Reading focus
Syllabus: How Do Biological Rhythms Organize Sleep and Waking?
Assess the predictions of adaptive inactivity and the alternatives that could also explain variation across species.
Why you’re reading it. Introduce a functional argument that can be evaluated separately from the timing and circuit accounts.
A question to consider. What evidence would show that inactivity itself is beneficial, while leaving a restorative function of sleep possible?
Why this reading
A theory of sleep must explain variation as well as common features. Siegel asks whether the ecological value of being inactive helps explain when and how much different animals sleep. The perspective makes a substantive alternative to a single universal restorative account, inviting readers to distinguish an explanatory proposal from evidence that discriminates among proposals.
Before you read
An adaptive explanation concerns how a feature could affect survival or reproduction in an environment. It differs from an account of the neural mechanism producing that feature. Sleep rebound is increased sleep or sleep intensity after deprivation. Unihemispheric sleep involves different sleep-related activity across the brain's two sides. A physiological process occurring during sleep does not by itself show that it can occur only during sleep or explain every species' sleep duration.
Read for
- Identify what the adaptive-inactivity account predicts about opportunities, danger, energy use, and waking time. Which observations are comparisons, and which are plausible interpretations?
- Compare definitions and measurements of sleep across species. Could a behavioral measure miss local or brief sleep-related activity?
- Examine alternative functions and the possible effects of deprivation procedures themselves. Ask whether ecological and restorative explanations must be mutually exclusive.
Consider afterwards
- What comparison could distinguish an ecological explanation of short sleep from a claim that an animal needs less of a particular restorative process?
- Why would impaired performance after deprivation fail to identify one universal evolutionary function of sleep?
Editorial context
This perspective argues for an ecological interpretation; it is not a consensus that sleep has no restorative or information-processing functions. Some examples and proposed mechanisms were uncertain in 2009 and should remain hypotheses. Later recordings of frigatebirds in flight demonstrate both flexible sleep amounts and the importance of physiological measurement in natural settings. Controlled deprivation research, including Lo et al. (2016), establishes functional consequences under particular conditions without identifying a single purpose shared by every species. Ecological benefits and physiological functions can coexist.