stargazer9927 wrote:I just learned about it last year, and we saw lots of videos on it. Why would they teach you something that's untrue in school? It's also been other places. Where did you hear it was debunked?
They teach many things that are untrue, outdated, or else have not been verified in school, which is why verifying one's sources and their currency is important.
http://www.nature.com/nature/journal/v4 ... 6142a.html
That's the link to the actual paper published. There were two conclusions: vanishing twins are not as common as claimed, and that the presence of one embryo does not impact the development of its twin. The second conclusion in particular means that having a twin that vanished does not mean that you will be left-handed.
There's also the matter of how the vanishing twin theory usually deals with an identical twin vanishing. Identical twinning is not that common (~0.3%) with twinning in general only occurring ~3% of the time. Considering that left-handedness is estimated to occur in ~10% of the population, that's more than ~7% more lefties than the vanishing twin theory allows for. Combined with findings that left-handedness has been shown to be linked to specific alleles of LRRTM1 gene and that variations in testosterone also affect development, and the whole "you're left-handed because you were on the left side of the womb when your twin vanished" thing really doesn't hold any water.
And while it's true that a high proportion of twins have a lefty/right split, not all twins have opposite handedness from each other, and there are plenty of left-handed folks who did not have a vanishing twin.
