If EVERYONE had the average IQ, mankind would probably have recently advanced from the Stone Age. 100 IQ is not particularly intelligent.
100 IQ today isn't what it used to be, either.
From wikipedia:
Intelligence Quotient
"Historically, IQ was a score obtained by dividing a person's mental age score, obtained by administering an intelligence test, by the person's chronological age, both expressed in terms of years and months. The resulting fraction (quotient) was multiplied by 100 to obtain the IQ score. For modern IQ tests, the raw score is transformed to a normal distribution with mean 100 and standard deviation 15. This results in approximately two-thirds of the population scoring between IQ 85 and IQ 115 and about 2 percent each above 130 and below 70."
This link from wikipedia:
IQ Classification is an interesting read.
The way in which Intelligence Quotient is determined has changed in recent years.
In the past, someone's score on an IQ test was based on their individual performance against the test questions, and the test-taker's age. The top of the bell curve corresponded with an IQ deemed to be 100, and approximately 60% of test takers had scores in the 90-110 range.
Under the current IQ deviation method, 100 IQ is deemed to be the mean average of performance by all test takers, and the top of the bell curve.
While it may seem to some that the difference between these methods is only the choice of grammatical syntax, the methods are actually significantly different:
Lets assume that an IQ test has 100 questions of increasing difficulty, with a 50 minute time limit. The same test is given to a random group of statistically significant size in 1974, and again in 2024.
Lets assume that a score of 50/100 corresponded with an IQ of 100 in 1974, with 55 correct being 110, and 45 correct being 90.
Discounting the fact that a greater percentage of the random group in 2024 would not be as fluent in English because of immigration policies, if the mean average performance was now 45 correct answers instead of 50, what used to be an IQ of 90 is now considered to be 100. Effectively, average intelligence is now considered to be normal intelligence.