-so, only a fraction of humanity will have access to changing themselves to be smarter and stronger.
Evolution was NEVER an equal possibility process.
This fraction of humanity will outcompete the rest - as in they/ their descendants will survive and the rest will dissappear, going the way of the dinosaurs -, as has happened many, many times in the history of life on Earth.
-even today, very few natural disasters can endanger a race of humanity as a whole - these are the type of disasters that endanger all of humanity (a gigantic asteroid, few others).
The regional disasters you mentioned don't even come close.
And that's just plain old "survival of the fittest" evolution like we've already had for millions of years. Significantly, we don't actually control which genetic modifications become the prevalent ones, or which populations in a competing genetic arms race actually win the battle for supremacy. Just because intelligent agency is involved doesn't change the underlying mechanism.
Of course the underlying mechanism doesn't change.
What does change is the fact that slow random genetic mutations are replaced with fast intelligent modifications, genetic OR otherwise, which WILL give desirable traits (intelligence, for one).
But humans still cannot directly control which traits proliferate and which ones die out, especially on the timescales on which evolution actually occurs. Measurable speciation can take hundreds or thousands of generations to produce consistent phenotypical differences, and then even longer for those emerging (and otherwise superficial) racial differences to actually produce a separate species
You might as well suggest that the sudden prevalence of diabetes and autism are major turning points in human evolution. The fact is, evolution occurs with gradual trends over a ridiculously long period of time; even things that buck the trend -- a genetically modified race of superhumans, for instance -- wouldn't even register on nature's evolutionary radar, UNLESS we were able to maintain the genetic purity of that modified race for something like half a million years and prevent them from ever cross-breeding with ordinary non-modified humans. I don't really see that happening unless the superhumans either colonize another planet and then glass the Earth on their way out, or the entire human species bombs itself back into the stoneage and starts over with the isolated pockets of survivors from around the globe.
It remains ruthless. But it's no longer slow.
No, it's still quite
slow. The thing a lot of people don't understand is that the genetic makeup of a species ALREADY has a lot of variation built into it, so even genetic modification only takes place within the standard margins of allowable variations (e.g. locating and activating genes that correlate with higher intelligence or athletic ability). That's really just artificially raising the frequency of specific traits already inherent in the human genome.
Those kinds of changes aren't evolutionary
changes. If the entire human race became four times smarter and with across-the-board natural immunity HIV and cancer, we would still be human beings, albeit a distinct RACE of humans that has never existed before (a certain passionate statesman once referred to such a strain of enhanced humans as "the Master Race"). Evolution, though, doesn't work with the goal of improving
species, but merely adapting them to their environment. So over, say, two million years you end up with a race of extremely athletic humans with no body hair, extremely pale skin, and on average are thirty percent smaller, with vastly reduced color perception in favor of greater acuity of fine detail.
In other words, whatever we INTEND to create with the Master Race, the fickle and slow acting forces of evolution may inevitably transform us into a race of albino colorblind dwarfs. Not because anyone PLANNED it that way, but because from the aggregate of highly successful offspring producers over the millions of years humanity existed, the ones who produced the most offspring just happened to carry a slightly larger proportion of the "short/pale/hairless" genes than the "tall/bronzed/fuzzy" genes.