Manyanimals seem able to treat their illnesses themselves. Humans way have a thingor two to learn from them.
A
For thepast decade Dr Engel, a lecturer m environmental sciences at Britain’s OpenUniversity, has been collating examples of self-medicating behaviorin wild animals. She recently published a book on the subject. In a talkat the Edinburgh Science Festival earlier this month, she explained that the ideathat animals can treat themselves has been regarded with some skepticism by hercolleagues in the past. But a growing number of animal behaviourists now thinkthat wild animals can and do deal with their own medical needs.
B
Oneexample of self-medication was discovered in 1987. Michael Huffman and MohamediSeifu, working in the Mahale Mountains National Park in Tanzania, noticed thatlocal chimpanzees suffering from intestinal worms would dose themselves withthe pith of a plant called Veronia. This plant produces poisonous chemicalscalled terpenes. Its pith contains a strong enough concentration to kill gutparasites, but not so strong as to kill chimps (nor people, for that matter;locals use the pith for the same purpose). Given that the plant is knownlocally as “goat-killer”, however, it seems that not all animals are as smartas chimps and humans. Some consume it indiscriminately,and succumb.
C
Sincethe Veronia-eating chimps were discovered, more evidence has emerged suggestingthat animals often eat things for medical rather than nutritional reasons. Manyspecies, for example, consume dirt-a behaviour known as geophagy ( 食土癖). Historically, the preferred explanation was that soil supplies mineralssuch as salt. But geophagy occurs in areas where the earth is not a usefulsource of minerals, and also in places where minerals can be more easilyobtained from certain plants that are known to be rich in them. Clearly,theanimals must be getting something else out of eating earth.
D
Thecurrent belief is that soil-and particularly the clay in it-helps to detoxifythe defensive poisons that some plants produce in an attempt to preventthemselves from being eaten. Evidence for the detoxifying nature of clay camein 1999, from an experiment carried out on macaws by James Gilardi and hiscolleagues at the University of California, Davis. Macaws eat seeds containingalkaloids, a group of chemicals that has some notoriously toxic members, suchas strychnine. In the wild, the birds are frequently seen perched on erodingriverbanks eating clay. Dr Gilardi fed one group of macaws a mixture of aharmless alkaloid and clay, and a second group just the alkaloid. Several hourslater, the macaws that had eaten the clay had 60% less alkaloid in theirbloodstreams than those that had not, suggesting that the hypothesis iscorrect.
E
Otherobservations also support the idea that clay is detoxifying. Towards thetropics the amount of toxic compounds in plants increases-and so does theamount of earth eaten by herbivores. Elephants lick clay from mud holes allyear round, except in September when they are bingeing on fruit which, becauseit has evolved to be eaten, is not toxic. And the addition of clay to the dietsof domestic cattle increases the amount of nutrients that they can absorb fromtheir food by 10-20%.
F
A thirdinstance of animal self-medication is the use of mechanical scours to get ridof gut parasites. In 1972 Richard Wrangham, a researcher at the Gombe StreamReserve in Tanzania, noticed that chimpanzees were eating the leaves of a treecalled Aspilia. The chimps chose the leaves carefully by testing them in theirmouths. Having chosen a leaf, a chimp would fold it into a fan and swallow it.Some of the chimps were noticed wrinkling their noses as they swallowed theseleaves, suggesting the experience was unpleasant. Later, undigested leaves werefound on the forest floor.
G
DrWrangham rightly guessed that the leaves had a medicinal purposethis was,indeed, one of the earliest interpretations of a behaviour pattern asself-medication. However, he guessed wrong about what the mechanism was. His(and everybody else’s) assumption was that Aspilia contained a drug, and thissparked more than two decades of phytochemical research to try to find out whatchemical the chimps were after. But by the 1990s, chimps across Africa had beenseen swallowing the leaves of 19 different species that seemed to have fewsuitable chemicals in common.The drug hypothesis was looking more and moredubious.
H
It wasDr Huffman who got to the bottom of the problem. He did so by watching whatcame out of the chimps, rather than concentrating on what went in. He foundthat the egested leaves were full of intestinal worms. The factor common to all19 species of leaves swallowed by the chimps was that they were covered withmicroscopic hooks. These caught the worms and dragged them from their lodgings.
I
Followingthat observation, Dr Engel is now particularly excited about how knowledge ofthe way that animals look after themselves could be used to improve the healthof livestock. People might also be able to learn a thing or two-and may,indeed, already have done so. Geophagy, for example, is a common behaviour inmany parts of the world. The medical stalls in African markets frequently selltablets made of different sorts of clays, appropriate to different medicalconditions.
J
Africansbrought to the Americas as slaves continued this tradition, which gave theirowners one more excuse to affect to despise them. Yet, as Dr Engel points out,Rwandan mountain gorillas eat a type of clay rather similar to kaolinitethemain ingredient of many patent medicines sold over the counter in the West fordigestive complaints. Dirt can sometimes be good for you, and to be “as sick asa parrot” may, after all, be a state to be desired.
答案：
14. TRUE15. NOT GIVEN 16. FALSE 17. FALSE
18. pith 19. Terpenes 20. Alkaloids 21. Detoxify 22. hooks
23. G 24. D 25. E 26. C
|Archiver|手机版|小黑屋|雅思托福英语全球网
( 闽ICP备14014910号 )
|
闽公网安备 35020302034732号
发表于 2022-9-6 16:07:45
QQ好友和群
QQ空间
腾讯微博
腾讯朋友
收藏