How Bison Could Hold the Key to Human Migration

The precise timing and movements of people between North America and Asia is a hodgepodge of guesswork and conjecture that seems to have new updates every few years. Much of the discussion involves the Bering Land Bridge, which for a time connected Alaska with Russia: When did people traverse this? Which paths did they take? Which people did the traversing? From where did they come – existing early North Americans moving north into Russia, or early Asians moving south into North America?

A new pair of studies asks similar questions, but draws very different conclusions from them, which is to be expected when we’re talking about minimal data used to learn about the movement of people 14,000 years ago.

The New York Times dives into this pair of studies, but they’re still not easy to parse. Here are the basics: Around 23,000 years ago, anyone who found themselves wanting to move south from Alaska would have encountered a gigantic, impassible glacier spanning most of what is now western Canada. This would have included anyone from Russia, who crossed the Land Bridge only to run headlong into ice, as well as anyone from the interior of North America wanting to make the reverse journey.

At some point, a crack developed in that glacier, running roughly north-south through what is now Alberta and British Columbia. This crack is known as the “ice-free corridor,” and would have allowed the free passage of humans through it, thus finally and truly connecting North America with Alaska. But when that exactly happened is the present question.

Here’s where bison come in: The crack developed after enough time that populations of bison, separated by the glacier, became different, deep down in their DNA. This took around 10,000 years, which is not that long, geologically; the differences between these bison populations are accordingly minuscule. They were thus separated into the Alaskan bison, north of the glacier, and the interior North American bison, south of the glacier.

One study, from the University of California, Santa Cruz, studied the remains of bison found along the ice-free corridor for those tiny differences, trying to find when the Alaskan bison moved south and the interior North American bison moved north. By comparing this data – they dated the presence of, say, Alaskan bison DNA in the southern part of the corridor, and the North American bison DNA in the northern part – the team concluded that the ice-free corridor was open for business around 13,000 years ago.

It’s believed that no human could have made this journey without the aid of the bison.

The second study, this one from the University of Copenhagen, analyzed sediment from the modern-day area where the ice-free corridor once stood. (The melting of the glacier in that area formed a big lake which slowly drained, leaving a few smaller lakes behind. The sediment examined was found in lakes thought to be remnants of that initial big lake.) That second team’s conclusion is similar, but not identical: They place the opening of the ice-free corridor about 500 years later than the first team’s estimate.

Why this all matters is because of the vast importance that the ice-free corridor has on the settlement of North America. Exactly when bison roamed through the 900-mile-long ice-free corridor is vital; it’s believed that no human could have made this journey without the aid of the bison. Being a recently thawed glacier, there wasn’t much food in the ice-free corridor – but once the bison enter it, there’s plenty of meat to sustain the settlers.

Now we come to the Clovis people, understood to be the primary ancestors of American Indians. That 500 years makes a big difference: By the estimation of the first group of scientists, the timing is perfect for the ice-free corridor to have been a primary route for immigration from Alaska. By the estimation of the second group? It’d be too late; the second group believes that the Clovis people were already pretty well situated in interior North America by that point, meaning that they must have found some other way to get here.

There are no conclusions in the study; these two groups disagree even while seeming to come awfully close to agreeing on the timeline. But what both groups believe is something far more basic: Migration would not have been possible without the bison. The movement of the bison is entangled with the movement of humans in ways that can never be untangled.

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