Apparently left-handers have been in the minority for a long time, at least as far back as the Neanderthals. Researchers found the right hand was used more often than the left hand among this group when they looked at how their teeth were worn. Neanderthals softened hides by chewing and the shape of their teeth determined whether they picked the hides up with their right or left hand.
Why should we prefer one hand over the other? One theory is that handedness evolution had to do with cooperation vs. competition. Cooperation among people was important for progressing society. If the same hand was used from person to person for tools and other objects, things would work more efficiently. Preferred handedness evolved for this reason. (Why the right hand? That's not explained.) Some people remained left-handed because competition was still important for fighting and protection.
To test the competitive part of the above theory, researchers analyzed data of professional players in several competitive sports. They found there were more left-handed people playing these professional sports than in the general population, meaning greater than 10% of the athletes were left-handed with baseball and pro boxers having about 50% left-handers. This correlates with the idea that left-handers evolved to be competitive and fight to protect the tribe.
That theory was interesting, but there's got to be more to developing a preferred hand than cooperation and competition in our early ancestors, because both apes (except orangutans) and dogs prefer their right hand/paw.
To really understand handedness, we need to understand our brains and how to sort out the nature vs. nurture question. Scientists are working on it and have identified some genes associated with left-handedness. They are studying how these genes affect brain development among other things. However, that's only a small part of a very complicated question.
What I do know for now, is that my left hand works better than my right hand. And I guess that's all I really need to know.
Are you left-handed or right-handed? Do you ever think about why?
https://www.livescience.com/17009-left-handedness-ambidexterity.html
https://www.everydayhealth.com/emotional-health/0504/why-are-lefties-so-rare-blame-society.aspx
http://www.anythingleft-handed.co.uk/fighters.html
https://www.sciencefriday.com/articles/do-other-animals-show-handedness/
