Dr. David Gwynn

Or they have to wait until after the ice sheets begin to melt. Because when the ice sheets begin to melt as the world is warming at the end of the ice age, you've got a couple of routes that will open up that will take you from that cul-de-sac where you've been parked for however many centuries or millennia down into what we refer to here in the States as the lower 48, right? The lower 48 states.

One of those routes is along the Pacific coast and it appears to be ice free starting around 17,000 years ago, but probably for sure by around 16,000 years ago. And then there's the so-called ice free corridor, which opens when the Laurentide and the Cordilleran ice sheets begin to melt and there opens between them.

One of those routes is along the Pacific coast and it appears to be ice free starting around 17,000 years ago, but probably for sure by around 16,000 years ago. And then there's the so-called ice free corridor, which opens when the Laurentide and the Cordilleran ice sheets begin to melt and there opens between them.

One of those routes is along the Pacific coast and it appears to be ice free starting around 17,000 years ago, but probably for sure by around 16,000 years ago. And then there's the so-called ice free corridor, which opens when the Laurentide and the Cordilleran ice sheets begin to melt and there opens between them.

an unglaciated route down to the south, an unglaciated corridor down to the south. This is like a corridor, isn't it? A narrow route almost.

an unglaciated route down to the south, an unglaciated corridor down to the south. This is like a corridor, isn't it? A narrow route almost.

an unglaciated route down to the south, an unglaciated corridor down to the south. This is like a corridor, isn't it? A narrow route almost.

The width of the route obviously grows over time and it opens in kind of a funny way. You know those winter coats that we wear that have a zipper that zips up from the bottom and zips down from the top? Well, this was the ice-free corridor. So it opens, it's pretty wide at the top, it's pretty wide at the bottom. And then in the middle, it still hasn't quite opened up yet.

The width of the route obviously grows over time and it opens in kind of a funny way. You know those winter coats that we wear that have a zipper that zips up from the bottom and zips down from the top? Well, this was the ice-free corridor. So it opens, it's pretty wide at the top, it's pretty wide at the bottom. And then in the middle, it still hasn't quite opened up yet.

The width of the route obviously grows over time and it opens in kind of a funny way. You know those winter coats that we wear that have a zipper that zips up from the bottom and zips down from the top? Well, this was the ice-free corridor. So it opens, it's pretty wide at the top, it's pretty wide at the bottom. And then in the middle, it still hasn't quite opened up yet.

So people basically have to wait for the whole thing to be open. But, and this is an important point, and this is something that we found with ancient environmental DNA, just because the corridor is open doesn't mean it's a passage. Because when the ice retreats, you've got nothing there yet. at least immediately after the ice retreats, except mud water flats, lakes, nothing's growing there.

So people basically have to wait for the whole thing to be open. But, and this is an important point, and this is something that we found with ancient environmental DNA, just because the corridor is open doesn't mean it's a passage. Because when the ice retreats, you've got nothing there yet. at least immediately after the ice retreats, except mud water flats, lakes, nothing's growing there.

So people basically have to wait for the whole thing to be open. But, and this is an important point, and this is something that we found with ancient environmental DNA, just because the corridor is open doesn't mean it's a passage. Because when the ice retreats, you've got nothing there yet. at least immediately after the ice retreats, except mud water flats, lakes, nothing's growing there.

And so at the end of the Pleistocene, when the corridor opens up, you can't pack a lunch in Fairbanks and say, you know, if I'm really careful and I don't eat too much on the first day and the second day, I can make that thousand kilometer trek with my sack lunch.

And so at the end of the Pleistocene, when the corridor opens up, you can't pack a lunch in Fairbanks and say, you know, if I'm really careful and I don't eat too much on the first day and the second day, I can make that thousand kilometer trek with my sack lunch.

And so at the end of the Pleistocene, when the corridor opens up, you can't pack a lunch in Fairbanks and say, you know, if I'm really careful and I don't eat too much on the first day and the second day, I can make that thousand kilometer trek with my sack lunch.

No, you've got to wait for animals and well, you've got to wait for plants and then animals to basically make that corridor biologically viable. You've got to have something to eat in there, right? And so...

No, you've got to wait for animals and well, you've got to wait for plants and then animals to basically make that corridor biologically viable. You've got to have something to eat in there, right? And so...

No, you've got to wait for animals and well, you've got to wait for plants and then animals to basically make that corridor biologically viable. You've got to have something to eat in there, right? And so...

One of the things that we found, and this is again work with Willerslev's group, in particular Mikkel Pedersen, who's one of the sort of specialists in that group on ancient environmental DNA, we had cores from that center of the zipper, as it were. It was one of the last places within that corridor to open up. And what we found was that, again,