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TPO51 生物学实验重做

Biology Experiment Reproduction

Listen to part of a conversation between a student and her biology professor.

Professor：So, the assignment is to reproduce one of the animal camouflage experiments we read about in our textbook. Which experiment did you pick?

Student:Well, I was wondering if I can try to reproduce an experiment that’s……kind of the opposite of what was discussed in the textbook?

Professor:So instead of how and why an animal might hide itself, you want to do something about why an animal might want to be seen? Em? Tell me more.

Student:Well, I got the idea from one of the journals you said we should look at. It’s an experiment about ah……they called them eyes bugs in the article?

Professor:Eyes bugs, sure. The patterns on the wings of moths and butterflies that are generally believed to scare off predators because they look like big eyes?

Student:Yeah. Except the article was about the experiment that disputes that theory.

Professor:Well, we know that the markings do scare the birds but the idea that the spots looked like eyes is……well, that is just a commonly held belief.

Student:So, that’s not even based on research?

Professor:Well, this whole idea of moths and butterfly markings being scary because they looked like eyes, rest on how we imagine the predators, like birds, perceive the markings. And we can never really know that. All we can do is observe bird behavior. But tell me more about the experiment.

Student:Ok. It said the experiment looked at the shapes of the markings on moths’ wings. The researchers wanted to know if the markings that were round and eye-shaped were more effective in deterring predators than square and rectangular markings.

Professor:Ok.

Student:Yeah. So they attached food to paper models of moths with different shaped marks drawn on the wings to see how birds reacted. And what’s interesting is they realized the round marks were not more effective in scaring bird than other shapes.

Professor:Were they less effective?

Student:No, they were about the same. But what researchers did determine is that larger markings were more effective than smaller markings in scaring off prey. They call this phenomenon “visual aliveness”.

Professor:Visual aliveness. Um. Well, I guess that it is not all that shocking if you think about it.

Student:So anyway, is it ok? Can I repeat this experiment and write about it?

Professor:Yes,I think that’ll work. The problem I proceed is……well……where? This is an urban campus, you’ll have a hard time finding a good place to set up the experiment.

Student:Oh, I wasn’t planning on doing it on campus. I’m going home for spring break and my family lives in the country, far from the near city. I can set it up in the backyard.

Professor:Good idea. Except one week is not a lot of time, so you will need to make some adjustments to have enough data. I’d set up the experiment near bird feeder and get in as much observation time as you can.

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TPO51 玉米和大刍草

Maize And Teosinte

Listen to part of a lecture in a botany class.

Professor:So, continuing with crop domestication and corn, or, um, maize as is often called, obviously it’s one of the world’s most important crops today. It’s such a big part of the diet in so many countries and it’s got so many different uses that it’s hard to imagine a world without it. But because it doesn’t grow naturally, without human cultivation, and because there’s no obvious wild relative of maize, um, well, for the longest time researchers weren’t able to find any clear link between maize and other living plants. And that’s made it hard for them to trace the history of maize.

Now, scientific theories about the origins of maize first started coming out in the 1930s, one involved a plant called teosinte.Teosinte is a tall grass that grows wild in certain parts of Mexico and Guatemala. When researchers first started looking at wild teosinte plants, they thought there was a chance that the two plants, um, maize and teosinte, were related. The young wild teosinte plant looks a lot like the corn plant. And the plants continue to resemble each other, at least superficially, even when they’re developed.

But when the scientists examined the fruits of the two plants, it was a different story.When you look at right corn, you see roll upon roll of juicy kernels, um, all those tiny little yellow squares that people eat. Fully-grown teosinte, on the other hand, has a skinny stock that holds only a dozen or so kernels behind a hard, um, almost a stone-like casing. In fact, based on the appearance of its fruit, teosinte was initially considered to be a closer relative to rice than to maize.

But there was one geneticist, named George Beadle, who didn’t give up so easily on the idea that teosinte might be, well, the parent of corn. While still a student in the 1930s, Beadle actually found that the two plants have very similar chromosomes, very similar genetic information. In fact, he was even able to make fertile hybrids between the two plants. In hybridization you remember, the genes of two species of plants are mixed to produce a new third plant, a hybrid. And if this offspring, this hybrid, is fertile, then that suggests that the two species are closely related genetically. This new hybrid plant looked like an intermediate, right between maize and teosinte. So Beadle concluded that maize must have been developed over many years, ah, that is a domesticated form of teosinte.

Many experts in the scientific community, however, remained unconvinced by his conclusions. They believed that with so many apparent differences between the two plants, it would have been unlikely that ancient, the pre-historic peoples could have domesticated maize from teosinte. I mean, when you think about it, these people lived in small groups, and they had to be on the move constantly as the seasons changed. So for them to selectively breed, to have the patience to be able to pick out just the right plants and gradually over generations, separate out the durable nutritious maize plant from the Beadle teosinte that easily broke apart, it’s a pretty impressive feat.

