Concentrators in physics, mathematics, and computer science have been the brightests ones among college students for years, see e.g.
Pure astronomy - not to be confused with state-of-the-art cosmology - and meteorology took the opposite side of the spectrum of talents in most physics & physical sciences departments.
However, such quantities such as the correlation of fields and IQ are not universal constants. There have been many signs that things may be changing a bit.
Recently I've encountered several reasons to think that theoretical condensed matter physics attracts as bright kids as theoretical high-energy physics right now. The reasons include smart kids in my Fall 2006 course as well as an analysis of PhD applicants whose folders I see every year. These very good young condensed matter physicists could easily become quantum field theorists and string theorists but they have reasons to choose condensed matter physics.
Also, biology is becoming hotter. While this field is not showing the kind of exponential expansion and progress that many people were imagining a few years ago but it still offers a large number of sufficiently interesting topics.
On the other hand, I don't think that the professional level of the people in Earth sciences is getting any better.
At any rate, these things are changing as a function of time because of many reasons and I think that it is wrong for a system to suppress flexibility in the composition of the future scientific community.