This is--hands down--my favorite article that I use with AP Biology. It's so engaging, interesting, and it's easy to understand (it is long, though). The article is about the silver fox experiments done by Dmitry K. Belyaev; it's a perfect example of artificial selection and ties into evolution units so well.
The article is 10 pages long and can be found at: http://tinyurl.com/k472gw5
I wrote the questions to use with my AP Biology class. They correspond with the article and go in order. My students will read the article and answer the questions as an assignment; we will discuss the info the next day. They ALWAYS talk about how interesting the article is--again, even though it's long, it's super interesting and your students will be really engaged!