A person’s intelligence is determined by a number of different variables that affect how people think and consume information. First, tall people are found to be more intelligent because a 2009 study found that taller children score higher on tests. The oldest child is also shown to be more intelligent, with an IQ 2.3 times higher than younger siblings, which is due to full parental attention rather, not genetics. More intelligent people also grow up consuming more alcohol and marijuana according to the Savanna-IQ Interaction Hypothesis, which suggests that more intelligent people have evolved novel values and preferences. With all these factors in mind, it’s still important to remember that correlation doesn’t equal causation, because there are many variables that affect intelligence.