Language serial founder effects?

I'm at the American Association of Physical Anthropologists meetings this week, so I haven't had time to keep up with the press. Tonight I see this story about a new paper in Science by Quentin Atkinson, titled, "Phonemic Diversity Supports a Serial Founder Effect Model of Language Expansion from Africa" Atkinson:2011. This seems an inauspicious title, considering that the genetic version of the serial founder effect model has taken serious body blows this year. Here's the abstract:

Human genetic and phenotypic diversity declines with distance from Africa, as predicted by a serial founder effect in which successive population bottlenecks during range expansion progressively reduce diversity, underpinning support for an African origin of modern humans. Recent work suggests that a similar founder effect may operate on human culture and language. Here I show that the number of phonemes used in a global sample of 504 languages is also clinal and fits a serial foundereffect model of expansion from an inferred origin in Africa. This result, which is not explained by more recent demographic history, local language diversity, or statistical non-independence within language families, points to parallel mechanisms shaping genetic and linguistic diversity and supports an African origin of modern human languages.

The data in the paper demonstrate a correlation between the phoneme inventory of languages and their geographic region, with areas furthest from Africa (Oceania and South America) having languages that average fewer distinct sounds. As in the case of genetics, this could be explained by other histories besides a recent serial founder effect.

But for historical linguistics, there's a separate problem that deserves some consideration: Why should the origin of languages have had the largest inventory of phonemes? If small populations typically lose phonemic variation, why would sparse hunter-gatherer populations of Africa have built up the largest store of sounds just as they were getting started talking?

Atkinson suggests that African populations have had more time to recover diversity after a bottleneck at the origin of language. That seems an inauspicious suggestion, considering that the genetic model of a founding bottleneck in Africa has taken some serious body blows this year.

Just sayin'...