“The question is, did intelligence evolve because the smarter members of the population could avoid getting killed off? In prehistoric times, this would involve finding the best foods and avoiding enemies; in modern times this means staying in shape, not smoking, and avoiding violent lifestyles.”

This is slightly misleading. Smoking, for example, generally doesn’t kill until long after reproduction has occurred, after genes have already been passed to offspring. If you are making a direct comparison between prehistoric and modern man, it’s still mostly a question of living long enough to pass on your genes.

Natural selection is another story. Smokers may be less desirable than non-smokers, and that may provide less opportunities to mix with “good” (e.g. intellient) genes, which is more to the point of this article.