Intelligence, like . Everything else we have, is from genetics + environment. Long ago, i heard the famous geneticist, dave smith, say it was more linked to maternal than paternal iq. Truth is, we get equal #'s of genes from mom & dad. Children of moms who didn't graduate from hs have 7x the risk of the gen'l population for intellectual disability, maybe because moms still impact a child's environment more than dads.
"g factor" For about 40-50% of the traits measured in an iq test, doing well (or not) in one correlates very highly with doing well (or not) in another. It seems there is something they all have in common, and this unknown something is called the g-factor. It also appears to be the mostly highly heritable component of iq. Many theories exist as to what g is. It appears much like cpu "processing speed".