Researcherssay they have the first good evidence that genes play a significant role inchimp handedness, just as they are believed to in humans. They also saythat--as in humans--left-handedness is often associated with developmentalanomalies.

Anything left? A chimp digs for peanut butter.
CREDIT: YERKES

　　WilliamHopkins and colleagues at the Yerkes Regional Primate Research Center inAtlanta determined handedness by watching chimps scoop peanut butter out of atube. They then measured similarity in hand preferences between mothers andoffspring in 134 family pairs.

　　Theresearchers report in the 4 July issue of Psychological Science thatbirth order had a major effect on handedness in this group, as well as in 155pairs of maternal half-siblings (siblings who share the same mother). Theyclassified first-born chimps and those born sixth or later as being at highrisk for "developmental instability"--a term for various prenatalperturbations such as hormonal irregularities associated with both firstpregnancies and late ones. These conditions seemed to make left-handedness morelikely, even when the mother was right-handed: The team found that among thelow-risk pairs, 86% of the offspring of right-handed females were right-handed;among the high-risk ones, the proportion was only 46%.

　　It appears,says Hopkins, that "right-handedness is the ‘norm’ " and that"at least some left-handedness may be due to pathological events"around or before birth. Understanding chimp handedness "may provideinsights into ... allegedly unique human psychological functions," theresearchers write.

　　But at leastone researcher, Greg Westergaard, who runs a monkey colony at LABS of Virginiain Yemassee, South Carolina, believes the findings raise the opposite question:"Given the relatively recent split between humans and apes, why are humansso much different?" he asks. Only 10% to 15% of humans are left-handed,compared with one-third of Yerkes chimps and even more of those in thewild--which suggests that there is very little specialization between the twohemispheres of the brain in chimps compared with humans.

摘自：science.now