Rejection of a serial founder effects model of genetic and linguistic coevolution

Abstract

Recent genetic studies attribute the negative correlation between population genetic diversity and distance from Africa to a serial founder effects (SFE) evolutionary process. A recent linguistic study concluded that a similar decay in phoneme inventories in human languages was also the product of the SFE process. However, the SFE process makes additional predictions for patterns of neutral genetic diversity, both within and between groups, that have not yet been tested on phonemic data. In this study, we describe these predictions and test them on linguistic and genetic samples. The linguistic sample consists of 725 widespread languages, which together contain 908 distinct phonemes. The genetic sample consists of 614 autosomal microsatellite loci in 100 widespread populations. All aspects of the genetic pattern are consistent with the predictions of SFE. In contrast, most of the predictions of SFE are violated for the phonemic data. We show that phoneme inventories provide information about recent contacts between languages. However, because phonemes change rapidly, they cannot provide information about more ancient evolutionary processes.

Figure 1.

African versus non-African (a) alleles and (b) phonemes.

Figure 2.

Total and private alleles and phonemes. (a) Total alleles; (b) total phonemes; (c) private alleles; (d) private phonemes. The single Australian sample is omitted from the genetic analysis. Af, Africa; Eur, Eurasia; EA, East Asia; Oc, Oceania; Am, Americas.

Figure 3.

Within-group diversity versus geographical distance from origin. (a) Microsatellite heterozygosity versus geographical distance, best-fit origin. (b) Correlation coefficients for microsatellite heterozygosity versus geographical distance when using each population location as the origin. (c) Number of phonemes versus geographical distance, best-fit origin. (d) Correlation coefficients for number of phonemes versus geographical distance when using each language location as the origin. Geographical distances are through waypoints on land.

Figure 4.

(a) Rooted NJ tree for the genetic data. (b) Between-population heterozygosity versus geographical distance. (c) Midpoint-rooted 50% majority-rule tree for the phonemic data. (d) Between-language phonemic difference versus geographical distance.

Figure 5.

Phonemic difference versus geographical distance. (a) Afro-Asiatic language family. (b) Africa. Figures S2 and S3 in the electronic supplementary material show the plots for other language families and geographical regions.