I'm not sure which animal dreams the most, but I've heard that echidnas and marsupials in general have a lot of REM sleep. Recent work shows that even reptiles dream. Without that, animals could just be quietly vigilant.Ī: The natural history of dreaming is a fascinating question. This is a fundamental criterion for measuring sleep in animals, called 'increased arousal thresholds'. But they weren't dead - they just needed sleep. I can tell you that after a couple days of sleep deprivation, these flies were not budging. When my friend Paul Shaw first started looking for sleep in flies, we would spend all-nighters trying to keep them awake, tapping on the tubes they were housed in. Q: Is it relatively as easy to wake most animals from sleep as humans?Ī: It is almost impossible to wake up a severely sleep-deprived fly. This is just a hypothesis, but worth debating I think. This co-evolved with a need to sleep, to curate those attention mechanisms. Carrying this further, I think consciousness emerged from animals that have attention. By the same token, I don't think worms have a selective attention. I think that some aspects of their development have similarities with some (deep) sleep functions, but I don't think they have a 'sleep switch', meaning the capacity to rapidly and reversibly turn off responsiveness to the outside environment. I don't think worms sleep in the same way flies and humans do. elegans), which is where the sleep research was done. Why do worms need to sleep? Do flies sleep like worms?Ī: By worms, you probably mean nematodes ( C. So it isn't so much a linear increase in complexity as a step function. After that, sleep was also a need to acutely ignore the world for a while so as to be able to pay attention to it properly while awake. Before that, sleep 'functions' were just molecular processes linked to developmental transitions, often associated with quiescence.
Q: Would you say that as developmental complexity of an organism increases, the need for sleep increases? Does the importance of sleep decrease in lower order organisms such as invertebrates with shorter life cycles? I would think that their biology would be skewed towards more 'core' functions such as reproduction?Ī: I think that the key 'complex' point in evolution associated with sleep need, is the brain can selectively pay attention to the world. Personally, I don't think fly larvae show spontaneous sleep patterns I think that, like nematodes, their sleep-like functions are all linked to programmed developmental changes. These relate more to development, and deep sleep is like a mini-development in a way, with physical changes happening at synapses. Q: Do Drosophila (fruit fly species) show similar spontaneous sleep patterns to humans?Ī: It isn't known whether larval flies sleep, although key sleep-like functions probably happen during metamorphosis, as has been shown in the nematode C. This has not been a good evolutionary strategy in general. Some animals get all their mating done without sleeping much. I think there may be a male bullfrog out there that doesn't sleep, but it's probably in a pretty ragged condition. If they don't sleep, there will be a price to pay at some point. All animals with a brain sleep, as far as this has been carefully examined. It all relates to the multiple functions of sleep, and how these can be accommodated into an animal's specific niche.Ī: Yes.
Clearly this has nothing to do with intelligence or brain size. At the other end, some bats sleep about 18 hours. Even worse, ungulates (cows and antelopes and such) only sleep for a couple (maybe 3-4) hours. Q: Why do some animals sleep for much longer than others? For example, a lion sleeps for around 20 hours a day but a cheetah sleeps for 12 hours.Ī: This is a big mystery.
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