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Comment by ink_13 | Hacker News Reader

"Soon" on an evolutionary scale could still mean hundreds if not thousands of years.

For example, wood is a great food resource for fungi, but it took millions of years for wood-eating fungi to evolve after wood.

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It's complicated! My bet would be less on individual species slowly adapting, and more on mass extinction and re-specialization.

When there's a big shock, specialists have a harder time, and generalist species have an edge. So, when an ecosystem is destabilized or totally transformed, generalists tend to take over. The thing about generalists is that they adapt to new environments quickly. Once they live stably in a new environment long enough, they begin to adapt to it more stably, and specialize, leading to new speciation.

Songbirds are a great example of this; they exploded out of Australia some 40 million years ago, spread everywhere, and then specialized like crazy into their new environments. They likely out-competed a lot of pre-existing local species as they spread out. Humans are also a great example - we spread everywhere as successful generalists, and started the process of biologically specializing in our new environments without fully speciating. In the case of humans, we know pretty precisely about the wave of megafauna extinctions that accompanied our spread.

The Younger Dryas megafauna extinctions cannot necessarily be attributed to humans. Humans spread tens of thousands of years ago. And numerous megafauna still exist in Africa, the likely birth place of humanity.

What are the alternative hypothesis?

There aren't any unless you're an incredibly fringe academic or using dumb terminology to avoid admitting that strong multiregionalism is entirely dead. Human evolution didn't stop there and there are unresolved questions about where within Africa different phases of the process occurred, of course, but the continent as a whole is undoubtedly where anatomically modern humans emerged.

There's an impact meteor hypothesis, disease, super volcano, and the rapid seesaw climate change itself.

https://blogs.scientificamerican.com/history-of-geology/http...

Well... lots more here. My impression was that African mammals survived in part because they co-evolved with humanity, and didn't get quite the shock as other places where humans showed up fully formed.

https://en.wikipedia.org/wiki/Holocene_extinction#Historic_e...

Wild mammal biomass is estimated to be about 83% lower due to humans. Reduction in biomass isn't exactly synonymous with extinction, but they aren't totally unrelated either.

https://www.theguardian.com/environment/2018/may/21/human-ra...

Yep. I remember being blown away when I learned that most early trees fossilized because there was nothing yet to break them down. Not fungi, not bacteria, not insects.

Pretty crazy to imagine. large swaths of land with layers and layers of fallen trees

Most of them would have broken down, it's not like giant piles of logs. Think more "heavily wooded bog"

The weather still breaks down dead plant matter, even without fungi or insects, I think?

Yes, it turned to mud, then oil.

If there was oxygen, it still burned. One lightning strike would be enough to wipe the ground clean.

There was much less oxygen back then.

This was the Carboniferous age when oxygen levels are thought to have been up to 35% as opposed to 21% now.

Most trees probably grew in swampy areas and the water they fell into would have been lower in oxygen. The material would have built up in the water and mud.

The evolutionary lag hypothesis is trivially false. Simple calculations show you’d quickly run out of atmospheric carbon.

So, can you provide the calculations?

I mean, we did?

Atmospheric CO2 levels in the pre-tree era 400 Myears ago was something like above 6000ppm, compared to 280ppm in the pre-industrial era. Even burning coal formed during this time like mad, 90% of the atmospheric CO2 is still just gone.

Could mean a long time, or could not. There have been new bacteria/fungi discovered around chernobyl which subsist on gamma radiation. It's not like evolution of new processes are guaranteed to happen slowly, it just seems unlikely to happen quickly.

https://en.wikipedia.org/wiki/Radiotrophic_fungus

Many of the photosynthesizing algae can complete a lifecycle in 8 hours. They should be able to evolve pretty quick to new conditions, especially across the huge volume of ocean water.

Trees and stuff will be far slower, yes.

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