You've probably heard that organisms evolve over time. Well, life is complicated, and sometimes things devolve instead — to devolve is to get worse instead of better.
The de- in devolve is a clue to its meaning. When things devolve, they deteriorate, degenerate, fall apart, go to the dogs, and generally end up worse. When a classroom gets loud and rowdy, a teacher might say the class has devolved. There is another, less negative, meaning of devolve. You can devolve responsibilities: for example, the U.S. government could devolve a certain responsibility to the states. The non-negative meaning of devolve is kind of like passing things on in a will. If I devolve something to you, you inherit it.