Biological evolution is a bit misnamed. Evolution is often understood to have a set direction or purpose, and that is not the case here.
Human choices (mainly dealing with medicine) do indeed interfere with natural seletion and therefore with evolution. It does not theorically make the development of things like wings or additional functional limbs impossible, but it does make them less likely to become widespread if they ever occur.
More generally, since the last few centuries have seen considerable effort towards ensuring the best possible odds of survival and of having fertile offspring to people of all genetic makeups, it seems to me that, if our more insane drives can be reigned in and humanity survives a few thousand centuries more, we will eventually see the more-or-less symultaneous and spontaneous arising of a handful of new human subspecies - say, one with functional nictating membranes between the fingers, another capable of making its own Vitamin C internally, and yet another that actually functions better at night than during daytime. A million years or so later, an actual new species might perhaps come to be, one that can no longer be considered Homo Sapiens.
But all that is ignoring genetic techniques. Alone among animals, humanity can now purposefully direct its own genetic future, both by direct manipulation and by a more mundane choice of reproductive mates. If we choose to, we may for instance make albinism or hemophily more widespread, or make distinct ethnies a very subjective classification. I don't think that is too likely to happen, however. The emotional and ethical challenges are too great.
As for mental aspects, it must be understood that while they are indeed covered by biological evolution, it is not in any way that ensures their continued growth in any meaningful way. We are theorically just as likely to become bruter and dumber along generations as we are to become more mentally capable and perceptive. We do have, for instance, a perception bias towards movement as opposed to detail, because such a bias proved useful in avoiding predators and rivals in the past. We (or more accurately, some specific subgroup of humanity) might eventually spontaneously develop the opposite bias, but it may take millions of years.
That is, if we are talking about biological potential alone. Besides the conscious choice of directing evolution that I mentioned above, and which is so far not shared by any other lifeforms, we must also consider that language and the capability for abstract thought are remarkable capabilities, that in many senses trump and surpass biological limitations. Your second post does not refer to biological evolution at all, but instead to the development and use of educational and societal structures that lead to better use of our mental potential. IMO we could probably jumpstart the development of, say, a chimp spoken language in a few thousand years if we choose to. It would take a lot of chimps, probably more than live these days, and a lot of effort, but it is probably possible. It would be even faster if we went all the way to breed generation after generation of chimps for their mental potential, which is perhaps not ethically sound. But assuming such a development to be possible, they would very soon participate in the mental game as well, and learn things such as mathematics and abstract concepts. Just like we did.
