I agree that intelligence is a skill. If you don't practice critical thinking it will not come as easily when trying to solve a problem.

I think that people all have the same potential for intelligence at conception but their environments start limiting them even before birth. However people born with genetic abnormalities such as Down's Syndrome I would agree don't have the same intelligence frame as the average person. If there is a genetic component it will manifest right away.

It is well know that early exposure to lead lowers a child's intelligence. What is not as well known is that a baby will get a portion of it's mothers heavy metal load. So if a mother has a higher burden of mercury and lead their child will be less likely to have a higher IQ. Flouride, Aluminum, vaccine injury all can lower your intelligence. Also how you treat your brain during puberty while it is rewiring is a big factor in intelligence. I am scared for all the kid on medication like Ritalin while undergoing puberty. Think about all the people who "fried their brain" from drug use. Their decreased IQ is a result of environmental exposure.

There are also multiple forms of intelligence IQ only captures a couple of them.

The emotional environment is a huge factor for cognitive development.

I would say that higher IQ is a negative factor from a evolutionary point of view since higher IQ individuals tend to delay having kids when in college and will tend to make sure to use birth control and not have accidental pregnancies. Not a lot of intelligence required to have sex.