And you can easily see why so many experts would have been skeptical. But as it turns out, Beadle found even more evidence for his theory when he continued his experiments, producing new hybrids, to investigate the genetic relationship between teosinte and maize. Through these successful experiments, he calculated that only about 5 specific genes were responsible for the main differences between teosinte and maize. The plants were otherwise surprisingly similar, genetically.

And more recently, botanists have used modern DNA testing to scan plant samples collected from throughout the western hemisphere. This has allowed them to pinpoint where the domestication of maize most likely took place. And their research took them to a particular river valley in southern Mexico. They’ve also been able to estimate that the domestication of maize most likely occurred about 9000 years ago. And subsequent archaeological digs have confirmed this estimate. In one site, archaeologists uncovered a set of tools that were nearly 9000 years old. And these tools were covered with a dusty residue, a residue of maize as it turns out. Thus making them the oldest physical evidence of maize that we found so far.

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TPO51 计数系统的传播

The Transmission Of A Number System

Listen to part of a lecture in a world history class.

Professor:So one of the more common topics that comes up in world history because it’s had a pretty dramatic effect on how different societies evolved over long periods of time is cultural diffusion. Now, cultural diffusion is generally defined as the transmission of culture from one society to another. And by culture, we mean anything from artistic styles to……um……you know, technology, science. So we use culture very broadly. A common means of this process taking place is trade, travelling merchants or trading hubs, places where people from various areas all come together and ideas get exchanged.

Let’s start with the example of the transmission of a number system, a system that used the number Zero, from South Asia into Western Europe.

Ok, so before this cultural diffusion happened, the dominant number system in Western Europe was the Roman Numeral System. The Roman Numeral System developed primarily as a means of record-keeping, as a way to keep track of commercial transactions, um, taxes, censors’ records, things of that sort. As a consequence, this system started with the number One.

Student:With One? Not with Zero?

Professor:Right. See in Roman Numerals, Zero isn’t really a value in and out itself. It wasn’t used independently as a number on its own. If your primary concerns just basic types of record-keeping……

Student:Oh, yeah. I guess you wouldn’t need a Zero to count livestock.

Professor:Or to keep track of green production or do a census. And it wasn’t an impediment as far as sort of basic engineering was concerned either, um, to their ability to construct buildings, roads, stuff like that.

But other number systems developed in Asia, systems that do incorporate Zero. The mathematics these societies developed included things like negative numbers. So you start to get more sophisticated levels of mathematics.

So one of the earliest written text sub mathematics, that has Zero, negative numbers, even some sort of basic algebra, is written in South Asia in the early 7th century. This text makes its way into the Middle East, to Baghdad. And it’s eventually translated into Arabic by a Persian astronomer and mathematician. Once he began his translation, he quickly realizes the advantage of this system, the types of math that can be done. Soon, the text begins to be more widely circulated through the Middle East. And other mathematicians start to advocate using this number system.

So by the 10th century, it’s the dominant system in the Middle East. And as a consequence, algebra and other more sophisticated forms of mathematics start to flourish. Meanwhile, in Western Europe, the Roman Numeral System, a system without Zero, was still in place.

In the late 12th century, an Italian Mathematician named Fibonacci was travelling in North Africa along with his father, a merchant. And while he’s there, Fibonacci discovers this Arabic text. He translates the text into Latin, and returns to Europe. And he promotes the adoption of this number system because of the advantages in recording commercial transactions, calculating interests, things of that nature. Within the next century and the half, that becomes the accepted dominant number system in Western Europe.

Any questions? Robert?

Robert:Um, this Fibonacci, is he the same guy who invented that……um…….that series of numbers?

Professor:Ah……yes. The famous Fibonacci sequence. Although he didn’t actually invent it, it was just an example that had been used in your original text. I mean, can you imagine? Introducing the concept of Zero to Western Europe? And this is what you go down in history for?

Carol?

Carol:So, do we see like an actual change in everyday life in Europe after the Zero comes in? Or they really just……

Professor:Well, well, the change takes place is in the development of sciences.

Carol:Oh.

Professor:Even in basic engineering. It isn’t a radical change. Um, but as you start to get into, again, the theoretical sciences, ah, higher forms of mathematics, calculus, Zero had a much bigger influence in their development.Ok, now note that as cultural diffusion goes, this was a relatively slow instance. Some things tend to spread much quicker, um, for example, artistic, or architectural styles, such as domes used in architecture. We see evidence of that being diffused relatively quickly from Rome to the Middle East to South Asia……

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TPO51 纽约之旅

Trip To The New York City

Listen to a conversation between a student and the director of the Student Activity Center.

