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Published in:
2022 | OriginalPaper | Chapter
8. Out of Africa
Author : Peter McCullagh
Published in: Ten Projects in Applied Statistics
Publisher: Springer International Publishing
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Abstract
This project was prompted by the publication in 2011 of a paper by Q.D. Atkinson, on the geographic patterns of linguistic diversity in Africa and elsewhere.
Like the genetic thesis for human migration and evolution, Atkinson’s ‘Out-of-Africa’ thesis for linguistic diversity holds that language evolved somewhere in Africa, and diffused from there to Asia, Europe and elsewhere as populations split and migrated. Since the genetic and linguistic diversity of a population is intrinsically related to its size, a small migrating subset carries less diversity than the population from which it originated. Accordingly, a subpopulation that splits and migrates carries less diversity than the descendants of the ancestral population that remains. Although tones and sounds are continuously gained and lost in all languages, the loss is supposedly higher for small migrating founder populations than for the ancestral population. In this way, the diversity of sounds becomes progressively reduced as the distance from the origin increases.
Is Atkinson’s thesis supported by the data? Before embarking on technical details of linguistic families and spatial correlation functions, a plot of diversity against distance, done separately for each major continent, gives cause for alarm. In essentially every continent other than Africa, the trend with distance is positive, not negative. This is an example of Simpson’s paradox for continuous data.
To address statistical aspects of the question, it is necessary to take account not only of distance from the origin, but also of correlations associated with geographic distance and correlations associated with linguistic family. Atkinson concluded that language evolved from a point somewhere near the coast of equatorial Africa. And that conclusion can be reproduced if correlations are ignored. But when correlations are taken into account, the analogous procedure concludes with a confidence region that includes all of Africa.
As a follow-up project for her Masters thesis, Josephine Santoso compiled a more extensive data set of 1277 world languages. This is discussed in Sect. 8.7. Where Atkinson’s phoneme response emphasized tones over vowels and consonants, Santoso’s primary analysis counts the total for all three. When all three are counted equally, the conclusion using the same techniques is that language evolved from somewhere in Europe or Africa with no strong preference from one spot over another. But the west of Ireland has the highest likelihood! All-in-all, one would have to conclude that the data do not provide strong support for the Out-of-Africa thesis.