bio

Nocturnal bottleneck

The hypothesis that ancestral mammals spent something over a hundred million years confined to the night shift, because the day shift was fully staffed by dinosaurs - and that this long exile is why mammals are built the way we are. The evidence is our own sensory legacy: most mammals lost two of the four colour-detecting pigments their ancestors had, which is why a bird or a lizard sees a richer world of colour than nearly any mammal - colour is expensive and useless in the dark, so it was allowed to go. In exchange, whiskers, hearing and smell were elaborated far past what a daylight animal would need. Human colour vision is a partial re-acquisition, a later patch on an animal built for the dark. The hypothesis is still argued over: fossil eye sockets suggest some Mesozoic mammals were out in the daylight after all.