I think its testable. There's several parts. 1. Its clearly testable whether or not the phase of the circadian rhythm of humans shifts with age. 2. Having a

I think its testable. There's several parts. 1. Its clearly testable whether or not the phase of the circadian rhythm of humans shifts with age. 2. Having a range of circadian rhythm phases in your pack is useful for a 24-hour watch by definition, but in order for it to have been an evolutionary factor, watches that take advantage of this would have to actually happen in the wild. Finding wild packs of humans is a tall order, but if #1 holds for other primates or even other pack mammals, you could measure to what extent packs operate their 24-hour watch with different age groups at different times of the day. 3. The final price needed is to show that having a more alert watch gives a better survival rate. That seems self-evident, but it could also be tested by monitoring wild packs of humans or other primates.