Where Sleep Came From: teacher key

How Animals Sleep, grade 12 edition, written for 12th grade and up. Jellyfish, lizards, birds and seals all seem to sleep, yet no one can say exactly why. Follow the evidence for what sleep is, what it costs and where it began.

Read the book. Print this page for the key.

Questions and answers

1. What three signs do scientists use to call a rest sleep?
   • The animal is quiet, reacts less, and sleeps more after being kept awake (answer)
   • The animal is warm, hungry and fast
   • The animal is blind and in a den
2. What did the 2008 review find about REM sleep?
   • Convincing evidence in reptiles, fish and insects was lacking (answer)
   • Every animal has REM sleep
   • Only birds have REM sleep
3. Why might lizard sleep matter for the history of sleep?
   • It is simpler, so it may be closer to the ancestral mode of brain sleep (answer)
   • Lizards sleep the longest
   • Lizards were the first animals
4. What does the frigatebird study suggest about half-brain sleep in flight?
   • Birds sleep 20 hours in flight
   • Staying alert usually demands more attention than half-brain sleep allows (answer)
   • Birds never sleep
5. What is the best summary of what scientists say about why animals sleep?
   • Sleep is widespread, but its functions remain enigmatic (answer)
   • The question is settled
   • Only humans need it
6. What does enigmatic mean here?
   • Hard to explain (answer)
   • Very loud
   • Easy to see

Words

• unihemispheric: one half-brain
• torpor: deep rest
• adenosine: a body chemical
• enigmatic: hard to explain
• ancestral: from long ago