One of my cousins is married to an archaeologist who is a paleo-indian expert. He worked at Museo Archaeologico de Mexico for many years before taking a job stateside at a university.
He supervised a lot of neat digs at sites in Mexico, and always invited us to visit them-since my family is Hispanic, I found it particularly fascinating, and have ever since.
He was talking about the politically incorrect theory of well-traveled far ancestors who sailed, traded and mated all over the world long before any land bridges or empires came to be. Many of his collegues thought he was nuts-he is laughing his ass off now every time he is vindicated.
Sounds like your cousin's husband would be a kindred spirit to the old professor I studied under. His name was Edward Milligan and he had been adopted into the Dakota tribe. He published under the title Historic Migration of North American Indian Tribes and his work was largely pooh-poohed by the experts, many of them for allegedly superficial reasons like Prof. Milligan's imperfect grammar in writing.
His most memorable statement was squarely aimed against some of his critics who still contend all original Native American migration was over the Bering Strait land bridge. The Prof. pointed out that every other civilization built their greatest cities near where they first entered the continent, then more rudimentary dwellings as they moved further away. "Why," asked the professor, "should only America be the opposite?" The greatest evidence of civilization are concentrated between Peru and Central Mexico. Northern Mexico and the American southwest still have some fairly impressive but less developed evidence of civilization. But as you move into Northern California and up the Pacific Northwest to the Bering Straight, evidence of even rudimentary civilizations grow even more sparse. You can't dismiss it by climate alone because at least the southern portion of the Pacific Northwest has a climate far milder than the mountains of Peru where these ancient people thrived.