I briefly investigated how to draw curved arrows in R. Here’s a small piece of the figure that I ultimately created: A google search for “curved arrows in R” revealed three options: curvedarrow in the diagram package The internal function igraph.Arrows within the igraph package (mentioned by Gabor Csardi in R help) Using xspline for the shaft and adding the head “by hand” (mentioned by Greg Snow)
![Curved arrows in R](https://cdn-ak-scissors.b.st-hatena.com/image/square/604242d6e5418880ae23da0e17f89c2709bef3db/height=288;version=1;width=512/https%3A%2F%2Fkbroman.wordpress.com%2Fwp-content%2Fuploads%2F2012%2F10%2Fsample_mix-ups.png%3Fw%3D224)