For most of history, it was thought that left-handed people were afflicted, evil, or possessed. Preferring the left hand was considered unnatural. In fact, we get our word "sinister" (and the less well-known "sinistral" from the Latin "sinistr-" meaning "on the left". Likewise, the English "left" is derived from the Old Saxon word "lyft", meaning worthless.
Up until about the 19th century, children whose natural inclication was towards left-handedness were forced by strict punishment to use their right. This was practiced even in the United States. Only very recently has being left-handed begun to lose it's negative reputation. Now, being left-handed is often associated with creativity and intelligence.
Handedness is determined physically in the brain. The corpus callosum of left-handed people is noticeably thicker (some statistics say about 11%). Regions of the brain that only appear in a certain hemisphere in right-handed people such as speech, will often appear in the other hemisphere or both in sinistral.
Reliable statistics about handedness are very hard to get even today because of the stigma attached to it, but it is estimated that about 10% of the population is left-handed. It is commonly accepted that men are more often left-handed than women, but by how much is not known.
The statistic that left-handed people do not live as long is a myth. It was based on one study, which has been discarded by the scientific community since then.