In Mandarin Chinese, for example, the syllable "ma" can take on several unique meanings.
When it's pronounced with a single high-pitched tone, "ma" means "mother."
But when it has a low-pitched lilt in the middle, it means "horse"—making it a word you don't want to mispronounce.
The other half of all languages are nontonal, meaning they use pitch only for things like marking a question.
If your ancestors were from Southeast Asia or sub-Saharan Africa, where the native languages are nearly all tonal, you probably have the older versions of both genes.
If your ancestors were all from Europe, where people mostly speak nontonal languages, you probably have the new version of Microcephalin and have a 50-50 chance of carrying the new ASPM gene.
These genes may give you a bit of a tin ear for tone, the study suggests.
(Related: "India Acquired Language, Not Genes, From West, Study Says" [January 10, 2006].)
The effects of these genetic markers might not be obvious in babies learning their native tongues.
As far as anyone has been able to tell, babies can learn any language on Earth equally easily, as long as they are exposed to it from a very early age.
But the differences could show up more strongly in adults struggling to learn a foreign language.
Also, small differences created as children learn languages can add up over time to transform the way societies communicate.
"Children don't have quite the same language that their parents have," Ladd said. That's why Shakespeare's English is different from today's.
The new study suggests that genes could also play a role in this phenomenon.
"If there was really a gene for tone, you would expect even native speakers of a tone language to vary greatly in terms of their abilities to perceive or use tones in their languages," said Suzanne Flynn, a linguist at the Massachusetts Institute of Technology in Cambridge.
Ladd plans to look for this kind of effect in follow-up studies.
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