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The expansion of modern humans ~50,000 as part of a regular Poisson process

Last of the giants: What killed off Madagascar’s megafauna a thousand years ago?:

The first job is to understand exactly when the megafauna died out.

Radiocarbon dating of over 400 recent fossils demonstrates that animals under 22 pounds lived on Madagascar throughout the last 10,000 years. For animals over 22 pounds, there are abundant fossils up to 1,000 years ago, but relatively few since. The biggest decline in number of large animals occurred rapidly between A.D. 700 and 1000 – practically instantaneous given the long history of their existence on the island.

According to new dates on fossil bones with cut marks on them, humans arrived on Madagascar 10,500 years ago, much earlier than previously believed. But whoever these early people were, there’s no genetic evidence of them left on the island. New analysis of the human genetic diversity in modern Madagascar suggests the current population derives primarily from two waves of migration: first from Indonesia 3,000 to 2,000 years ago, and later from mainland Africa 1,500 years ago.

So it seems that people lived alongside the megafauna for thousands of years. How did the humans interact with the large animals?

Our new study found dozens of fossils with butchery marks. Cut and chop marks provide compelling evidence as to which species people were hunting and eating. Evidence of butchery of animals that are now extinct continues right up to the time of the megafaunal crash. Some people on Madagascar hunted and ate the megafauna for millennia without a population crash.

The abrupt land use change might hold some clues. The transition from a forest-dominated ecosystem to a grassland-dominated ecosystem appears to be widespread….

This research about Madagascar is important. If it turns out correct, I think it gives us deep insights about the expansion of modern humans outside of Africa ~50,000 years ago, and why their arrival resulted in the extinction of so many other human lineages. A generation ago we might have posited that some massive bio-behavioral change is what triggered this, but I am coming closer to the idea that cultural changes are punctuated enough that that may actually explain things. The culture changes first, then genes follow the culture.

Perhaps one might posit a model with massive turnovers in the hominin lineage due to this cultural dynamic occurs periodically, as if it’s a Poisson process.

4 thoughts on “The expansion of modern humans ~50,000 as part of a regular Poisson process

  1. “In fact, the sequential extirpation of giant Megalochelys tortoises from various islands in the Indo-Australian Archipelago during the Pleistocene is generally interpreted as a specifc indicator for the migratory arrival of early hominins, Homo erectus, gradually spreading across the Archipelago (Sondaar 1981, 1987; van den Bergh 1999; van den Bergh et al. 2009). All continental taxa of giant Megalochelys tortoises in the Sivaliks of India went extinct by the Early Pleistocene, and insular taxa also went gradually extinct in most of the Archipelago, surviving into the Middle Pleistocene only on Timor. By the Late Pleistocene, there were evidently no more giant tortoises anywhere in the South Asia and Southeast Asia regions.”

    https://www.researchgate.net/publication/275040990_Turtles_and_Tortoises_of_the_World_During_the_Rise_and_Global_Spread_of_Humanity_First_Checklist_and_Review_of_Extinct_Pleistocene_and_Holocene_Chelonians

    Madagascar had giant tortoises until the the Austronesians arrived. Same species as Aldabara Island. Surprisingly giant tortoises aren’t a case of island gigantism–they had to get big first to survive bobbing in the waves for weeks. Their mainland forebears were possibly the first thing humans wiped out. It’s hard to imagine modern humans living side-by-side with them for millennia. Is it possible Madagascar has the same radiocarbon dating issues Polynesia did until an exhaustive review in 2011 gave them a NET date of 1100 or so?

  2. My theory – usually hunters don’t wipe out species (this will go against their enlightened self-interest – destroying their food source), farmers do.

    Btw, not much different from what occur in natural ecosystems (where, I think, extinction is more common from competition than from predation).

  3. @Miguel, interesting idea; I’d guess hunters do, but only if they have an alternate prey species to fall back on, or out of desperation (and then they have to migrate out or die).

    Plus you’ve got the element of competition as you say – hunters might not slay all the elk so that they have a continued food source, but it’s difficult to see why they wouldn’t try to slay every wolf they come across, or more likely, drive them to starvation or cooperative-domestication, with survivors being generally smaller predators that target prey that humans find uneconomical to hunt.

    Natural ecosystems are a difficult analogy as well, I’d guess, as humans (Sapiens) are a cosmopolitan invasive where we’re generally found, so not so much co-evolution of predator:prey.

    Re; farmers that may depend on niche competition. Lots of early farmers seem to have pretty narrow niches for cultivation (particular soils, local climates) and might impact land outside those niches less than hunters. That might be what happens in Madagascar. Early Austronesian and African farmers shifting to more widespread cultivation outside niches?

  4. Hunters might not *intend* to wipe out a prey species, but when a famine hits and it’s a choice between your children starving and violating an over-hunting taboo….

    Also, the hunters do not necessarily have a good idea of the factors determining prey abundance (heck, we still don’t in a lot of cases even today). They may believe that the tortoise shortage is due to Thog’s wife offending the Master of Game by looking at the sacred drum while menstruating or something.

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