This doesn't seem as mysterious to me as the article suggests. We were still primarily roaming hunters 1.4m years ago. It's not difficult to imagine the uses a more aerodynamic rock would have...namely, you could be more accurate throwing it.

But I'm sure this occurred to researchers, so maybe they're expressing this as "there is no evidence of how they were used" and not "we don't have some good ideas."

Witness arrowheads - every plowed field in the American midwest has arrowheads. Because they were used for thousands of years, and lost for thousands of years.

Maybe you have passed such things multiple times without ever recognizing their true origins!

Have look at the pic in the article, not exactly polished ball bearings.

Those would be easy to ignore and nature makes plenty of more spherical rocks. Most rivers have shores with better looking "spheres".

I don't have the expertise to comment on if that is correct or not. I'm just repeating what 'facts' that I trust the reporter verified, though i'll admit to seeing enough examples of reporters not verifying facts to have doubt.

Combine that with the fact that we're temporally very close to the Indigenous occupation. Whereas there's over a million+ years of geological processes to affect those artifacts original provenance.

Also, if we haven't been looking for crudely rounded stones we aren't going to have much of a sample size to say whether or not they are, to use archeologist's favorite word, ubiquitous.

I'd wager most people aren't aware that spheres aren't common in nature.

We can start to unpick the mystery with insights like that.

That decrease in free time is one way some theories tie farming to alcohol production. As substance is far more difficult when farming.

Here is a study with modern people:

https://www.cam.ac.uk/research/news/farmers-have-less-leisur...

Wikipedia says: "The sling is an ancient weapon known to Neolithic peoples around the Mediterranean, but is likely to be much older. It is possible that the sling was invented during the Upper Palaeolithic at a time when new technologies such as the spear-thrower and the bow and arrow were beginning to emerge."

Seems unlikely, though - 1.4m years vs 50k years.

I mean David/Goliath wasn't totally made up for fun, slings were a key weapon in early warfare. They work.

They aren't kidding about them being used as lawn decorations for ticos, in my neighborhood there were at least three, and one in a park.

https://en.m.wikipedia.org/wiki/Stone_spheres_of_Costa_Rica