There are people with more or less sensitive GLP-1 receptors today, who have lesser or greater impulsivity. If some event occurs where only those with lower impulsivity survive, then the future population will have more sensitive GLP-1 receptors.
This is the only way that happen - noticeable evolution is always driven by population bottlenecks or strong selective pressure. In the absence of those, mutation just keeps expanding the gene pool so more different candidates are available for the next bottleneck.
In case an event happens where only red-haired people survive, good thing some are available, otherwise there's no reason to think everyone will have red hair in the future.
This is the only way that happen - noticeable evolution is always driven by population bottlenecks or strong selective pressure. In the absence of those, mutation just keeps expanding the gene pool so more different candidates are available for the next bottleneck.
In case an event happens where only red-haired people survive, good thing some are available, otherwise there's no reason to think everyone will have red hair in the future.