This is bullshit. Here's why:

Intelligence exists. Some people are smarter than others. Some people are just plain dumb. This is easy to see.

It is hard to measure intelligence. Example: studies show that African Americans do about 15 percent (!!!) worse on IQ tests when they are told that they are taking intelligence tests. Yep - subjective feelings about intelligence (and its value) can have drastic effects on IQ test performance.

Insert other relevant studies that I forgot about because I was a slacker in psych class.

The Bell Curve is thought provoking. It is also highly questionable. Don't take it as gospel.