You're right that it is a relatively recent development: the first papers (cautiously) going against this idea of evolution happening slowly started appearing in the middle of the last century. The first paper flat-out stating evolution was observed within a few generations was in the late 1970s (mentioned in the linked article in my previous post). So you can imagine it would take a while for the field to accept this new attitude, let alone how long it takes for this new knowledge to then diffuse into the rest of society.

Either way my comment certainly wasn't intended as a critique aimed at you!

Also, thinking about it some more, it's not that strange that the idea of slow evolution hasn't died out yet, because it's not so much wrong as that reality more complicated and really counter-intuitive than what you think if you only look at fossils[0]:

> In the 1950s, the Finnish biologist Björn Kurtén noticed something unusual in the fossilized horses he was studying. When he compared the shapes of the bones of species separated by only a few generations, he could detect lots of small but significant changes. Horse species separated by millions of years, however, showed far fewer differences in their morphology. Subsequent studies over the next half century found similar effects — organisms appeared to evolve more quickly when biologists tracked them over shorter timescales.

> Then, in the mid-2000s, Simon Ho, an evolutionary biologist at the University of Sydney, encountered a similar phenomenon in the genomes he was analyzing. When he calculated how quickly DNA mutations accumulated in birds and primates over just a few thousand years, Ho found the genomes chock-full of small mutations. This indicated a briskly ticking evolutionary clock. But when he zoomed out and compared DNA sequences separated by millions of years, he found something very different. The evolutionary clock had slowed to a crawl.

(I have to apologise for not remembering this article yesterday, it would have made things more clear)

So in retrospect my "very stubborn idea" assessment is probably a bit unfair.

But, back to what we were taught in school. Caveat: I'm not a biologist, let alone evolution expert, just a nerd who is into this topic. There are a number of issues with the description you gave (which, for the record, fits with how it was taught to me in high-school)

It is true that evolution is not linear, but being taught that evolution is a stair step is just as bad. It (implicitly) assumes evolution is a form of progress. It's not, it's just adaptation. The simplest of life forms that exist nowadays are just as successful as we are, in the sense that they also didn't go extinct and will continue to thrive in the future. On the other end of the spectrum you actually can have runaway adaptation, especially when there's a kind of "arms race" between predator and prey. The cheetah is so hyper-specialised for catching its prey by speed alone that it's a kind of evolutionary dead-end; it can't zig-zag like the gazelle can. Anyway, the stair-step attitude originates from outside of biology, from Platonic thinking that there are "higher" ideal forms.

And the sudden changes turn out not to be "few and far between", they just don't seem to stick. Most adaptations average out, because they're highly contextual to their short time periods. As mentioned, since we based our first ideas about evolution on fossils, we only noticed the slow evolution. Sex actually seems to play a large part in the filtering process[1]:

> For a species whose numbers show no signs of collapsing, humans have a shockingly high mutation rate. Each of us is born with about 70 new genetic errors that our parents did not have. That’s much more than a slime mold, say, or a bacterium. Mutations are likely to decrease an organism’s fitness, and an avalanche like this every generation could be deadly to our species. The fact that we haven’t gone extinct suggests that over the long term, we have some way of taking out our genetic garbage. And a new paper, recently published in Science, provides evidence that the answer may be linked to another fascinating procedure: sex. (...) As the number of nasty genetic errors in a population rises, natural selection will sweep large rafts of them out of the genome together. And in sexual organisms, because of the ways that mutations from each parent can recombine randomly onto the same chromosomes, the synergistic elimination of bad mutations can happen even faster.

Anyway, hope this addresses some of your understandable scepticism!

[0] https://www.quantamagazine.org/evolution-runs-faster-on-shor...

[1] https://www.quantamagazine.org/missing-mutations-suggest-a-r...