Are there dark origins behind "Step On A Crack and Break Your Mother's Back?"

(the following is a cross-post from one of our blogs, Playground Jungle):

Here’s one that everyone knew to chant while walking down the sidewalk:

Step on a crack, you’ll break your mother’s back.

This has been recorded in print since at least the late 19th century, often with a few additions:

Step on a line, break your mother’s spine
Step on a hole, break your mother’s sugar bowl
Step on a nail, you’ll put your dad in jail

So the thing to step on here is probably a bowl. Everything else will kill people or, at least, uproot your life considerably. One can survive the loss of a sugar bowl. Health nuts will even say that you’ll benefit from it.
One person I knew added another:

Giggle while you pee, you’ll turn into an old dead tree.

Stepping on cracks has long been subject to superstition. In addition to the danger of breaking your mother’s back, a 1905 book, Superstition and Education, lists several other grim superstitions: that if you step on a crack, you will have bad luck, or that you will not get a surprise at home that you otherwise would have.
Many claim that the original rhyme was “step on a crack and your mother will turn black,” and that the superstition went that stepping on a crack meant that you’d have a black baby. Indeed, Iona Opie noted that that one was fairly common in parts of the UK in the 1950s, but there’s no real reason to think it’s the original, not just another variation that came and went - the idea that it was the original probably comes from people who pick that one line out of Opie's long entry on the subject. 
At the same time, kids were saying that if you stepped on a crack, you’d be chased by bears. This idea was invented by A.A. Milne in his poem “Lines and Squares,” but, from Opie’s description, was a more widespread superstition than the racial one.  You have to watch out when people tell you the "original meanings" of things -  like the supposed "secret origins" or nursery rhymes that go around, they're seldom true. And this is coming from the blog that connects songs about pooping in your overalls back to ancient ballads about making violins out of dead bodies.
These are all, in any case, some of those superstitions that no one really believes. While the good luck brought from a penny can be debatable, most kids figure out right away that people who step on cracks in the sidewalk don’t come home to dead mothers and don’t get chased by bears (at least not very often).

The Smart Aleck's Guide to Naughty Playground Rhymes and Children's Folklore ebook will be out next week!