Evolution depends, in part, on random flukes: some gene somewhere gets changed somehow. If the change is for the better—if it allows the organism to live and reproduce more successfully—eventually it becomes more and more common.
In humans, right-handedness is caused by genes—genes that also, as it happens, affect a whole range of brain behaviors. The genes that cause right-handedness cause the human brain to specialize, to become more proficient and efficient at certain tasks.
But left-handedness, says Joe Hanson in the video above, carries no similar benefit. There is no gene for left-handedness, says Hanson: instead, left-handedness stems from not being right-handed. But if being right-handed confers all sorts of proposed evolutionary benefits, such as processing language more readily, then why are some people left-handed?
As a partial answer, says Hanson, it may come down to the underdog approach to evolution: being a wildcard.