Are the Olsen twins identical or fraternal?
June 30, 2004 12:03 AM   Subscribe

A friend of mine unyieldingly claims that Mary Kate and Ashley are in fact not identical but fraternal twins. I googled and found a lot of 13 year old girls with websites agree. A Wikipedia article says they are fraternal, an Encarta column is inconclusive. Any ideas?
posted by yevge to Grab Bag (21 answers total)
Actually, Google finds numerous articles from places like the Washington Post, the New York Daily News and E! Online that say they're fraternal.
posted by nicwolff at 12:26 AM on June 30, 2004

Response by poster: Maybe I'm blind... where are the references in Washington Post and Daily News?

It seems like every news source is repeating the same tidbit. Can anyone with any knowledge in biology explain the odds of being so identical-looking yet fraternal?
posted by yevge at 12:50 AM on June 30, 2004

knowing nothing about this situation, and whether they are fraternal, or not; fraternal, or dizygotic twins share the same about of dna as normal siblings, so the chances would be the same that 2 sisters would look that similar. (of the same age)

I haven't actually watched the shows, so is it possible they just do makeup and things to accentuate the similarities?
posted by rhyax at 1:40 AM on June 30, 2004

Well, how many ways can you say: "they are fraternal, not identical twins"?

Are you alleging some massive Olsen twin conspiracy? Maybe they're trying to convince the world that they're not identical twins because CancerMan™ knows that the world isn't ready for positive proof of the existence of a human alien hybrid intelligence that shares two bodies and is destined to the tween girls demographic with an iron fist for all of eternity? Tell me you're not serious Mulder!!
posted by Irontom at 1:41 AM on June 30, 2004

They're legal now, right?
posted by armoured-ant at 3:26 AM on June 30, 2004

They look different enough in the right ways. Heck, you could easily tell them apart back in the Full House days.
posted by skynxnex at 5:00 AM on June 30, 2004

Dude, go to the source. Page 15 of Mary-Kate & Ashley: Our Story--Updated edition : The Official Biography, "by" Mary-Kate & Ashley Olsen says "Even though the girls look so much alike, they are not identical twins. Mary-Kate and Ashley are fraternal twins. Fraternal twins sometimes look like each other, but they are not exactly the same."
posted by profwhat at 5:12 AM on June 30, 2004

It's perfectly possible for fraternal twins to look that much alike; I've been confused with my fraternal twin on numerous occasions.
posted by Jeanne at 6:22 AM on June 30, 2004

Not fraternal, sororial?
posted by crazy finger at 6:26 AM on June 30, 2004

How do you actually tell whether twins are identical or just fraternal?
posted by biffa at 6:29 AM on June 30, 2004

How about asking them?
posted by agregoli at 6:44 AM on June 30, 2004

There are two ways to know--if the twins develop in the same amniotic sac, then they are almost positively identical. The only way to be certain is by DNA testing.
posted by vraxoin at 6:58 AM on June 30, 2004

Until my (fraternal) twin brother and I were middle school aged, people confused us frequently. Nobody would ever have any trouble now (for example, I'm 6'4", he's 5'8"), but if we were to get similar haircuts and dress similarly, then...well, then that would be pretty pathetic, wouldn't it?
posted by waldo at 7:25 AM on June 30, 2004

Well, I know how to tell, but you'll have to wait until I distribute the video over the internet.
posted by XQUZYPHYR at 7:55 AM on June 30, 2004

waldo, that's quite amazing - 8 inches difference in height between you and your twin brother? That seems really extreme - is it common? Any idea what accounts for it?
posted by widdershins at 9:18 AM on June 30, 2004

widdershins, they're fraternal - no more surprising than a similar difference between siblings.

I'm surprised they're not identical twins, though. Haven't some of their movies been the kind of "trading places" things that depend on identity switching options traditionally available only to genetically identical sisters? Weird.

How do you actually tell whether twins are identical or just fraternal?

There's no little trick! Identical twins have identical DNA and come from the same fertilized egg, that then splits into two early in the pregnancy. So the two share one amniotic sac, and were actually the same being for at least a few weeks there. Fraternal twins are when two different eggs get fertilized at the same time, and both survive. So it's just like having two pregnancies at the same time, but otherwise the similarities are generally no more striking than similarities between any siblings, except of course that they're the same age at the same time (so if one kid looks just like the older bro looked at his age, etc - then as fraternal twins they'd look the same at the same time)
posted by mdn at 10:26 AM on June 30, 2004

How do you actually tell whether twins are identical or just fraternal?

Actually, it's not so easy. With genetic testing, it's become easier in the past few years. But when my twin and I were born, in 1978, the doctors just said that my parents would have to wait and see if we ended up looking different. It wasn't clear for a few months if we were identical or not -- our parents could tell us apart, but our grandparents could not. Ultimately, it became obvious. :)
posted by waldo at 10:45 AM on June 30, 2004

I remember hearing about a rare case of "half" identical twins. Rather than having one zygote split into two identical zygotes, this was a situation where one unfertilized egg split into two identical eggs, which were subsequently fertilized by two separate sperm cells. In other words, the kids' mother's genetic material was identical, but their fathers' contributions differed. The kids looked a lot alike, but were not technically identical. Does anyone else have confirmation on this?
posted by Asparagirl at 11:21 AM on June 30, 2004

Thanks vraxoin, mdn, waldo.
posted by biffa at 3:01 PM on June 30, 2004

One of the Olson twins is taller. When they were around twelve years old, the difference was particularly noticable. Since identical twins share the same genes, if Mary Kate and Ashley were identical, they should be the same height.
posted by bonheur at 3:59 PM on June 30, 2004

Fraternal twins often look more alike than children who are just siblings. In addition to the 50% (according to probability) overlap in genes that all siblings have, they also benefit from the same maternal environment while in utero. Although this won't result in, say, the development of the same eye color, it does ensure that any subtle things caused by little quirks in the maternal environment will be shared by both twins.

Also, people often get two people confused based on things other than actual static physical resemblance. Things like similar gestures and facial expressions can really amplify even a minor resemblance. For example, I am confused with my best friend all the time, despite the fact that we really don't look similar at all. Fraternal twins are very likely to share a lot of intangible things like that, since they often spend more time together than you would expect from siblings with a separation in age. Since they're constantly providing each other with non-verbal feedback, they tend to converge in a lot of their unconscious habits.
posted by LittleMissCranky at 7:28 AM on July 1, 2004

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