Self-study
No one knows what purposes, if any, dreams serve, although there are a number of hypotheses. █████████ ██ ███ ███████████ ██████ ███ ████████ ████ ███ █████ ██ ███████ ████████████ ██████████████ █████████████ ██████████ ████████████ ███████ ███████ █████ ██████████ ██████ ███ ███ ███ █████ █████ █████████ ████ ██ ███ █████████ ██████████████ ███ ████ ██████ ████ ████ ███ ████ █████ ███ ████████ ██████ ██ █████ ██ ██████ █████████ ████ ███ ████ █████ ███████ ██ ███ █████ █████████ █████ ███ ████ ████ ██ █████████ ██ ████ ██ ███ █ ████ █████ █████ ████████ ██ ███ ██████████ █████ ████ ████ ████████ ████ ████████████ ███ ███ ████████████████████ ███████████ █████ ███ ██████████ ████████ ████ ███ ██ ██████ ████ ███ ███ █████ ██ ████ ██ █████████ ██████ ████ ██████ █████ ████ █████ ██████ █████ ███ ███ █████████ ████████████
Argument Structure
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Cleaning House
Here’s a casual summary of the argument:
Phenomenon: We dream.
Hypothesis: We dream as a side effect of unclogging our memories.
Prediction: If this is true, we would expect animals that don’t dream to need extra memory space for all their clogged-up memories.
Evidence: The spiny anteater doesn’t dream (or at least, doesn’t do REM-sleep), and has a ridiculously large brain.
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Conclusion: Maybe this hypothesis is onto something.
22.
The parasitic-connection hypothesis, if true, ████ ████████ ████████ █████ ███ ██ ███ ██████████
a
The animals with ███ ████████ ██████ █████ ███ ████ ████ █████████
We know that spending zero time dreaming is associated with bigger brains, but we don't know if that pattern extends as a clean correlation across the spectrum from smallest to largest. Other factors could contribute to those teeny-tiny animals' need for sleep (or lack thereof).
b
Immediately after a ██████ ███████ ████ ██████ ██████ ███ ██ ███ ██████ ████████ █████████ ██ ██████████ ████████████ ███████ ██████
"Virtually no" is a much-too-strong absolute claim. (B) would be supported if it said something like "her or his memory tends to contain fewer accidental associations..."
c
When a mammal ████ █████ ████████ █████ ██ █████████ ████ █████████ ███ ███████████ ██ ███ ██████ ████ ██ █████████
This is directly supported by the phrase "which would otherwise clog up our memories" from the stimulus. If dreaming is what happens when we're unclogging our memories, preventing that process would clog up our memories, impairing them.
d
Insofar as a ██████████ ███████████ ██ █ █████ ████████ ██████████ ████████████ ███████ ██████ ██ ██ ██ ██████████ ████████████
This creates a strict rule that dreams must only involve meaningless connections, but we don't have any information about how the "unclogging" process works, or whether it works perfectly. Perhaps erasing parasitic connections involves recalling a bunch of meaningful connections by comparison. Perhaps the brain often mistakenly erases meaningful connections as well, causing them to appear in dreams.
e
All animals other ████ ███ █████ ████████ ██████
The spiny anteater is the only mammal that doesn't have REM sleep. Plenty of other animals (birds, reptiles, horrific arachnids) could still dream, and it's even possible that some mammals have REM sleep but do not dream.