Steve Hays recently made the following point, with which I'd agree:
Physicists have a reputation for being the smartest scientists. Smarter than biologists. That's ironic since biology is far more varied and complicated than physics, so–if anything–you'd expect great biologists to be smarter than great physicists.
Just to add to Steve's thoughts:
1. I suppose some of this is self-perpetuated by physicists as a community. For example, people like Richard Feynman and Murray Gell-Mann seem to have incessantly talked about how smart they were or are.
2. Plus, I think the most impressive scientific discoveries in the first half or two-thirds of the 20th century, certainly to the public if not also impressive in their own right, have largely been in physics (e.g. Bohr's model of the atom, Einstein's theories of relativity, the big bang theory, QM).
3. Not to mention the technological applications in the wake of these discoveries in physics (e.g. nuclear weapons, spaceflight, maybe modern computers to an extent - although I think computers are probably better attributed to mathematicians such as those who served as code crackers in WW2).
4. All this presumably gives the public the impression that physicists are like modern wizards (e.g. able to unlock the inner workings of the atom to harness nuclear energy).
5. Related, I've also read JFK's administration really pushed science, math, and engineering on the American public mainly in order to compete with the Soviet Union in the space race (e.g. to land a man on the moon). I could be wrong, of course, but I assume this would positively affect the perception of these fields in the minds of most of the public, if not also make the public think these are the fields all the really smart students should strive for.
6. However, as we know, it seems there haven't been as many momentous moments in physics in recent years. Today some even joke physics is far too speculative (e.g. string theory, multiverse).
7. My impression is biology started really taking off as a field around the time when physics began to wane, say, around the middle of the 20th century. Such as with physicist Erwin Schrödinger's What Is Life? series of lectures. And especially with the discovery of the structure of DNA by Watson and Crick. Crick himself of course was a physicist turned biologist.
From DNA, we learned about genes, chromosomes, etc., at least on levels deeper than Mendelian genetics.
This coincided with medical discoveries and applications like Fleming's discovery of penicillin as an antibiotic.
Likewise, people began to apply mathematics to biology (e.g. population genetics - which with Darwinism and genetics now form the neo-Darwinian synthesis).
In our time we've had the sequencing of the human genome, among other genomes. And there still seem to be so many discoveries awaiting scientists working in biology or related fields (e.g. biochemistry, pharmaceuticals).
In any case, perhaps future generations who have lived through this era where it seems physics is waning while biology is waxing or on the rise will have a different impression than previous generations who have lived through the apogee of physics.
8. For better or for worse, many smart people primarily chase the money. For instance, rather than going for a PhD in something they could do like physics, and hoping for an academic career, some people decide instead to stop at a bachelor's degree in order to try their hand working for a large company in Silicon Valley like Google or Pixar. Of course, one can still do significant research at these companies, but is the opportunity cost vs return worth it for them?
9. I suppose the truth or at least in the direction of the truth is that the smartest people are those who are fluent in abstract and analytical reasoning and able to apply it to whatever field they're interested in (e.g. theology, philosophy, mathematics).
10. By the way, I think William Dembski, for one, who I'm sure could've done physics if he wanted to, but instead chose to apply himself more to the biological sciences side of ID, is considerably smarter than physicists like Victor Stenger or Lawrence Krauss. I think it might even be arguable Dembski is on par with Stephen Hawking or Roger Penrose. Of course, Dembski gets such a bad wrap due to his Christian beliefs.