Larger, but also more diverse, genetically.

Hmm? How does recombination not increase genetic diversity?

NS does not actively select for or against anything in particular. What happens is that those who are more biologically fit end up contributing relatively more (quantity and diversity) to the gene pool. What happens after that may or may not be 'survival of the fittest', which is a very loaded terminology.

I've used the word fit, in this context, to mean biological fitness, but survival of the fittest generally means the 'hardiest' or 'most resilient', etc. But in nature, biological fitness and 'hardiness' are not usually linked. For example, in bacteria, the presence of antibiotic resistance genes ('hardiness' ) is usually associated with lower biological fitness. Clostridium difficile colitis is a frequent enough example of this. C. difficile is an organism that lives in the digestive tract of normal-asymptomatic people, but it has relatively low biological fitness. It does not reproduce as quickly as other flora of the digestive tract. However, when a broad spectrum antibiotic is administered to the individual, the bacteria without antibiotic resistance die, leaving the C. difficile to flourish in their place. Stopping the administration of broad spectrum antibiotics generally leads to repopulation with the normal intestinal flora over time. That is an example of natural selection. It does not necessarily select for any particular characteristic.


It does cause certain traits to be overrepresented in the gene pool, but there will still be new genotypes produced as a result of mutation and recombinations. These may not be the most 'biologically fit' as in the case of the antibiotic resistance gene.

Well, first of all a small nitpick, but there is no probability involved. Fitness is defined by the number of offspring produced (not potential offspring, but number actually produced). So having greater fitness means you've already contributed relatively more to the gene pool.
Second, yes those who have higher biological fitness contribute more to the gene pool. On the other hand, the reverse is not necessarily true. In the case of an adverse event, like an antibiotic, those who subsequently contribute more to the gene pool are not necessarily those who were the most biologically fit prior to that event. These types of events tend to be random over time, and natural selection does not 'plan' or 'guide' which traits should be expressed beforehand.