How does natural selection work? Especially now, in the modern world. How does nature select stuff? How random is it?
Basically, natural selection can be explained by superior reproductive success primarily due to heritable traits. In a nutshell.
Since people have more than one child, there would be an unlimited exponential growth of the human population. But that’s not sustainable. All natural resources (food, space, water, gas) are limited, so population growth will most definitely hit a wall.
It’s not about “survival of the fittest”, but about reproductive success. So who’s the best at reproducing will have a higher chance of contributing to the next generation. And the successful genes will be transmitted this way over generations.
The best explanation I read came from Richard Dawkins who took Darwin’s theory and rewrote it in laymen’s terms including what we know now about genetics. You’ll find all this in his book The Selfish Gene.
He says all humans have a number of genes in common, but not all which is what makes us all different. Every difference which manifests itself as an advantage favours survival and reproduction. These are the differences that will spread and often increase over generations.