which is one of the slowest cases,by plotting their progress charts.Figure
20.1 shows modal song change for a coevolving surprise-scoring small
(i.e.,sample size two) population.The relatively small region of dark
points,indicating small changes between past and present generations,
is dominated by a large light region,indicating large changes over time.
In figure 20.2,we plot the chart for a fixed-preference global-transition-
scoring large (twenty) population.Here the differences between present
and past modal songs are mostly small (dark points),meaning that little
change occurred over time.The light band along the diagonal indicates
a lot of change in the first few generations,as initially random male songs
were most strongly winnowed down,but after that little more transpired.Resulting Song Diversity within Populations
To measure the synchronic diversity of songs within a population at any
particular generation,we computed the set of differences (again zero to
thirty-two) between every pair of males’ songs in the population.This
set of differences can be plotted as a histogram for any given generation,381 Simulating the Evolution of Musical Behavior
Figure 20.2
Change in modal song for a noncoevolving global-preference sample-size-twenty popula-
tion,showing little change over time.Fig.20.2