A study recently published in a prestigious journal reports a surprise finding: that jumping spiders twitch during sleep in a way that resembles what cats, dogs and other mammals do during rapid eye movement (REM) sleep. The German researchers noticed eye movements happening at the same time as leg jerks, suggesting that these spiders dream. Similar evidence has been recorded for two other invertebrates — octopuses and cuttlefish — as well as birds and fish.
Do these animals dream the way we humans do? While they obviously can’t tell us, the evidence is increasingly persuasive, especially if we bear in mind Darwin’s dictum that differences between species are a matter of degree, not kind.
As argued by David Peña-Guzmán in his recent book, “When Animals Dream,” dreaming indicates that an animal is sentient — a unique individual who experiences life and processes it via thoughts and feelings. Putting it another way: Animals have biographies, not merely biologics.
The implications, we believe, are compelling.