It's no monkey's business

In my formative years in the English Midlands, I played cricket at Twycross every summer. This Leicestershire-Warwickshire border village is home to one of the UK's most famous zoos and, before such things were frowned upon, their chimpanzees appeared in all sorts of entertainments.

Most notable was a long-running series of commercials for a popular brand of tea. Some of the things the apes were made to do were preposterous, but their dexterity and intelligence was not up for question. They probably just needed a better agent.

Much stronger than humans pound-for-pound, their physical strength wasn't up for question either. Never once, however, did a Twycross chimp make it into the village cricket XI. They could probably hold a bat, but running, fielding and bowling would have been completely beyond them. Our closest living relatives were entrusted with tea, and tea alone.

Why is it, then, that Homo sapiens is so good at flinging down a ball at high speed, and Pan troglodytes so rubbish? To investigate this, we need to delve into evolutionary physiology, and a new study led by Dr Neil Roach of George Washington University has helped shed some very interesting light on the matter.

As international batsmen well know, humans can throw accurately at speeds in excess of 100mph. Chimps can barely muster a fifth of that velocity and with much lower precision. Together with colleagues from Harvard University, and the National Centre for Biological Sciences in Bangalore, Dr Roach compared the two species' body structure, investigated what it is that enables humans to throw so fast, and then looked at the fossil record of those features.

As you might imagine, the shoulder is important. Just how important was demonstrated when Roach and colleagues tested the throwing capacity of baseball pitchers. The pitchers were forced to wear therapeutic shoulder braces that constrained the rotational range of movement; this reduced their throwing speed by between 2% and 14%.

Though a mobile, muscular shoulder is very important, it's not the whole story. Roach argues that the storage and release of elastic energy is just as - if not more - crucial. The extremely rapid internal rotation of the upper arm bone is then powered by a combination of cocking the arm at the same time as taking a large forward step.

Of course, this is fine for baseball pitchers, since they can use their elbow flex. Studies by other researchers indicate that this is the second most important generator of throwing speed. Legally at least, cricketers do not have that luxury, so how is it that fast bowlers aren't that much slower than the fastest baseball pitchers?

"Cricket bowling is fascinating," Roach tells me. "I actually started studying the bowling motion before transitioning to pitching.

"The restriction imposed on cricket bowlers requiring them to keep a straightened, extended elbow through the throw does reduce their throwing performance," he notes. "However, cricket bowlers compensate for this reduction by using a run-up."

In laboratory experiments, Roach disallowed cricket bowlers from running in.

"If you force them into a baseball pitching stance, their performance drops significantly. So I guess the simple answer is, the elbow is important to throwing velocity, but cricket bowlers get around this performance reduction by improving throwing speed with a run-up."

To go back to our non-fast-bowling cousins, it transpires that we humans have three key advantages over chimps. Firstly, our mobile waist provides more torso rotation. Secondly, the twisting of our upper arm bone takes place at a lower angle, giving a greater range of motion. Thirdly, we have a more laterally oriented shoulder joint. This aligns the flexure of the pectoral muscles with the rotation of the torso, giving a greater moment of inertia to the arm.

Since humans and chimps diverged at least five million years ago, the next question is when we acquired these specific features. To explore this, Roach's team examined the fossil record of our tribe - the hominins - to see who the first fast throwers might have been.

Australopithecus, which lived in Africa between about four and two million years ago, appears to have had some of the required skeletal characters, such as a flexible waist and a low torsion of the upper arm bone, but not all.

Upright Man was a different matter, though. The skeletons of Homo erectus show he had hyperextendable wrists, so would almost certainly have been capable of spin bowling. Roach, however, thinks everything was in place for speed too. Other experts disagree, but can it be a coincidence that fossils of Homo erectus have been found in England, India and Sri Lanka?

More seriously, though, why were these evolutionary traits so useful? A selective advantage in hunting may have been the key.

Hominins have been eating meat for more than two million years. Developing an ability to throw well was not necessarily for killing prey - at least to start with - but perhaps in defending carcasses, or scavenging them from other animals better equipped with fangs and claws. If the first lbw was lion-before-wildebeest, an accurate quickie would have been crucial to earning dismissals. We were fast-food bowlers to begin with.

As to what we were bowling, the fossil record is rather harder to decipher. The earliest projectiles would have almost certainly been rocks, and it's pretty much impossible to distinguish between a thrown rock and a non-thrown rock. The first unequivocal thrown artefacts appear much later on, and the fossil record of cricket balls is barely worth writing about.

So, millennia down the line, our ability to throw fast remains, but we perhaps no longer use it so wisely. Stone Age hunters almost certainly threw less often than top-level fast bowlers, who seem to break down with alarming frequency. Flintstone would never have suffered the burnout that Flintoff did.

Maybe it would be humane to develop a selective breeding programme using the least injury-prone fast bowlers. There must be a limit on the speed that any cricketer can bowl at, though, especially if accuracy is to be retained. Can anyone exceed Shoaib Akhtar's record-breaking pace?

"I don't have a great answer," admits Roach. "My suspicion is that the demands of storing elastic energy to produce 90-100mph throws are significant enough that the tendons and ligaments crossing the shoulder probably can't handle much more.

"It is possible that you will see more athletes throwing 100mph in the future," he concludes, "but that will probably come at the cost of more injuries. I think it is highly unlikely that batters would be facing 120mph bowlers in the future."

And barring a very long-term Twycross breeding programme, it's even less likely that they'll be facing any 120mph chimpanzees.