What began as a part of a college course on human evolution in which a few friends and I put together a set of lyrics about the evolution of sex (based on Jared Diamond's Why is Sex Fun?), kept on going as a side hobby. I suppose you might say that there has been an explosion of science rapping with a Large Hadron Collider Rap, The Rap Guide to Evolution, Tom McFadden's many raps, the Epic Rap Battles of History, the GZA of the Wu-Tang Clan using raps pedagocially, and probably many more.
I think most of the people making these raps have a certain sense of aesthetic beauty of their subject matter and are trying in their own way to put this sense of beauty/wonder into words. I suppose many of us like rap as a medium for a few reasons including its lyric-dense quality which is neccessary if you want to get a point across in a more than superficial way. But... having performed a number of these to a live audience, there is a definite limit on how many words you can use before you completely totally lose your audience's interest. So in that sense, I like the efforts like Symphony of Science, and the Imagine Science Film Festival, that incorporate some of the best emotive qualities of film/music while tackling scientific themes.
I am including these raps here with a few thoughts about how I hoped, with a specific story, to illuminate a larger aspect of the world. For example, PCR is a routine laboratory techinque but it is also a breakthrough idea that requires an understanding of the base-pairing of opposite strands of DNA, and the power of a DNA copying enzyme (Polymerase). This melting/copying of DNA is harnessed for use in the lab but it depends on the most ancient and conserved aspect of life: a template molecule that can act as the basis of heredity. So in my own way each of these raps is trying to expose something deeper and more stunning; hopefully, with a bit of humor as well.