Language is an interesting thing. How it changes, how we use it, the regional differences, and of course, the differences between English spoken in the US versus English spoken in the UK. I admit to being a total geek when it comes to linguistics/usage.
Recently, I had a chance to think about yes, yep, and yeah because of a self-realization. I almost never use the word yes. In fact, I'm the most likely to use it as an expression of excitement, like when my baseball team scores the winning run in a game, I'll holler yessssss! But in conversation? It's almost always yeah.
I know that yeah is considered lazy and colloquial, something that shouldn't be used professionally or in formal circumstances, but it's really difficult to change.
Some research shows that changing yes to yeah or yep is natural for English speakers because it takes less breath to say yeah and yep is even easier. This is per an answer on Quora about why three different ways to say the same thing emerged.
The title I used for this post makes me think of the Beatles, but my language pattern was in place long before I ever heard of them. Heck, it was in place long before I ever heard any rock music. As I blogged at the beginning of November, my parents didn't listen to music very often. Their radio station of choice had news, weather, recipes, etc.
It makes me wonder if yeah is a Minnesota/Minneapolis thing. Minnesota had a lot of settlement from Norway, Sweden, and Germany and the word for yes in all three languages is ja.
This answer makes the most sense to me, so I'm going with it unless something better comes along.