[plasticeagle]

It's a very common misconception that "survival of the fittest" means something related to physical fitness or stamina. It does not, in fact it's almost tautological. It means only "survival of those most likely to survive."

Natural selection is still fully in operation, but the things being selected for may have changed. Whatever they are now, they are still being selected for. Those most likely to reproduce are those whose who reproduce the most, and whatever those characteristics are, they will be the ones that become more prevalent.

It's also very important to remember that this operates over hundreds of millennia. Human beings changing substantially will not occur within a period of time less than that. You'd need to look back into deep prehistory to find changes to humans attributable to natural selection. Changes to modern humans are all explicable through changes to nutrition and lifestyle, not through evolution.

[killerstorm]

Well, modern medicine + economy + social pressure resulted in RADICAL change in fitness function for human population. It's very, very different.

So it's quite likely that modern population is not fit according to old criteria.

> It's also very important to remember that this operates over hundreds of millennia.

That's not true at all. People can make new breeds of dogs and cats in just a few generations. You can literally SEE how a change of fitness function affects the phenotype.

> You'd need to look back into deep prehistory to find changes to humans attributable to natural selection.

There are many studies which describe genetic changes within latest 10,000 years or less. E.g. paper "1,000 ancient genomes uncover 10,000 years of natural selection in Europe": "We identified 25 genetic loci with rapid changes 21 in frequency during these periods". You can find many similar papers if you do a search

One of studies identified changes in loci associated with Y. pestis immunity during the Black Death (i.e. something like a century). Black Death mortality is similar in scale to early childhood mortality 150 years ago.

[plasticeagle]

I suppose that must depend on one's definition of "substantially". Human's haven't changed "substantially", and neither do new breeds of dogs and cats.

Besides which, why does it matter that Humans may or may not be fit according to old criteria? Whatever they might have been.

[killerstorm]

People in the past could survive and procreate without modern medicine (basically without any medicine at all as doctors could do very little 200 years ago) with ~50% success rate. I'd suspect this rate is already lower now, and it might matter in multiple ways

[throwaway173738]

“survival of the fittest” was actually coined by a political economist, Herbert Spencer, to explain how lassiez-faire economics produces better companies. Darwin didn’t extrapolate to that in his theories and the quote is often applied to explain how evolution works, but that may not be the case. We can say that evolution results in change but that there are no guarantees that those changes result in fitness of the organism. We can only say that sometimes they obviously do and in other cases we can make up “just-so” stories to explain stuff in terms of fitness.