bio

Free-running period

The cycle length an organism's internal clock keeps when it is cut off from every external time cue - no light, no clocks, no dawn. Usually written as tau. The striking thing is that it is almost never exactly 24 hours: humans drift at about 24.2, fruit flies and hamsters near 24, the fungus *Neurospora* around 22, the sensitive plant around 22.5. That small wrongness is not a defect but the design - a clock that needs correcting daily is a clock checked against reality daily, so it stays flexible as the seasons shift instead of rigid.