雅思阅读分析

For centuries, many scholars maintained that humans were the only intelligent organisms on Earth. Many traits were considered to be exclusively human examples of others - for example, language, tool use, deception, and awareness of self and others. However, new research on a number of animals, particularly birds, has called into question the uniqueness of these traits, forcing us to reconsider this opinion. In 1964, people were amazed when naturalist Jane Goodall discovered chimpanzees making and using tools. But ornithologists, first who study birds, were not overly surprised. Almost 20 years earlier, a researcher observed woodpecker finches on the Galapagos Islands. These tiny birds routinely used twigs to extract grubs from under bark.

Since then, the catalogue of tool-using animals has grown. At least three Australian bird species make tools similar to those of the woodpecker finch, and when white-winged choughs come across shellfish, they have been known to use rocks as hammers to crack open the recalcitrant shells. Other birds show a more sophisticated level of insight. For example, black kites have been reported dropping bait into lakes to bring fish to the surface, thereby making them easier to catch. A kite may also pick up a smouldering stick from an area recently burned by a bushfire and drop the stick on a patch of unburned grass. The bird then feasts on the small animals that flee from the subsequent fire.

Most tool-using behaviours are a means of extracting food, which may provide a clue as to how the mental abilities needed for tool use evolved. The predominant explanation is based on the proverb that 'necessity is the mother of invention'. Essentially, brain tissue is energetically expensive, so animals should have evolved only the intellectual capabilities required to overcome the challenges they face in their environment. Consider a hypothetical duck grazing on a seemingly endless supply of grass. Being particularly intelligent will not help the duck eat more grass. In contrast, other species, such as birds of prey, live in a more challenging environment, where food may be distributed erratically, hidden from view or highly mobile. The food itself may be quite intelligent. So if there are not enough resources to feed all individuals, then only the smartest in each generation will live and reproduce.

New Caledonian crows boast many different tools in their toolkit. They use a hooked tool made by removing all but one of the side branches from a twig. They fashion serrated rakes (using their beaks as scissors) from stiff, leathery pandanus leaves. They also make probes by modifying their own molted feathers. Each tool is used in slightly different ways to pull grubs from deep within tree trunks. The crows carry their favourite tool from one foraging site to the next. They also store their tools for later reuse in a secure place on their perch. Problem-solving abilities have traditionally been thought to be beyond the reach of animals. Nevertheless, birds are coming up with innovative solutions all the time. Recently, New Caledonian crows were observed moulding a piece of wire, something they had never seen before, into a hook and then using it to retrieve food.

Literally hundreds of such reports have accumulated in back copies of scientific journals. Recently, a team of biologists from McGill University in Canada collated them and compared the frequency and size of innovations with the size of the birds' forebrain (the brain area responsible for higher-order information processing) relative to forebrain. The team uncovered a clear relationship: birds with relatively large forebrains are able to invent fresh solutions to ecological challenges, and to exploit the discoveries and inventions of others, more often than birds with relatively small forebrains.

Intelligence in birds may also arise as a result of selection to overcome the dynamic challenges of communal living. Since this involves competition between group members, as well as cooperation, animals may need to be able to reflect on their own intentions to be successful in a social. The consequence of being part of a community may be the evolution of a distinctly 'political' brain.

What better way to exercise a 'political' brain than to be deceitful? Perhaps the best example of deception among birds comes from the white-winged choughs. Choughs are cooperative breeders - that is, they form a communal group consisting of one breeding pair and up to 15 non-breeding 'helpers'. However, because young choughs have so little enthusiasm for foraging, or gathering food, they are often too hungry to help. And because it is socially unacceptable to be part of a group and not contribute, young choughs will often act deceptively. For example, when an adult is watching, a young chough will pretend to look for food in the ground. Instead, it waits until the adult departs and then eats the food itself. A chough can also help another bird by preening the chicks. Interestingly, it is more likely to preen the chicks if the group can see it doing so. A chough that has been sitting totally still on the nest while the rest of the group is foraging out of sight will immediately spring into frantic activity as soon as some of its group members come into view. It is likely that these young choughs are only motivated to help when others are watching because they are concerned about their social status. Choughs need other choughs to like them, as they cannot breed without them.