Razib Khan and Emil Kirkegaard have estimated the average IQ by college major using GRE and SAT scores, though I am fortunate enough to possess the Project Talent dataset, which has both IQ scores (measured at ages 12-18, for most) and college majors. They also test verbal/visual/mathematical ability, so I took advantage of that and plotted ability tilts by major, using the method Razib Khan used.
Did Project Talent specify what tests they used to get those IQ scores? I find it very hard to accept that Zoology/Philosophy or a foreign language is just 1 IQ point below math majors. In fact, the math major scores are quite low.
My personal observation of the university I went to (a public elite university) suggests that people in the pure sciences (math, physics, chemistry) are at the top. Followed by engineering and then by business, finance, economics.
All humanities majors like philosophy, history, women's studies, journalism, english majors, etc are the bottom of the barrel. Most of these women (and yes, most are women) are barely above 100.