60秒科学:大象能负重的原因（在线收听）

大多数四条腿动物用后腿前进，前腿停步，而研究表明，大象用四条腿来加速和“刹车”。

Elephants. They’re the SUVs of the animal kingdom. They’re big and rugged, and can carry lots of cargo. And now a study in the Proceedings of the National Academy of Sciences  suggests they come equipped with the quadruped version of all-wheel drive.

When it comes to locomotion, elephants are not exactly fleet of foot. And they seem to hold their legs straighter than other animals do, at least when they walk. So scientists [John R. Hutchinson et al] set out to examine more closely how elephant limbs mechanically move all that mass around.

Six Asian elephants walked or ran over a sidewalk equipped with pressure sensors, as the scientists used high-speed infrared video cameras to monitor their gait. And they found that elephant legs actually do bend enough to provide significant leverage when on the move. More surprising is that pachyderms’ front and rear legs are on equal footing when it comes to acceleration and braking. All other four-legged animals, like dogs or cats or horses, divvy up those duties. With their rear legs powering the push forward, and their front legs acting as brakes.

That arrangement lets elephants trade speed for stability. Sadly, it does nothing for their fuel economy. Of course, they do have the roomiest trunk.

—Karen Hopkin