Glossary

Nocturnal bottleneck hypothesis

Defined in topic 1

Gordon Walls's 1942 argument that mammals passed through a nocturnal phase costing them visual equipment reptiles and birds still carry. Shared gene losses support the phase; the dinosaur explanation is less secure.

Published 22 September 2026Updated 22 September 2026

Where this comes from

Reference topic 1The 200-Million-Year Warm-UpThe mammalian operating system: warm blood, night-built senses, milk, late-added color vision.

In the reference topic that owns this term

Reference topic 1, The 200-Million-Year Warm-Up, states the mismatch as a card: what the system evolved to expect, what it gets instead, and what happens in the gap.

Mismatch card

What it expects: High energy costs paid for by effortful foraging; real darkness at night; changing temperatures; food judged by color and smell.
What it gets: Abundant calories, climate-controlled rooms, bright evenings, engineered food colors.
What happens in the gap: Sleep and light (Topic 23), temperature (Topic 25), food reward (Topic 11); even the body's thermostat is drifting, for unknown reasons.

The full card, and the topic behind it

Related terms

The argument behind this term, its studies and its notes are in Reference topic 1 of the reference library. The book gives the practical version. Get the book.