Why are atheists so much smarter than christians and muslims?

yeah I believe some of those points are statistically the same but i agree that this effect may be that people with higher IQs tend to question religion more and unsatisfied with the answers leave it. but i also question the data since by definition IQs should have a normal distribution with the center at 100 and in that plot there seem to bee a lot more people below 100 regardless of faith.