Director:Hello, Jack. Is everything set for the trip this Saturday?

Student:Everything’s ready. Ah, fifteen people have signed up. Our train gets into New York City at noon which leaves plenty of time to get downtown to the art gallery for the reception.

Director:It’s great. You could organize this. What an honor having a painting by one of our students in that exhibit!

Student:Yeah. My roommate’s so modest. If we weren’t such good friends, I’d never realize that his work was being exhibited. So, since I was going anyway for the opening and all, I figure that might as well make a student event out of it. Working here at the Student Activity Centers made me realize how popular our activities are. I figure they’ll be interested in it.

Director:Well you've done a super job organizing everything. This poster was great.And they were up in no time.

Student:Thanks. And I’m glad you could approve the funding for us.

Director:My pleasure. By the way, how are you getting to the gallery from the train’s station?

Student:Well, there are buses that run downtown.

Director:Right. You grew up in New York City, didn’t you?

Student:Yeah. But, the bus, well, that’s kind of what I want to talk to you about.

Director:Yes.

Student:I realized that at the last minute, but, well, the weather for Saturday is supposed to be really nice, sunny, warm. It’ll be a great opportunity to walk the High Line.

Director:The……what?

Student:Haven’t you?......Oh, I guess not everyone has heard of it. It’s this amazing……it’s like this park in the sky.

Director:A park in the sky?

Student:Yeah. Well, see there was this old train line. You know one of those elevated lines, the kind that run high above the streets?

Director:OK.

Student:Well, this one was used for freight, not passengers.

Director:Aha.

Student:But when it got cheaper to move freight by trucks, they stop using it. It was abandoned for a long time. And then, a few years back, the city agreed to turn the tracks and the surrounding area into a park. It’s not very wide but it’s over a mile long. And it goes from the train station all the way downtown near the gallery.I’ve walked before, it’s really cool.There was grass and flowers everywhere, and since you’re high up, you get these great views of the city.

Director:Sounds wonderful. But have you considered not everybody might be interested in walking that far? They might prefer the bus.

Student:Couldn’t we just split up?You know how some of us walk and the others take the bus?

Director:But remember, Jack, the poster advertises you as the tour leader, not everybody sees the adventure about getting around the city.You need to find someone to accompany people on the bus, then you take the walkers.

Student:Yeah. But who? Um, the trip’s in two days.

Director:Well, I did my graduate work in New York, of course it was a while ago, but I still know how to get around the city.

Student:Yeah……

Director:And I’d love to see that exhibit.

Student:You’d go? Ah, that’ll be great!

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TPO51 插画家奥德邦

Audubon The Famous Illustrator

Listen to part of a lecture in an art history class. The professor has been discussing illustrated books.

Professor:I want to take a look one particular book to give you an idea about what was involved in publishing illustrated books in the 1800s.The book’s called The Birds of the America and the illustrator was John James Audubon.

So,The Birds of the America, four volumes which contained illustrations of nearly every bird in the United States, over 400 birds, all hand-colored, all painted life-sized, the largest birds painted on the largest printing paper available at that time.This required a lot of dedication. And Audubon is best remembered as an incredibly meticulous accurate artist, a very accomplished illustrator of the natural world.

And while there were other artists working on the similar project at the same time, Audubon’s book remains the most well-known and successful of its kind. But, let’s talk a bit about Audubon himself first.

First of all, Audubon was not a traditional painter.And by this I mean that he didn’t work in oils. He preferred to use water color and pastel crayons.And he worked on paper instead of on canvas.The thing is, Audubon considered the illustrations in his book, not the original water colors, to be his finished product.His water colors were merely preparatory studies, most of which were painted while he was observing birds in the wild. These water colors were then sent to his printer who created the final prints for the book. And Audubon was so concerned with accuracy that he often scribbled notes to the printer around the edges of these original water colors.

In fact, you might question whether producing a work of art was even Audubon’s goal. Now, when I look at Audubon’s illustrations, I see a work of art. But, it may make more sense to consider Audubon, first and foremost, as a naturalist, as a scientist. See, the early 19th century when Audubon was painting was a time of major scientific inquiry. And an essential way of spreading scientific knowledge was through those illustrated books.

Student:So what did Audubon consider himself? An artist or a scientist?

Professor:I’m not sure the distinction between the two was all that clear in the 1800s. I think we can accurately state that the driving force in his art was getting the science right. And this was perhaps a point that critics of his art work at that time just didn’t appreciate.

Audubon also study birds in ways that didn’t directly inform his art. Ah, you know what bird banding is right? A bird has a band attached to its foot so we can learn about things like migration patterns. Well, the first recorded instance of anyone doing that, it was Audubon. Another example, a common belief of that time was that vultures used their sense of smell to find food. Audubon didn’t believe that. So, he tested it. He put a large painting of a dead sheep in a field, and sure enough, vultures found it and started pecking at it.

