We finally found the genetic 'knob' that lets dolphins sleep with half their brain at a time.
April 15, 2026
Original Paper
Selection on PER2 phosphorylation regulation underlies atypical mammalian circadian rhythms
SSRN · 6578345
The Takeaway
Imagine being able to shut down half your brain to nap while the other half stays alert for predators—that’s the dolphin superpower. Scientists have finally identified the exact genetic mutation that makes this possible. By tweaking how a specific protein (PER2) is modified, evolution allowed dolphins to maintain a unique biological rhythm that supports 'unihemispheric' sleep. This discovery isn't just about dolphins; it helps us understand the fundamental limits of our own sleep-wake cycles. It shows that sleep isn't an all-or-nothing state, but something that can be genetically 'partitioned' if the stakes are high enough. We're finally understanding the biology of a brain that never truly turns off.
From the abstract
The circadian rhythm enhances survival and fitness, but some species show weakened or absent rhythms, reflecting adaptations to extreme environments. The genetic basis remains unclear. Here, we examined 20 PER2-associated genes across 71 mammals. Four genes showed positive selection in atypical circadian lineages, three of which (CDK5, CSNK1E, GSK3B) participate in PER2 phosphorylation. Notably, CSNK1E, a key kinase for PER2, exhibited positive selection and accelerated evolution in cetaceans th