雅思阅读真题+题目+答案：Two Wings and a Kit-box
A Many animals use tools, but tool manufacture is rare. Rarer still is cumulative change in tool manufacture. Chimpanzee and orangutan tool manufacture, for example, is often haphazard, and their tools show no evidence of incremental improvements over time. In contrast, current human technology is the result of a long series of cumulative changes. The "ratchet-like" nature of this technological evolution means that design changes are retained at the population level until new, improved designs arise. This ratchet effect is possible because tool manufacture methods are socially transmitted with sufficient fidelity that individuals do not need to reinvent or recapitulate past inefficient designs. The skills required for the development of this cumulative technology are claimed to include high-fidelity social learning, an understanding of physical relationships and functional properties of objects, and the ability for fine object manipulation. Animals other than humans are generally presumed to lack the necessary neural hardware and cognitive sophistication for cumulative technological evolution.
B The New Caledonian crow, Corvus moneduloides, is an ideal model species to examine the links between tool manufacture, social learning and cognition. These crows make tools out of the twigs and the long, prickly edges of the leaves of the tropical pandanus tree to facilitate the capture of invertebrates, says New Zealander Gavin Hunt. He studies these crows, which live on islands between Australia and Fiji. Dr. Hunt has discovered that New Caledonian crows have three different designs for tools. They also make two kinds of stick tools-hooked and not hooked. The manufacture of pandanus tools provides a unique opportunity for study because a record of tool manufacture is faithfully recorded in "counterparts" or outlines remaining on the leaf edges. In the wild, adult New Caledonian crows sever long narrow pandanus (a stilt-rooted palm native to Southeast Asia) leaves and split them to keep the sharply serrated outside edge intact. The split leaves are cut again in roughly 8 lengths for billcontrolled tools to hook small insects from cracks or to swish rapidly through leaf litter to impale other prey.
C Recent work has revealed that these tools have four features previously thought to be unique to primitive humans: a high degree of standardisation, the use of hooks, "handedness," and cumulative changes in tool design. Evidence has been discovered of cumulative changes in a field survey documenting the shapes of 5,550 tools from 21 sites throughout the range of pandanus tools. Three distinct tool designs are found: wide tools, narrow tools, and stepped tools. The lack of ecological correlates of the different tool designs and their geographic overlap make it unlikely that they evolved independently. Similarities in the method of manufacture for each design suggest that pandanus tools have gone through a process of cumulative change from a common historical origin.
D Evidence is accumulating quickly on the inherent talent of crow's toolmaking ability which indicates that this ability is at least partly inherited and not dependent on learning through social contacts. To date there is only circumstantial evidence that New Caledonian crows transmit tool-making knowledge via social learning. These crows live in small family units where juveniles have ample opportunity to learn foraging techniques. The social learning and reasoning abilities of other Corvus species are well documented. The high fidelity in the shape of tool design at sites makes individual trial-anderror learning unlikely. Similarly, the evidence that crows might have some grasp of the functional properties of their tools is also only inferential.
E Researchers have also found that crows use different sides of their beaks to make and use tools. This suggests that different parts of the brain may control making and using tools, and that the biology of handedness—or beakedness— may be more complex than we thought.」ust like humans, New Caledonian crows are usually right "handed" when it comes to tasks such as making tools.But it turns out the birds use their tools with left and right sides equally, although individual crows prefer one side or the other. "This has opened up Pandora's box," says William McGrew, who studies chimpanzees' tool use at Miami University. "People always assumed handedness would be the same for using and making tools." Scientists will now be more wary of making this assumption, he adds.
F A major breakthrough in these studies occurred when it became evident that traditional theory of brain evolution as espoused by Ludwig Edinger, a neurobiologist and the leading comparative anatomist of a hundred years ago, was wrong. He believed that brains evolved in a straight line with invertebrates at the low end and progressed upwards through fish, reptiles, birds, to mammals, with humans at the top. Neurobiologists now understand that bird brains, although constructed differently from that of mammals, nonetheless function as elegantly as any mammals' brain. In fact, in proportion to body size, a crow's brain is as large as a chimpanzee's.
G In mammals, the lower third of our brains consists of groups of neurons, whereas the upper two thirds there exists neo-cortexes made up of flat cells, six cell layers thick. The top part generates our rational or intellectual activity, whereas the bottom third controls our instinctive reactions such as extending an arm to soften a fall or jerking away a hand when touching something hot. In human evolution the six cell-layered sheet on the top of the brain spread to such an extent that the only way the scull-confined brain could contain its increased area was for it to become convoluted, i.e. with many folds and crevices. The tops of bird brains are smooth, not folded, and until recently were thought to consist of cells grouped in clusters similar to the lower part of mammal brains, and thus would make all bird behaviour merely instinctive. We know now this is not the case, but the exact neural pathways are still unclear. What seems to have happened is an example of convergent evolution of intelligence where two differing forms of brain structure eventually lead to almost equivalent brain power. "New Caledonian crows teach us that in many ways other animals are not so different from us, and we should respect them for their differences and similarities," says Hunt.
Look at the following diagrams A-F.
Match the correct diagram to each tool manufactured by the New Caledonian crow.