slightly mad. Indeed, very high intelligence often borders on what society would judge to be insane.
On the other hand, moving down the intelligence scale we come to rare individuals known as idiot savants. They are characterized as being fools in all respects except one, perhaps by instantly knowing the cube root of some 25-digit number, or by being able to play an instrument expertly. They are fools with a touch of genius.
Suppose then that intelligence is really circular, that the cleverer an individual is the closer they are to lunacy, or the more foolish a person is the closer they come to genius. This model of circular intelligence has the ability to explain individuals like the schizophrenic Nobel prizewinner John Nash to the mad' Chess Champions Morphy, Steinitz, and Fischer.
John Nash did his new work before any symptoms of schizophrenia appeared but they were always there. It is genetic because his son, also a talented mathematician, has the same condition. Nash's sickness was eventually held at bay by a suitable regime of drugs to alter his brain's chemical state. Although we consider schizophrenia an illness it is a really a maladjustment of the brain chemistry. It appears more of a disease than simple lack of intellectual ability but it is not. It fits into my model of intelligence.
My uncle, a talented double-doctorate and researcher performed meteorological investigations in the Arctic and very soon afterwards worked on meteorology In Northern Africa. The sudden thermal stresses moved his intelligence from the rarity of genius to the rarity of madness.
Chess champion Morphy, a lawyer, died naked in his bath in dementia fearing poison through his clothes. Steinitz, a world chess champion and writer, also suffered from schizophrenia. He played chess with God through an open window though he never claimed to have won a game.
Fischer, having won the world championship, retired to a religious retreat not to emerge for a decade until he entered a bizarre illegal championship in Serbia. These exceptionally talented persons could be said to be mad they fit into the circle of intelligence at the point where genius and insanity meet. At this unstable point, they can be moved in either direction by drug therapy.
Can we use this information? Can we move the idiot savant towards being an absent-minded professor? Can we move the fool higher up the scale of intelligence? In theory we could by altering the chemical mix by drugs or by thermal and pressure therapy. In practice we cannot because we don't know enough to do so reliably.