"More like "die out" than evolve out."
Yeah! That's probably the term I should have used.
But basically tho, I'm right about the stronger ones surviving which would be natural selection? Or not?
I'm not sure I'm asking this right, so bear with me.
Lemme butt in for a moment. I think the word "stronger" is a problem, or at least potentially misleading. If a creature can survive and breed, its genes get passed on to the next generation. If not, then whatever problems it had will not get passed on. It's as simple as that. "Stronger" isn't required. Maybe faster, better eyesight, better ability to digest a changing vegetation, better ability to adapt to a drier (or wetter) climate, etc. Whatever.
Over time -- lots of time -- these tiny changes in the gene pool will accumulate, and after a great number of generations the population may be quite different from the ancestral stock.
The ones who survive are not necessarily the strongest. It might be the quickest, smartest, darkest skinned, one with most body fat stored up, or whatever.
That's the problem. We (in the distant past) don't know what conditions are coming to where we are, or what conditions we will encounter when we move.
In most traits there is a range of variation. There are hundreds or thousands of traits. Some are visible (skin color), some are genetic (resistance to particular diseases). Some individuals are better able to survive and pass on their genes. The differences are often tiny, fractions of a percent, but with lots of time they can add up.
In time, the range of variation shifts toward one end or the other. When people migrated out of Africa and toward the northern end of Europe, skin color lightened. In Africa selection pressure favored protection from intense ultraviolet radiation, and dark skin was necessary. In northern Europe selection pressure favored vitamin D production, and the skin had to be lighter to pass the correct amount of ultraviolet radiation for vitamin D production. There is a cline, or range of variation between Africa and northern Europe, with skin color becoming lighter as you go north.
The mechanism for this is natural selection in favor of those who are best suited for a region.
It is very complex, with lots of traits involved. We study the results using current populations as well as fossils. We have a lot to learn, but there is a lot that has already been discovered.
Evolution applies to populations, not individuals. A very simplified desctiption would be to notice that any population is slightly different from its parent population (this difference maybe due to mutations, crossing over, or other genetic happening.) Not all individuals in a population have the same number of offspring in the daughter population; this can be due to strength, speed, beauty, wealth, luck, weather, etc. Thus the frequency distribution of genetic material changes between each generation. (Generations may overlap.)
That's all there is to evolutionary theory. Any system which undergoes inexact replication will undergo Darwinian evolution. All that is necessary is inexactness in replication and/or members of the system being in different environments even if only slightly.