It’s absurd because the term “Arab” is very seldom used in any sort of linguistic context and the linguistic context is certainly not “by far the most common” context.
The Arab oil embargo could not have been the Tagalog oil embargo.
The Arab spring could not be the Esperanto spring.
The Arab-Israeli conflict could not have been the Hindi-Israeli conflict.
It’s not about language.
DNA studies are statistical in nature, and wouldn’t necessarily tell you about specific individuals. One cannot tell from DNA if a person is a Levite. There is a certain Haplogroup that is more prevalent among Levites, but it’s not a definitive test-- I think it’s about 50% accurate, and only among Ashkenazi Jews.
Let’s not overgeneralize. Many people in the West use the terms interchangeably, but not all. And certainly not in any official capacity. And I don’t know how common this is outside the US, but let’s remember that “the West” is a lot bigger than the US.
It most commonly is about language.
I guess the only person you can safely say is an Arab now is Ahab.
Except he wasn’t an Arab, he was an AY-rab. 
Prove it.
Persians and those from the Arabian Peninsula.
What are you talking about? Persians are Persians. Farsi is an Indo-European language.
No. We don’t say the Arabic oil embargo. We don’t say the Arabic Spring. We don’t talk about the Arabic-Israeli conflict.
We’re talking about the most common way to establish what we mean when we say such and such person is an Arab. And the most common feature uniting Arabs is the Arabic language. Not genetics, not geography and not religion. I could quite wiki to support this, but instead I’ll just quote the very first line from Albert Hourani’s A History of the Arab Peoples: The subject of this book is the history of the Arabic-speaking parts of the Islamic world….
Like I said there are exceptions like the one I quoted above or to go in the reverse direction I’m sure you can find Arabic-speaking Berbers ( with Arabic as their first language ) that identify primarily as Berbers. Ethnic identity can be slippery at times. But accepting that there are exceptions, in general the most overall useful definition is that an Arab is someone for whom Arabic is their first language.
I’m sure you’ll correct me if I’m over generalizing but using this map isn’t Persia all of Arabia? Which is generally where Arabs are from?
[QUOTE=Tamerlane;14687285Under a linguistic definition, which is by far the most common way of defining what is an Arab. If Arabic is your native language you are an Arab. [/QUOTE]
There is absolutely no reason that the word “Arab” and the word “English” or other linguistic terms should be expected to have parallel definitions. That’s not the way the English language works. “English” is not defined as someone who speaks English, but “Arab” is most commonly defined as someone who speaks Arabic as his or her native language or is descended from such people. They’re different words. They’re defined differently and that’s just the way it is.
And no, there likely aren’t DNA studies, because an Arab identity is not dependent on genetics.
Nope. Arabia is that chunk of land south of the Achaemenid Empire which is mostly not colored in because it was not part of it ;).
Beyond that the Achaemenid state was a multi-ethnic one, ruled by a Persian elite, but which had adopted a non-Persian language ( Aramaic in this case ) from the dominant conquered culture of the Babylonians to serve as the administrative lingua franca ( which would remain the case until the Sassanians, ~seven hundred years later ). Persia in the sense of the homeland of the Persian people at that time referred most accurately to the province of Persis on the gulf, also labeled on that map. This would change over millenia, but I’m afraid you can’t look at a snapshot from 500 B.C. to determine modern ethnicities.
You might be mistaken because they put the title, “Persian Empire”, right smack in the middle of the Arabian Peninsula, but they are referring to the colored in area, which is outside the AP. That was just a convenient place to put the text, and shouldn’t be interpreted to mean it designates that area on the map.
I intended to suggest that various groups of Arab speakers (to follow Tamerlane’s definition) may have common “DNA markers”, whatever those are. 
For example, people of European descent have Neanderthal DNA and people of African ancestry do not.
The linguistic and genetic groups would have some overlap, but there would be lots of mismatches. Most of North Africa is going to be different from the Levant. You might find Middle Eastern Arabs more closely related to Jews than to Algerians, for example.
Generally speaking, people who live in close proximity will have similar genetics. And the farther away you go, the less similar it becomes. This assume you are looking at people who have not been subject to mass migrations, like what you’d find in the US.
I don’t know any Arabic, but I’d assume the language also becomes more diverse with distance from the Arabian Peninsula.
It depends on what you mean by “diverse.” Generally speaking, languages are more diverse, from a linguistic point of view, where they have existed for a longer time. So, at the point of its origin, it would be the most diverse.
I suppose I meant the inclusion of other languages and local idioms, but as you say, it would be less diverse than a centrally located origin which would include many of those things from different regions. Not sure what word describes what I’m going for here.
An Arab is someone who self-identifies as being an Arab, or, not him/herself so self-identifying, belongs to a subcultural group which generally identifies as being Arab.
For members’ reference, Wikipedia 's article on Arab people. To me it seems accurate in broad terms, though I can see a lot of points at which a scholar like Tamerlane might cavil.
For the record, on the question of language as a pointer: prior to 2003 Iraq had about 170,000 Assyrians resident. This was their self-identification owing to being indigenous Nestorian Christians; the degree to which they were descended from the Ninevite-governed Assyrians who came down like the wolf on the fold is probably about on par with the typical modern Frenchman’s degree of descent from the Gauls.
A cultural identity as “Arab” in modern MENA appears to me to be about equally slippery to pin down.
