First of all, IQ always changes. 100 points of IQ in 2018 is not the same as 100 points of IQ in 1918. This is because IQ 100 is defined as the mean score. Man

First of all, IQ always changes. 100 points of IQ in 2018 is not the same as 100 points of IQ in 1918. This is because IQ 100 is defined as the mean score. Many things affect IQ, one of them being nutrition. If a couple with median income has 10 kids, compared to 2 kids, their ability to provide proper nutrition to those 10 kids, or the time to ensure those 10 kids are properly fed will not be as good. Fertility rates have to do with many things. Historically, fertility rates were higher because infant mortality rates were higher: fewer live births, and lower survival rate through childhood. Also, culture and religion. Some religions are against contraception of any kind and promote abstinence as the main form of birth control. Birth control requires certain form of exposure to sex education. If you had no access to education, or if your education was provided by a religious organization, it is likely you will have no proper sex ed and your risk is higher.