Now, Audubon’s work was very accurate, and we know this because we can compare his illustrations to the birds around us. But sometimes it’s not possible to check. There are actually several birds in his book that no one’s ever seen. These are sometimes called Audubon’s mystery birds, because even though he drew them, there is no evidence that they exist in the wild.

For someone who’s respected as a naturalist, isn’t it strange to think that he drew some birds that don’t appear to be real? For example, there is an illustration that appears to be a type of warbler, a small bird. It has a white ring around its eyes and white bars on its wings. No one’s ever seen a warbler like this, so some people wonder if Audubon maybe forgot certain details about this bird when he painted it, or that he copied another artist’s work. But considering that Audubon was such a meticulous artist, well, that might be a better answer.

Hybridization is something that’s well-known in birds. And it definitely explains the rather unique-looking duck Audubon painted. He himself suggested that maybe it wasn’t an unknown species but a hybrid, born from two different species. Since then, this particular crossing species has actually been recorded, both in the wild and in captivity. So it turns out that Audubon was right. And this duck actually was a hybrid.

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TPO51 日心说

Heliocentric Theory

Listen to part of a discussion in a history of science class. The class is discussing the heliocentric theory.

Male Student:What I found really difficult to understand is why the heliocentric theory, um, why wasn’t like believed by everybody right away?

Professor:Well, one thing that’s hard to do is to sort of see things from the perspective of someone who’s hearing that theory for the first time. I mean today we tend to assume that the moment the heliocentric theory was laid out, the idea that the Sun, not the Earth, was the center of the solar system, that you know, you’d have to be in denial, not to accept it. But it really wasn’t that easy.

Male Student:But the idea that the earth wasn’t the center of the universe……that has been tossed around for like centuries, right? I mean, lots of people would have the idea.

Professor:Yes, that’s true, going all the way back to the Ancient Greeks. But in Europe, when Galileo championed it in the 17th century, during part of his discoveries using a telescope, there still was some major resistance to it.

Male Student:But I still don’t understand why, I mean, isn’t it obvious?

Professor:Well, despite Galileo’s ingenious arguments in support of the heliocentric theory, there was still a lot of reasons why people of that period couldn’t buy into it. Remember, we are talking about four hundred years ago, so ah, let’s think about a few of those reasons, Ok?

So, first of all, they could work out that if the Earth was going around the Sun, then it had to be traveling at many thousands of kilometers per hour. And that was just beyond anything anyone could understand. You know, they could understand riding a horse or walking, maybe they could get up to 30, 32 kilometers per hour. But tens of thousands of kilometers per hour? That was just crazy. So, to many people, whatever is going on, it couldn’t be that.

Female Student:Um… So people didn’t believe the heliocentric theory because it was so hard to believe?

Professor:Exactly. But, there were more scientific kinds of reactions as well. Because, look, if you have ever been on a carousel or you are on a ride at an amusement park and you are on something that is going round round and round, two things, alright?One, you know you are moving, there is no doubt.And the other thing is, you know that unless you hold on tight, you are gonna go flying out because of centrifugal force, right?

Female Student:So, if I understand you for the average person 400 hundred years ago there was no evidence that we are moving at higher speed, right?Since everything was securely on the ground and no one was flying off into space?

Professor:Yes. And in particular. And this was one specific difficulty for people in the period, even if they thought that there was some sort of force that maybe kept you and me and buildings and things on the surface of the Earth. Their theory about the nature of the atmosphere was that nothing was holding it down. So if, if you can understand that way of thinking, then clearly, if the Earth, was moving at a great speed, we should’ve lost all our atmosphere a long time ago. You know, it would be like, trailing away behind us. And so, I want to try a little sort of experiment, because, I, I think that what we will find is that some of us have ideas about motion that actually fit with anti-heliocentrism.

Male Student:Anti-heliocentrism? No way. It’s the 21st century.

Professor:Well, then let’s see. So, picture the following. You are at the equator, moving at 1600 kilometers per hour. Ok? And you drop something, small and light, like a matchstick for example. Where is it going to land?

Male Student:That’s easy. It will be long gone. The matchstick is so light that it will fly right out of my hand and end up away behind me somewhere.

Professor:Ah, actually, that matchstick you dropped, it’ll land right at your feet.

Male Student:What?

Professor:Well, let’s think about it. If I got to consider that the Earth’s rotating at 1600 kilometer per hour at the equator, and you, me, the air, and that matchstick will all moving together at the same speed, even though it doesn’t seem or look or feel like we are moving. So class, clearly, even today, we actually have some inclination to think that if the Earth were moving around at a great speed, we all would see signs of it. Perhaps now you are less inclined to dismiss those who once found heliocentrism so hard to believe. Ok, let’s move on.

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