[vacri]

Two things missing from the article: physical repair is improved in sleep; and the laydown of long-term memories is an important part of sleep. You can screw up someone's memory of the previous day by waking them at the right times.

And, as usual, REM sleep steals the show. Probably because of that funky acronym, and that's when we tend to have movie-like dreams. Wake people up at the right time in slow-wave sleep and they'll report 'dreams' that are just sounds or flashes of light.

Bonus factoid: you can wake most people up from even deep sleep by calling their name a few times. When I was a 'sleep technician', that's how I used to wake people up when I had to fix a sensor - much more gentle than physically touching or shaking them.

It's a bit disappointing that journalists are still peddling the "sleep is a great big mystery" angle. And also that the article is arguing that there must be one particular reason why we sleep. There isn't one reason why we respirate, one reason why we digest, or one reason why we circulate - why should there be one reason why we sleep?

[tremon]

In my mind, all of your other examples have a singular answer, even if the answer isn't the full story.

one reason why we respirate

To replenish the oxygen in our blood.

one reason why we digest

To extract energy from our food.

one reason why we circulate

To distribute nutrients around the body.

Simplified as those answers may be, they're not wrong FAFAIK, they're incomplete. Do we have such a single not-completely-wrong answer for why we sleep?

[vacri]

Well, the one thing you've missed in all the items is waste removal, which is just as important as nutrient distribution. Also, we absorb more from our food than just energy. And even then, you caveat your answers with "but these are simplified and incomplete".

Then compare to the article, a bit of long-form journalism rather than throw-away summary lines, which opens with the statement that there's one crucial reason for sleep and we don't know it.