Human beings almost always have a dominant side, a preference for using one hand over the other, which we call handedness. No other animal, even apes, prefers a consistent hand as much us humans do, and it turns out that started way back in our lineage. This video from PBS Eons shows how scientists figured that out, and offers some theories of why it happened. The video is only 8:30, the rest is an ad. -via Damn Interesting
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