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1、NO1:This morning I want to tell you about a recent scientific discovery dealing with the relationship between plants and animals. This is about a desert shrub whose leaves can shoot a stream of poisonous resin a distance of six feet. You think it would be safe from all attacks by insects? But a rece
2、nt study has found one insect, a beetle that can chew its way past the plants defense system by cutting the main vein that delivers the poison to the leaves. This vein cutting is just one method the beetles used to prepare a safe meal. Another is by cutting a path all the way across the leaves to ho
3、ld the flow of chemicals. Then they simply eat between the veins of poison. In the past, scientists who studied insect adaptation to plant defenses have focused on chemical responses. That is, how the insects can neutralize or alter the poisonous substances plants produce. Whats unique about this ch
4、ewing strategy is that the beetle is actually exhibiting a behavioral response to the plants defenses rather than the more common chemical response. It is only after a beetles survived several encounters with the plants resin that it learns how to avoid the poison: by chewing through the resin trans
5、porting veins on the next leaf it eats. And thus gives itself a safe meal. However, it can take a beetle an hour and a half of careful vein cutting to prepare a small leaf that takes it only a few minutes to eat. So, though the method is effective, its not very efficient. NO2:Human populations near
6、the equator have evolved dark skin over many generations because of exposure to the fiercest rays of the sun. A similar phenomenon has also occurred in other parts of the animal kingdom. The African grass mouse is a good example. Most mice are nocturnal, but the African grass mouse is active during
7、daylight hours. This means that it spends its days searching for food in the semi-dry bush in scrubby habitats of eastern and southern Africa. Its furry stripes like a chipmunks, which helps it blend in with its environment. Because it spends a lot of time in the intense tropical sun, the grass mous
8、e has also evolved two separate safeguards against the suns ultraviolet radiation. First, like the population of humans in this region of the world, the skin of the grass mouse contains lots of melanin, or dark pigment. Second and quite unusual, this mouse has a layer of melanin-pigmented tissue bet
9、ween its skull and skin. This unique cap provides an extra measure of protection for the grass mouse and three other types of African mouse, like rodents that are active during the day. The only other species scientists has identified with the same sort of skull adaptation is the white tent-making b
10、at of the Central American tropics. Although these bats sleep during the day, they do so curled up with their heads exposed to the sun. NO3:Weve been looking at fear from a biological perspective, and someone asked whether the tendency to be fearful is genetic. What some studies done with mice indic
11、ate that mammals do inherit fearfulness to some degree. In one study, for instance, a group of mice was placed in a brightly lit open box with no hiding place. Some of the mice wandered around the box and didnt appear to be bothered about being so exposed. But other mice didnt move. They stayed up a
12、gainst one wall which indicated that they were afraid. Well, when fearful mice, or you might say anxious mice like the ones who stayed in one place, when mice like these were bred with one another repeatedly, after about twelve or so generations, then all of the offspring showed similar signs of fea
13、rfulness. And even when a new born mouse from this generation was raised by a mother and with other mice who were not fearful, that mouse still tended to be fearful as an adult. Now why is this? Well its thought that specific genes in an animals body have an influence on anxious behavior. These are
14、genes that are associated with particular nerve-cell receptors in the brain. And the degree of overall of fearfulness in the mammal seems to depend in large part on the presence or absence of these nerve-cell receptors. And this appears to apply to humans as well by the way. But while a tendency tow
15、ards anxiety and fear may well be an inherited trait, the specific form that the fear takes has more to do with the individuals environment. So a particular fear, like a fear of snakes or the fear of spider, say, is not genetic, but the overall tendency to have fearful responses, is. NO4:Lets turn o
16、ur focus now to advertising. We all know what an advertisement is: Its essentially a message that announces something for sale. Now theres an important precondition that must exist before you have advertising, and thats a large supply of consumer goods, that is, things to sell. You see in a place where the demand for a product is greater than the supply, there is no need to advertise. Now the earliest forms of advertising going back many hundreds of years with a simple sign ov
