"More recent research has shown that there were evolutionary events millions of years ago that caused this divergence. They were random events and they're not, as you might imagine, likely to happen again in any reasonable time scale. Once those fish are gone, their genotype is gone". Samatha Kannry talks about pre-mature migrating fish like spring chinook and summer steelhead, how their genetic variance evolved, and why they are more vulnerable to human induced changes to habitat than their