NEW YORK >> It’s a big year for throwing. The greatest closer in baseball history, Mariano Rivera of the Yankees, is retiring. Aroldis Chapman, the overpowering Cincinnati Reds reliever, continues to fire fastballs beyond 100 mph.

And now some scientists say they’ve figured out when our human ancestors first started throwing with accuracy and fire power, as only people can: Nearly 2 million years ago.

That’s what researchers conclude in a study released Wednesday by the journal Nature. There’s plenty of skepticism about their conclusion. But the new paper contends that this throwing ability probably helped our ancient ancestor Homo erectus hunt, allowing him to toss weapons — probably rocks and sharpened wooden spears.

The human throwing ability is unique. Not even a chimp, our closest living relative and a creature noted for strength, can throw nearly as fast as a 12-year-old Little Leaguer, says lead study author Neil Roach of George Washington University.

To find out how humans developed this ability, Roach and co-authors analyzed the throwing motions of 20 collegiate baseball players. Sometimes the players wore braces to mimic the anatomy of human ancestors, to see how anatomical changes affected throwing ability.

The human secret to throwing, the researchers propose, is that when the arm is cocked, it stores energy by stretching tendons, ligaments and muscles crossing the shoulder. It’s like pulling back on a slingshot. Releasing that “elastic energy” makes the arm whip forward to make the throw.

That trick, in turn, was made possible by three anatomical changes in human evolution that affected the waist, shoulders and arms, the researchers concluded. And Homo erectus, which appeared about 2 million years ago, is the first ancient relative to combine those three changes, they said.

But others think the throwing ability must have appeared sometime later in human evolution.

Susan Larson, an anatomist at Stony Brook University in New York who didn’t participate in the study, said the paper is the first to claim that elastic energy storage occurs in arms, rather than just in legs. The bouncing gait of a kangaroo is due to that phenomenon, she said, and the human Achilles tendon stores energy to help people walk.

The new analysis offers good evidence that the shoulder is storing elastic energy, even though the shoulder doesn’t have the long tendons that do that job in legs, she said. So maybe other tissues can do it too, she said.

But Larson, an expert on evolution of the human shoulder, said she does not think Homo erectus could throw like a modern human. She said she believes its shoulders were too narrow and that the orientation of the shoulder joint on the body would make overhand throwing “more or less impossible.”

Rick Potts, director of the human origins program at the Smithsonian Institution, said he is “not at all convinced” by the paper’s argument about when and why throwing appeared.

The authors did not present any data to counter Larson’s published work that indicates the erectus shoulder was ill-suited for throwing, he said.

And it is “a stretch” to say that throwing would give erectus an advantage in hunting, Potts said. Large animals have to be pierced in specific spots for a kill, which would seem to require more accuracy than one could expect erectus to achieve from a distance, he said.

Potts noted that the earliest known spears, which date from about 400,000 years ago, were used for thrusting rather than throwing.

___ Online:

Nature: http://www.nature.com/nature