The only Marcus I know personally is a Canadian of Chinese descent. Just sayin’.
As she should. “Gag” is ever so much more melliphonious. 
I don’t use my “unique” first name. I hate it. I hate spelling it, I hate correcting people’s pronunciation of it. I’ve had to correct misspellings of it all my life. There’s a REASON why I go by Lynn.
My (white as snow) mother was extremely pregnant when she dreamed up my name, it’s an alternate spelling of a common Italian girl’s name. Now that she has Alzheimer’s, and won’t know the difference, I’m thinking of getting my name legally changed. When I brought up getting the name change some years ago, she was very upset about it. Apparently she thought that it’s a beautiful name. Maybe it is, but the hassle that goes with it is ugly.
I on the other hand enjoy telling people my real name, and love the telemarketer shibboleth.
Though I still don’t get how some people who have only heard my name still say it as if they’d read it.
I thought it was that white slave owners would name their slaves after Romans and then this tradition persisted after slavery was over.
Considering the etymology of Marcus, the Oxford Classical dictionary guesses: “Marcus might (…) refer to the month of birth (thus a Marcus would have been born in March, the month consecrated to Mars.” That is under: names, personal, Roman. So that theory has at least some respectable support. Oh and to nit pick the archaic variant of Mars is Mavors instead of Mamors.
Although I’ve seen the name more common among black people, I and my wife are both white, and our son’s name is Marcus.
Marcus is an extremely common name in Europe. According the the SSA website, in America Marcus took a sudden large jump in popularity in 1970, maintained at around the same level of popularity until it began to slide back down in 1996, and remained in the top 100 names for American boys until 2000. So it is a fairly common name for men and boys born in the 70s, 80s, and 90s, and I highly doubt most Marcuses are found within less than 6% of the US population (black men/boys). I think the OP’s observation is confirmation bias/coincidence.
Trends in names are unpredictable. I’ve known several white Marcuses, but all but one went by by Marc. Don’t remember if I’ve ever met a black Marcus. I went to high school with a black guy named DeMarcus, which sounds/reads to me as a typical black American name. There are two relatively well-known (I say this because I know them…) black American athletes named DaMarcus (Beasley) and DeMarcus (Ware).
That’s an interesting observation. I never thought of it before but now that you brought it up there seems to something to it. Not absolute, but still with enough anecdotal evidence to take notice. In a sense, the longer version of the name seems to bring more class and dignity. Maybe that’s the underlying reason. I have no problem with it and actually like it.
We’ll give Lew Alcindor a pass. But if I was given the name Ferdinand Lewis I would probably change my name to Kareem. http://en.wikipedia.org/wiki/Kareem_Abdul-Jabbar 
Well, in the real world, my friends call me Hawk.
I could lie and say it was because Gagundathar is too difficult to pronounce, but it was really because my given name was so dang common.
Think. If you walk into a room and someone says, “Hey, John” and you assume it means you and IT DOESN’T, it kind of puts you off of your game.
BTW, John is not my given name, but the example is valid.
So, going by ‘Hawk’ is much much better.
At least it is in friendly territory.
Lynn, did you choose that name as an online persona, or do your friends in the ‘real world’ call you that as well?
I only ask because the idea of tagging a human with a crappy name is a significant issue with some of my friends. Naming your male child ‘Marcus’ is pretty cool. The first Marcus I think of is ‘Marcus Aurelius Antoninus Augustus’. Co-emperor with Lucius Verus.
However, if you give your child a name like ‘Shanaquiquia’, then you have left that little girl in a difficult position. On the other hand, if you give her a name like ‘Shaniqua’ then you have blessed her with not only a pretty name but also the opportunity to celebrate the Latinism of the QU diphthong used in common interrogatives.
Curiously, in some old cultures like that of parts of India, the shorter the surname, the older the family. Apparently, as time goes on the names get longer, so that a man with a surname of ‘Patil’ is of an older (an usually more influential family) than one named ‘Thiruvananthapuram’. Or so says my friend from northern India whose last name is ‘Dave’.
I think black conventions for shortening names differs from whites. Jim as a derivative of James is much like Dick is to Richard or Bill is to William. Which is to say, these nicknames are artifacts of culture more than anything else. An alien from outspace wouldn’t automatically assume the shortened version of James was Jim, so we shouldn’t perceive this convention is the default.
Black men go by shortened names all the time. “Deangelos” go by the name “Dee”, “Terrells” go by “Tee”, and “Michaels” go by “Mike”. My (black) brother Jacob goes by Jake. I could see a black Marcus calling himself Marc just as easily as I can see him calling himself Marcus.
Please, it is “Captain Mike Hawk”, danggit.
Taking a guess that it is from the book of the bible, Mark, formalized as Marcus because it sounds better.
I would think it had a lot more influence in the black community (and all others) in America than the Roman god of war.
Lynn is my meatspace middle name. My family and one friend call me by my first name. Everyone else, including my husband, calls me Lynn, because I won’t answer to anything else. When the med assistant calls me into the treatment room, and does so with my first name, I’ll reply “I go by Lynn, that’s why I circled it on the form”, for instance.
Bodoni is my maiden name. If I’d had a WASP last name, I think that I would have been OK with an oddly spelled first name, but as it was, too many people couldn’t pronounce either name. I dunno. I think that it’s one thing if a person decides in his/her teens or twenties to choose a non-standard name…but to be saddled with it from birth was not pleasant, for me.
Older members may recall the caucasian Marcus Welby, M.D. from TV in the early 1970s. The younger crowd may remember him from that song Smashmouth released in 1997 about him walking on the sun.