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Comment by __cxa_throw | Hacker News Reader

What is the new widely accepted theory for how humans first arrived in the Americas, if not for the traditional Bering Land Bridge hypothesis?

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The new theory is that they came along the coast. Clovis culture arrived 13-16,000 years ago through corridor in ice sheets. But earlier sites, including these footprints, suggest that people arrived another way. These footprints are 21-23,000 years ago. I don't think there is any evidence how they got there, but the coast is plausible explanation.

When you say "the coast", do you mean travelling south down the Pacific coast after crossing the Bering land bridge?

Edit: ah, the earlier discussion covers this: https://news.ycombinator.com/item?id=44319585

There is genetic evidence linking these very old inhabitants to Pacific Islanders of that time and there were more islands at that time because of lower sea levels.

It's really confusing to use the term pacific islanders here. The farthest humans had reached was the Solomon Islands, what we call "near Oceania". The places people think of when they say "Pacific Islands", namely Remote Oceania (Melanesia), Micronesia, and Polynesia were all uninhabited. Those early Papuans weren't especially closely related to the founding populations of the Americas, though they're closer than you might expect from the geographic distance because of the serial founder effect.

Yes, that is a really extreme simplification. There were at least three major groups of early humans around Southeast Asia and the Pacific Islands 20k+ years ago. The main point of interest is that all of these groups were genetically differentiated from the Siberians who migrated along the vicinity of the Alaskan coast later and who left a genetic trace on native populations that is still observable today.

There is also evidence that pacific Islanders made at least two trips to the Americas using rafts.

I believe generic testing shows pacific Islander and early Asian DNA mixing.

Stefan Milo on YouTube has a few videos looking into different theories.

The Pacific Islanders didn’t get to Tahiti and Hawaii until 1000AD.

My lay understanding is that the theory is that these earlier humans crossed the Bering land bridge but that they didn't proceed through a inland ice-free corridor (as there was none then). They likely traversed the pacific coast, which was not at the same position it is today and so would leave no evidence.

I have also seen discussion of sea arrivals, but they are much more hypothetical.

Also worth noting as the earlier arrival doesn't rule out the later ice-free corridor traversal as having also happens - it just means it wasn't the first people to arrive in the Americas.

It's not that different. There's just dispute over when exactly between 30kya and 11kya people first crossed.

In addition to what other people have indicated, there's a long tale of competing theories. There's very limited evidence of human settlement in the old crow flats as far back as 40kya (which is still 20kya after the settlement of australia), but unfortunately this evidence (butchered animal bones) are circumstantial and the dating is not reliable.

However, i think ~23kya is a pretty safe bet at this point. And there are dozens of sites before 14kya as far south as chile. Clovis first has been largely rejected for about 30 years now but the old narratives keep floating around.

I like the Battlestar Galactica theory for this - a group of humans and human-Cylon hybrids bred with the early Neanderthals in different regions of the world.

To put it bluntly, we don't have a good theories to explain the white sands timeline.

There have been a few major explanations that overlap in parts:

1) The Ice-Free Corridor, which was closed from 26-14ka. This is the old, traditional theory from the 50s-60s. It survived the widespread recognition of pre-clovis cultures with sites like Monte Verde (~13ka) because the dates hadn't been refined to where they are today. It's been considered dead for awhile now though, but potentially up for a resurrection with how far back the white sands dates are.

2) Pacific Coastal Migration Hypothesis. Around 30-25ka, coastal foragers from somewhere between Japan and Kamchatka migrated east along the Alaskan coast, living off a combination of terrestrial and marine resources in the relatively mild climate of the coast. This assumes the existence of ice free coastal refugia where people, animals, and plants were able to live during the last glacial maximum (LGM). So far, we have little to no evidence to suggest that these existed. More work needed to understand fine-scale glaciation of the Alaskan coast during the LGM. Additionally, the Alaskan current is thought to have been extremely strong during this period, potentially impossible to sail against. Again, better climate modeling needed. This is the de-facto explanation because we don't have anything better, but it's not something anyone's happy with.

3) Beringia standstill Hypothesis. Usually seen in combination with one of the previous two, but the idea is that humans inhabited inland Beringia until relatively recently and then proceeded into the subarctic Americas by one of the other routes. This works well with the genetic data, but the IFC hypothesis is basically dead and it excludes the earlier entry. The later date doesn't work with preclovis archaeology. Access to the pacific coastal route seems to be prevented by glaciation along the southern alaskan coast until later than the genetic data would indicate, so this not a well-explored hypothesis. Better climate modeling needed.

4) The kelp highway hypothesis. Basically similar to the coastal migration hypothesis, with less emphasis on terrestrial resource use. It has many of the same problems and you'll sometimes see people group them together with a term like "Pacific Coastal Route". The society this hypothesis requires doesn't look like any culture we've observed anthropologically. It's not especially compatible with available genetic data (though this can be somewhat explained). It's not well supported by archaeological evidence, either. It's not widely discussed on its own.

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