Why does IQ vary as much as it does?

Describe the Myers-Briggs Type Indicator (MBTI) personality framework and the Big Five model,
December 22, 2020
What is the usual relationship between adult children and their parents?
December 22, 2020

Have scientists found the source of g?

1. What does cross-sectional research on IQ throughout adulthood usually find?

2. What does longitudinal research on IQ throughout adulthood usually find?

3. How do historical changes affect the results of longitudinal research?

4. How does cross-sequential research control for cohort effects?

5. Why does IQ vary as much as it does?