I saw this on a website:
There are at least 150 genes linked to intelligence on the X chromosome, and verbal IQ is definitely known to be X-linked.
A female inherits x from father and x from mother. They will both influence her intelligence – I guess giving her the average of both parents. A male inherits the x chomorsome only from his mother. That means a male’s intelligences will only be influenced by one x chomrosome – his mother’s. This can explain why so many more males than females have IQs below 70 but also why 20% more males than females have IQs above 140.