Reuters:

Chimpanzees scampering on a treadmill have provided support for the notion that ancient human ancestors began walking on two legs because it used less energy than quadrupedal knuckle-walking, scientists said…

The chimpanzees were taught to walk on the treadmill both quadrupedally and bipedally, the scientists said.

“These guys are smart enough that they would hit the stop button on the treadmill when they were done. If they didn’t want to walk on the treadmill, they’d just hit the stop button or they’d jump off,” [University of Arizona anthropologist David] Raichlen said…

Wait a second.  Where did our ancient human ancestors get all the necessary treadmills? They must have needed tens of thousands of them to enable all of the then wanna-be bipedallers to get the required amount of upright walking practice?