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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, spec
by sdenton4 3y ago
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.
- chrisco255 3y agoThe 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.
- brutusborn 3y agoWhat are the alternative hypothesis?
- AlotOfReading 3y agoThere 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.
- chrisco255 3y agoThere's an impact meteor hypothesis, disease, super volcano, and the rapid seesaw climate change itself. https://blogs.scientificamerican.com/history-of-geology/httpblogsscientificamericancomhistory-of-geology20110727the-younger-dryas-impact-hypothesis/ https://blogs.scientificamerican.com/history-of-geology/http...
- sdenton4 3y agoWell... 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_extinction 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-race-just-001-of-all-life-but-has-destroyed-over-80-of-wild-mammals-study https://www.theguardian.com/environment/2018/may/21/human-ra...