It would require conditions where those who are better adapted to higher temperature produce more offspring than those who aren't, consistently over many genera

It would require conditions where those who are better adapted to higher temperature produce more offspring than those who aren't, consistently over many generations. The Nepalese would have developed this change over thousands, if not tens of thousand of years. The climate crisis is likely to come to a burning head in the next hundred. In all likelihood, we'll use technology to circumnavigate the issue and it will never get to the point where humans are put into a position where adaptation occurs.