The graph plotting lines of code vs. time is interesting. The lines for C and R steadily, almost linearly, grow over time. But the line for Fortran comprises

The graph plotting lines of code vs. time is interesting. The lines for C and R steadily, almost linearly, grow over time. But the line for Fortran comprises long level periods punctuated by sudden jumps. I assume that these sudden jumps represent existing Fortran libraries getting attached to the R system, and that organic growth of R is nearly all in R and C.