Ancient viruses helped speedy nerves evolve
The trick happened multiple independent times in jawed animals
![Stacks of long tubes of various lengths are seen. Inside the tubes is a bright purple "filling". This is the long part of a nerve fiber called an axon. Around those fibers are thick tubes colored brownish-gray that form an insulating sheath around the nerve. Some wispy strands of connective tissue lays over some of the tubes. Connective tissue is colored hot pink.](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2024/02/021424_ts_ancient-viruses-nerves_feat.jpg?fit=1030%2C580&ssl=1)
An ancient virus may help myelin (grayish brown) form a sheath around nerve fibers (purple), as shown in this colored scanning electron micrograph of a broken bundle of nerves. Connective tissue (pink) encases the nerve fibers.
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