Early protolanguage.

<p>Here the probability <i>l</i> that a linguistic principle changes increases gradually across generations by a small amount <i>δl</i>. At generation <i>1000,</i> the population, <i>M</i>, splits. The number of neutral alleles continues to grow in both subpopulations, <i>A</i> and <i>B</i>, which therefore become increasingly genetically similar (their genetic divergence decreases). Yet their languages diverge rapidly. Parameters: <i>δl = 0.1/W</i>, with <i>W = 2000</i>, <i>l(t = 0) = 0</i>, <i>l(t = 2000) = 0.1</i>; others are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0048029#pone-0048029-g001" target="_blank">Figure 1</a>.