From the Jetsons to James Bond, flying via jet pack has become an icon of the futuristic way to travel. But jet propulsion is actually older than the Flintstones. It's a standard means of locomotion for jellyfish, the earliest animals to swim the seas using muscles. Jellies have been jet-propelling for at least 550 million years, yet only recently have scientists begun to understand how the challenges of moving in fluid have shaped jellyfish evolution.
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