Matching the body’s internal clock to the environment is needed for best survival in natural populations

Fitness, measured as the expectation of future offspring, is maximized in environments that align with the period of an organism's circadian clock.

• Organisms with circadian clocks exhibit better fitness when their internal timing aligns with environmental cycles.
• The study directly tests the relationship between circadian clock period and fitness outcomes.
• Temporal concordance between internal clocks and external environments is essential for maximizing reproductive success.
• Findings support the idea that circadian clocks have an adaptive function in eukaryotic organisms.

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