We evolved on Earth, with regular 24-hour “circadian” cycles; abandoning them is incompatible with survival. Natural Selection does not look upon this favorably.
Natural selection against a circadian clock gene mutation in mice (Spoelstra et al., 2016)
resulting in significantly increased predation in the wild:
In the current study, there was a somewhat “weaker” circadian disruption: the mice expressed a mutant casein kinase 1 resulting in a shorter circadian period.
But this similarly negatively impacted net survival.
In contrast to complete SCN ablation, where the mice were predated more, this study followed more aspects like lifespan, suvivorship, births, etc., (ie, more holistic “natural selection,” I think) in cool outdoor enclosures that looked like this:
All animals had little implants which monitored activity and the amount of times they entered the feeder, and were pronounced deceased if they stopped entering the feeder.
Interestingly, mice with a Period2 deletion, which induces internal circadian disruption but does not impact actual circadian period, does not impact natural selection. No doubt, internal circadian arrhythmia predisposes humans to a plethora of disease conditions (eg, cancer), but the 24-hour period length must be maintained.
We evolved on Earth, with constant 24 hour LIGHT/DARK cycles; abandoning them is incompatible with survival. Natural Selection does not look upon this favorably.