I seem to hear from a variety of people that they struggle to fall asleep at night; but the difficult to fall asleep sounds like an evolutionary downside. Even as hunter-gatherers, being able to sleep whenever and wherever sounds like it would be an advantage.

Is it a recent product of modern times and people didn’t actually struggle with it a while back? In which case, what of modern life is causing this? If not, what is the evolutionary advantage of not falling asleep easily?