Die inzwischen erschienene Literatur zu den genannten Forschungen über die Evolution nicht-tonaler Sprachen (Stud. gen.) enthält noch mancherlei spannende Details. Im National Geographic erklärt Robert Ladd kurz und knapp wie er auf die Hypothese kam:
"I looked at maps of the distributions of the old and new versions of the genes," Ladd said. "And I said, that looks like the distribution of tonal languages."Und Wissenschaftsjournalist Michael Balter erklärt es in "Science" noch einmal ganz gut:
Taking genetic data from 49 populations worldwide, Dediu and Ladd searched for correlations between 983 genetic variants, including ASPM-D and microcephalin-D , and 26 features of the languages spoken by the populations, including the number of consonants and the use of inflections or tones. There was little overall correlation, meaning that most of these language differences are unlikely to be affected by genetics.Robert Ladd sagt dann als Antwort auf dem Wissenschafts-Blog von Mark Libermann noch weitere spannende Dinge. Da heißt es zunächst:
In the case of ASPM-D and microcephalin-D , however, there was a highly significant correlation between possession of these variants and speaking a nontonal language, even after the researchers made statistical corrections for the effects of shared linguistic histories. (...) Bruce Lahn, a geneticist at the University of Chicago in Illinois whose team first identified ASPM-D and microcephalin-D , says that the "work is obviously highly significant if confirmed." Nevertheless, Lahn says, the authors still need to rule out other possible explanations for their results.
"Our work is really hypothesis-generating rather than hypothesis-testing."Und er erläutert die Entwicklung der Hypothese als Antwort auf die Kritik von Mark Libermann weiterhin folgendermaßen:
"Mark is right that our original hypothesis was not much more than a hunch based on human pattern recognition abilities. (Several referees said similar things on our way to publication.) Specifically, this project began in earnest when I pattern-recognized a connection between the Lahn group's gene maps and my mental map of the distribution of tone languages. But I have been thinking for some time about the cognitive status of tone, paralanguage and other non-sequential linguistic features (... ); Dan's PhD research, starting from entirely different premises based on evolutionary genetics and the study of human prehistory, was looking for evidence of gene-language correlations of exactly the sort we've documented; and of course, we knew that ASPM and Microcephalin are involved in brain development. So if it was a hunch, it was a reasonably well-grounded hunch."Und dann folgen noch weitere Erläuterungen zu den Gründen für die bisherige Vorgehensweise:
"Now, it's certainly true, as Mark says, that our geographical correlations would mean more if they had proceeded from some experimental demonstration of some sort of genetically linked, language-related, cognitive/behavioral/perceptual difference. But given the widespread assumption (rooted in the Boasian tradition, but with a significant contemporary boost from Chomsky) that the human language faculty is absolutely uniform across the species, it's very unlikely that we would have been able to get funding to look for such a difference first. So we started by doing something we could do on our own without such support, namely testing the apparent correlation. Having done that, we hope we are now in a better position to apply for funding for the expensive part of the research. This might seem backwards, but it's a pretty common way of doing genetic mapping studies: start from your phenotype, use correlational studies to identify plausibly associated genetic markers, and then try to understand experimentally what the genetic markers actually do."Das Thema wurde bisher in drei Beiträgen auf "Studium generale" behandelt (1, 2, 3)
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