If people were only fighting and competing throughout human evolution, natural selection would lead to more lefties being the ones that made it until there were so many of them, that it was no longer a rare asset.
Se só houvesse luta e competição ao longo da evolução humana, a seleção natural levaria a mais canhotos sobrevivendo até que houvesse tantos deles, que já não seria mais uma habilidade rara.