"Dark Matter" in the common vernacular?

Saw in an interesting article in Time magazine about how much of who we are is determined by our siblings. What struck me though, was that in the introduction, when they were talking about scientists looking at the influence of both genes and parents, there was some missing effect akin to "dark matter":

The fact is once investigators had strip-mined all the data from those theories, they still came away with as many questions as answers. Somewhere, there was a sort of temperamental dark matter exerting an invisible gravitational pull of its own. More and more, scientists are concluding that this unexplained force is our siblings.

I think that it's great that such things can now be used for nonspecialists. There's also an article on some recently unsealed letters of Einstein which I'll have to read.