Some friends here in Uruguay met some other Cohens, and they were asking if we were related. So then my family (mostly my dad and sister) had to collaboratively explain several Difficult Topics in our very much in progress Spanish.
Like a real "How do you say 'pogrom'? 'El pogrom'? Really? Ok, have you heard of Ellis Island?" conversation.

(The backstory here is that a lot of similar Jewish names got turned into "Cohen" at Ellis Island, where a lot of Jews were coming into the US because of all the pogroms.)

Edit: I'm being told that the Ellis Island changing names thing isn't true? The more you know.

@BathysphereHat There is little to no evidence that names got changed at Ellis Island and TONs of evidence that we changed them later. Dara Horn, among many other scholars, have repeatedly debunked this.
@sng Oh huh, good to know! Do you have any resources about that? I would love to know more.
@BathysphereHat The relevant chapter in People Love Dead Jews has a ton of citations. That’s the one I know off the top of me head.
@sng Ok, I'll check that out when I get around to reading that (it's on my list, but you know how it is). In the mean time, I found this. https://www.nypl.org/blog/2013/07/02/name-changes-ellis-island
Jewish Americans changed their names, but not at Ellis Island

Today, members of many white ethnic groups – including Jews, Italians and Poles – believe that insensitive or ignorant Ellis Island officials changed their families’ names when they arrived in the U.S. to make them sound more American.

Michigan State University
@sng Awesome, thanks!
@BathysphereHat Last names in Europe trace back to the 1787 decree by the Hapsburgs that we had to pick last names and then spread from there during the the Modernity Crises. Source my rabbi who was a history major. That should be enough search terms to find something.
@sng It's so interesting that last names are that recent.
@BathysphereHat Yeah. Learning that really broke my head.

@BathysphereHat @sng

Some last names are much older. The REQUIREMENT to have a last name was new

@BathysphereHat @regordane Thank you for the additional context. My knowledge of this is based off of one 20 minute conversation so, yes, I’m missing a lot of nuance and detail. Appreciate it!

@sng @BathysphereHat

Yes. But Cohen is special. It indicates patrilineal priestly descent. It's not a surname that someone who wasn't a Cohan would have chosen (the rabbis would have made sure of that).

There is scientific evidence to support this, although it points to multiple clans rather than a single founder (by tradition, Aaron).

https://en.wikipedia.org/wiki/Y-chromosomal_Aaron

Y-chromosomal Aaron - Wikipedia

@BathysphereHat Sorry about the flood of responses. Interesting detail. My shul, in Texas, has a lot of members who have discovered that their family ended up in the Americas when Spain kicked the Jews out.
@sng No problem, you've given me a lot of great info! And yeah, that is interesting.