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4.1 Introduction

Domestication of dogs and of most other livestock took place so long ago that reconstructing the course of events is extremely difficult. Written records and illustrations describing the origins of many modern breeds are also sparse until the 19th century. We can only guess at what the domesticators were aiming to produce and how and when domesticated traits appeared in the species subjected to artificial selection. However, a little-known experiment on the domestication of red foxes (Vulp
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3.2 Angular size, actual size and distance

The angular size of an object is determined uniquely by its actual size and its distance from the observer. For an object of fixed size, the larger the distance, the smaller the angular size. For objects at a fixed distance, the larger the actual size of an object, the larger its angular size. For objects with small angular sizes, such as typical astronomical objects, the precise relationship between angular size, actual size and distance is well approximated by th
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1.3 Beyond visible light

During the twentieth century, astronomers extended their capabilities by developing telescopes and detectors that were sensitive to radio waves, microwaves, infrared and ultraviolet radiation, X-rays and gamma rays. All these forms of electromagnetic radiation, along with visible light, are emitted by the Sun.

Figure 6</span><br><span class=Author(s): The Open University

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6 Reflection

Most of the activities that you have done so far are based on your understanding of single sections that you have just read. Activity 8 which follows, is different. It requires you to assemble and integrate information over the whole ‘Life in the trees’ topic and is likely to require some extra effort and thought. Integrating information from different sections of the unit; is an important element in building your study skills. You're asked here to assemble evidence in support of a partic
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5.1 Introduction

The island of Madagascar is relatively small compared to the enormous landmasses of Africa, Asia and South America inhabited by the primates I've mentioned up to now. Yet of the 250 or so living primate species, more than 30 species of lemur live in Madagascar – an astonishingly high 13 per cent or so of all primate species. Their diversity is reflected in the identification of no fewer than five families, related in the way suggested in Author(s): The Open University

2.3 The colugo

In LoM, DA vividly describes one particular evolutionary development associated with tree dwelling – taking to the air [pp. 221–227]. The gliding habit evolved independently in different mammalian lineages and yet the anatomical modifications that allow it are similar in, for example, flying squirrels and the unrelated colugo. In particular, the ‘sail of skin’ [p. 221], technically termed a patagium, stretches between the limbs – and a good deal further in the colugo, acting as an e
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7 The threat of extinction

DA ends his book by writing eloquently of the dangers of extinction faced by mammals, from habitat loss as we exploit our environment to produce more and more food, for our growing population. However bleak the picture, there is still time and opportunity to save mammal species from extinction. Although bison in the USA and Canada were reduced to barely 1000 individuals in 1900, their numbers have now risen to well over 150 000 thanks to the efforts of First Nation indigenous peoples, and ran
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2.2 Energy flow in ecosystems

You are about to meet some very large numbers, expressed in scientific notation, and some new units. The new units are those that are used to measure the amount of solar energy received by a part of the Earth's surface. Since plants are dependent on light for photosynthesis, the amount of plant material that ca
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10 Living in herds

Wildebeest are only one of the species of plant predator that live in herds. Many others do too.

Activity 7

Watch the the TV programme from 30.48–47.32 and read LoM p. 109. Identify and write down (a) a couple of advantages and
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5.1 Monogamy and polygamy

You've seen plenty of evidence that reproduction in rodents – more precisely what I've called their reproductive strategies – are versatile and varied. You'll appreciate that ‘versatile and varied’ describes the range of sexual habits seen in the rodents as a group, not the behaviour within a single species. As DA says, some are monogamous, which means that individuals mate exclusively with one partner, over at least a single breeding cycle or season. The marmots are an example of a g
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4.1 A measure of success

If what I have highlighted so far were the whole story, the only adaptive features shown would be those that equipped the rodent for times of famine, which is patently not the case. It is obviously a very important factor in the production of new species because the most productive of rodents (rats and mice) account for about 1300 of the 2000 or so rodent species, following the figures given in the TV programme. In LoM you have seen many interesting characteristics to which adaptive functions
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6.2.2 The Earth's motion relative to the 3 K radiation

Radiation has energy and momentum, so we can use the molecules of a fluid such as air as an analogy for the photons of radiation. A detector pointing forwards along the direction of our motion (if any) will encounter a greater number of photons than a detector pointing backwards; in other words, it will record a higher intensity of 3 K radiation. (If the detector is tuned to a narrow band of frequencies one would also have to take account of the change in observed spectrum, but the principle
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3.2 Some general properties of galaxies

Firstly, we note that galaxies tend to occur in clusters rather than singly. The mutual gravitational attraction of galaxies naturally tends to hold them on paths that remain close to each other. Typically a cluster contains tens or hundreds of galaxies. There are, however, large clusters with thousands of galaxies, and there are some solitary galaxies. Our own Galaxy is a member of a smallish cluster of about 36 galaxies called the Local Group (see Author(s): The Open University

5.2 The energy of electromagnetic waves

The energy density of an electric field E is

Although we will not prove it in this unit, a very similar result applies to magnetic fields. The energy density of a magnetic field B is

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5.1.2 Getting agreement with Gauss's law

Substituting the assumed form of the electric field (Equation 7.20) into the empty-space version of Gauss's law (Equation 7.16) gives

The first two partial derivatives are equal to zero because f does not depend on x or y. So we obtain


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4.2 DDT: a classic case in ecotoxicology

DDT is very effective in controlling pests, being very toxic to insects, and is cheap to produce. Its effectiveness is enhanced because it is very persistent, remaining active in the environment for a long time. This increases its value as an insecticide to farmers because one application lasts a long time, but is also a major reason why it poses a threat to wildlife and to human health. Although the agricultural use of DDT was banned in most developed countries 30 years ago, it can still be
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Acknowledgements

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Grateful acknowledgement is made to the following sources for permission:

Illustrat
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3.1 Graphs

Information is everywhere these days – in the form of images, written records, tables and graphs. In this part of the unit we want you to realise how useful graphs can be to analyse numerical information, and to show you some techniques that can help you decide how reliable this numerical information is.

It's often difficult to spot a trend or a relationship in a long list of numbers. Because the human mind is highly adapted to recognising visual patterns, it is often much easier to u
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1.4.1 Study Note 2

An important point to remember when writing down measurements from a scale is never to quote more decimal places than you can reliably read from the measuring device you are using.

Figure 4
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6 Unit summary

  • A discrete exotic terrane refers to a large crustal fragment that can be recognised by its distinct sedimentary, igneous, metamorphic and structural history compared with that of its eventual neighbours, and has been juxtaposed into position by major strike–slip faults.

  • Nine discrete exotic terranes make up the Basement in the British Isles. These consist primarily of Precambrian metamorphosed rocks but also contain some unmetamorphosed sedi
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