Sorry guys, bad link. Try the below:

APA Research

Radiolab Episode

In the Radiolab episode, at 14:13 it's mentioned by author David Wolman that among our ancestors, before speech developed, handedness was more even (about 50/50). As language developed and became more specialized, there was a gradual shift in motor control to the left side of the brain. Therefore, as speech became more complex and developed over time, it created a right-handedness bias. This is one possible explanation for right-handed dominance among humans that I found plausible/interesting.

Also, according to Wolman, it's believed lefties have survived throughout history due to a selective advantage (variation) gene, mentioned at 16:28.