Just about every culture in the world has this one thing in common: Children don't call their parents by their first names. Instead, they use a word such as mom or dad. The practice is shockingly consistent—as is the use of the m sound for our maternal figures (there's more variation around the word dad). As Simon Whistler explains in the video below for Today I Found Out, linguists theorize that the sounds arose from infants' baby talk, which parents then applied to themselves—ma, ba, and pa are among the first sounds that children around the world learn how to make, regardless of the language they go on to speak. For the full details, including the reason ma got applied to women, watch the video below.