TPO 16 Script Lecture 3
Narrator:
Listen to a part of a lecture in a biology class.
Professor
OK. Let's continue our discussion about animal behavior by talking about decisions that animals face, complex ones. Animals, even insects, carry out what look like very complex decision making processes. The question is how. I mean no one really thinks that, say a bee goes through weighing the pros and cons of pollinating this flower or that flower. But then how do animals solve complex questions, questions that seem to require decision making. The answer we'll propose of course is that their behavior is largely a matter of natural selection. As an example, let's look at foraging behavior among beavers.
Beavers eat plants, mostly trees. And they also use trees and tree branches to construct their homes in streams and lakes. So when they do forage for food and for shelter materials, they have to leave their homes and go up on land where their main predators are. So there are a number of choices that have to be made about foraging. So for example, um... they need to decide what kind of tree they should cut down. Some trees have higher nutritional value than others, and some are better for building material, and some are good for both... um...aspen trees. Beavers peel off the bark to eat and they also use the branches for building their shelters. So aspens do double duty. But ash trees, beavers use ash trees only for construction. Another decision is when to forage for food. Should they go out during the daytime when it's hotter outside and they have to expend more energy, or at night when the weather is cooler but predators are more active? Ok, but there are two more important issues, really the most central, the most important, OK? First, let's say a beaver could get the same amount of wood from a single large tree when it has lots of branches as it could get from three small trees. Which should it choose? If it chooses one large tree, it' have to carry that large piece of wood back home, and lugging a big piece of wood 40 or 50 yards is hard work, takes a lot of energy. Of course it'll have to make only one trip to get the wood back to the water On the other hand, if it goes for three small trees instead, it will take less energy per tree to get the wood back home but it'll have to make three trips back and forth for the three trees. And presumably, the more often it wanders from home, the more it's likely to be exposed to predators. So which is better, a single large tree or three small trees? Another critical issue and it's related to the first, to the size issue, is how far from the water should it go to get trees. Should it be willing to travel a greater distance for a large tree, since it'll get so much wood from it? Beavers certainly go farther from the water to get an aspen tree than for an ash tree. That reflects their relative values. But what about size? Will it travel farther For a larger tree than It will for a smaller tree? Now I would have thought the bigger the tree, the farther the beaver would be willing to travel for it. That would make sense, right? If you're going to travel far, make the trip worth it buy bringing back most wood possible.
But actually, the opposite is true. Beavers will cut down only large trees that are close to the water. They will travel far only to cut down certain small trees that they can cut down quickly and drag back home quickly. Generally, the farther they go from the water, the smaller the tree they will cut down. They're willing to make more trips to haul back less wood, which carries a greater risk of being exposed to predators. So it looks as though beavers are less interested in minimizing their exposure to predators and more interested in saving energy when foraging for wood, which may also explain why beavers forage primarily during the evenings.
OK, so why does their behavior indicate more of a concern with how much energy they expend than with being exposed to predators? No one believes a beaver consciously weighs the pros and cons of each of these elements. The answer that some give is that their behavior has evolved over time. It's been shaped by constraints over vast stretches of time, all of which comes down to the fact that the best foraging strategy for beavers isn't the one that yields the most food or wood. It's the one that results in the most descendants, the most offspring. So let's discuss how this idea works.
TPO 16 Script Lecture 4
Narrator: Listen to part of a lecture in an art history class.
Professor
OK, now urn, a sort of paradigmatic art form of the Middle Ages was stained glass art. Stained glass of course is simply glass that has been colored and cut into pieces and re-assembled to form a picture or a decorative design. To truly experience the beauty of this decorative glass you should see it with light passing through it, especially sunlight, which is why stained glass is usually used for windows. But of course it has other uses, especially nowadays. Urn, anyway the art of making stained glass windows developed in Europe, urn, during the Middle Ages and was closely related to church building. In the early 1100s a church building method was developed that reduced the stress on the walls so more space could be used for window openings allowing for large and quite elaborate window designs. Back then, the artists made their own glass, but first they came up with the design. Paper was scarce and expensive, so typically they drew the design onto a white tabletop. They'd draw the principal outline but also outline the shape of each piece of glass to be used and indicate its color. Now in the window itself the pieces of glass would be held together by strips of lead. So in the drawing the artists would also indicate the location of the lead strips. Then you could put a big piece of glass on the tabletop and see the design right through it and use it to guide the cutting of the glass into smaller pieces.
Student
And the lead that was just to hold the pieces of glass together?
Professor
Well, lead is strong and flexible so it's ideal for joining pieces of glasses cut in different shapes and sizes. But up to the 15th century the lead strips also helped create the design.They were worked into the window as part of the composition. They were used to outline figures to show boundaries just like you might use solid lines in a pencil drawing.
Student
How did they get the color'? I mean how did they color the glass?
Professor
Well up until the 16th century stained glass was colored during the glass making process itself. You got specific colors by adding metallic compounds to the other glass making ingredients. So if you wanted red you added copper if you wanted green you added iron. You just added these compounds to the other ingredients that the glass was made of.
Student
So each piece of glass is just one color?
Professor
Yes, at least up until the 16th century. Then they started... urn.. .you started to get painted glass. Painted glass windows are still referred to as stained glass but the colors were actually painted directly onto clear glass after the glass was made. So um with this kind of stained glass you could paint a piece of glass with more than one color.
Student
And with painted glass they still used the lead strips?
Professor
Yes, with really large windows it took more than one piece of glass, so you still needed lead strips to hold the pieces together. But the painters actually tried to hide them. So it was different from before when the lead strips were part of the design. And it is different, because with painted glass the idea of light corning through to create the magical effect wasn't the focus any more. The paintwork was. And painted glass windows became very popular In the 19th century, people started using them in private houses and public buildings. Unfortunately, many of the original stained glass windows were thought to be old fashioned and they were actually destroyed, replaced by painted glass.
Student
They actually broke them? That showed good judgment, real foresight, didn't it?
Professor
Yes, if only they had known. Uh, and it's not just that old stained glass is really valuable today, we lost possibly great artwork. But luckily there was a revival of the early techniques in the mid-I 800s and artists went back to creating colored glass and using the lead strips in their designs. The effects are much more beautiful. In the 19th century Louis Tiffany came up with methods to create beautiful effects without having to paint the glass. He layered pieces of glass and used thin copper strips instead of lead, which let him make these really intricate flowery designs for stained glass, which are used in lamp shades You've heard of Tiffany lamp shades right? These of course took advantage of the new innovation of electric lighting. Electric light bulbs don't give quite the same effect as sunlight streaming through stained glass but it's close. So layered glass, Tiffany glass, became very popular and still is today. So let's look at some examples of different types of stained glass from each era.
