Questions 6-10An article published recently in the prestigious scientific journal Nature is shedding new light on an important, but hitherto little has been appreciated, aspect of human evolution. In this article, Professors Dennis Bramble and Daniel Lieberman suggest that the ability to run was a crucial factor in the development of our species. According to the two scientists, humans possess a number of anatomical features that make them surprisingly good runners. ’We are very confident that p selection for running-which came at the expense of the historical ability to live in trees-was instrumental in the origin of the modern human body form,’ says Bramble, a biology professor at the University of Utah.Traditional thinking up to now has been that the distinctive, upright body form of modern humans has come about as a result of the ability to walk, and that running is simply a by-product of walking. Furthermore, humans have usually been regarded as poor runners compared to such animals as dogs, horses or antelopes. However, this is only true if we consider fast running, or sprinting, over short distances. Even an Olympic athlete can hardly run as fast as a horse can gallop, and can only keep up a top speed for fifteen seconds or so. Horses, antelopes and greyhounds, on the other hand, can run at top speed for several minutes, clearly outperforming us in this respect. But when it comes to long-distance running, humans do astonishingly well. They can maintain a steady pace for miles, and their overall speed compares favourably with that of horses or dogs.Bramble and Lieberman examined twenty-six anatomical features found in humans. One of the most interesting of these is the nuchal ligament, a band of tissue that extends from a ridge on the base of the skull to the spine. When we run, it is this ligament that prevents our head from pitching back and forth or from side to side. Therefore, we are able to run with steady heads, held high. The nuchal ligament is not found in any other surviving primates, although the fossil record shows that Homo erectus, an early human species that walked upright, much as we do, also had one. Then there are our Achilles tendons at the backs of our legs, which connect our calf muscles to our heel bones-and which have nothing to do with walking. When we run, these tendons behave like springs, helping to propel us forward. Furthermore, we have low, wide shoulders, virtually disconnected from our skulls, another anatomical adaptation which allows us to run more efficiently. Add to this our light forearms, which swing out of phase with the movement of our legs to assist balance, and one begins to appreciate the point that Bramble and Lieberman are trying to make.But what evolutionary advantage is gained from being good long-distance runners One hypothesis is that this ability may have permitted early humans to obtain food more effectively. ’What these features and fossil facts appear to be telling us is that running evolved in order for our direct ancestors to compete with other carnivores for access to the protein needed to grow the big brains that we enjoy today,’ says Lieberman.

The passage suggests that _______.

A． we do not need calf muscles in order to walk

B．without shoulders we could not run very fast

C．the movement of our forearms is out of phase

D．our Achilles tendons are an adaptation for running