5 Summary Domesticated organisms evolve in artificial environments under artificial selection, and opportunistic or enforced hybridisation often occurs between species that would not normally interbreed. Natural selection cannot be eliminated and continues to operate. At least two different forms of dwarfism are common in domesticated livestock and humans, but only the rarer midget type of dwarfism occurs in wild lineages. Domesticated mammals and birds have distinctive patterns of skin pigmentation th
3.1 The origins of domesticated dogs Archaeologists and biologists agree that dogs (Canis familiaris) were the first species to become domesticated. Francis Galton, Darwin's younger cousin, suggested at the end of the 19th century that domestication began when humans captured and raised wolf puppies. The resulting adults ate scraps of human food, assisted in hunting and acted as guard dogs around camps. Among the evidence in support of this hypothesis is the observation that tribal people all over the world take wild anim
2.3 Skin pigmentation and pattern Most domesticated livestock differ from their wild ancestors in the colour and pattern of the skin, hair or feathers. What gene-associated Learning outcomes When you have completed this unit you should be able to: define the terms ‘artificial selection’ and ‘domestication’ and explain the relationship between artificial and natural selection; describe some forms of dwarfism in modern breeds of dogs and explain their relationship to dwarfism in humans and in modern and extinct wild mammals; describe some features of the skin, fur, feathers and the shape of the head frequently observed in domestic 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 3 Measuring the Sun Section 2 referred to observations that can only be made using sophisticated telescopes, but this section turns to an observation you can do yourself. There are two reasons for this: one is to give you experience in scientific measuring and the other is to introduce some terminology that astronomers use frequently. 1.1 The Sun at visible wavelengths The Sun is seen as a blindingly bright, yellow object in the sky. The part of the Sun that you normally see is called the photosphere (meaning ‘sphere of light’); this is best thought of as the ‘surface’ of the Sun, although it is very different from the surface of a planet such as Earth. Its diameter is about 1.4 million kilometres, making the Sun's volume roughly one million times that of the Earth. The photosphere is not solid. Rather, it is a thin layer of hot gaseous mater 1 Observing the Sun
Never look directly at the Sun, either with the unaided eye or through spectacles, binoculars or a telescope. You risk permanently damaging your eyes if you do so. Learning outcomes At the end of this unit you should: know about the electromagnetic spectrum and how it is used to infer properties of sources of radiation; know about the range of sizes, distances and motions of objects in the Universe and how they can be measured; know about the structure of, and the main processes operating in, the Sun; comprehend concepts lying well outside everyday experience, including those that involve very large and very smal Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: The content acknowledged below is Proprietary and is used under licence. 5.3.4 Aye-ayes Perhaps with good reason, the aye-aye has been dubbed by some ‘the strangest of all primates’ and LoM provides some of the reasons [p. 243]. Little wonder that, as DA points out, the species was first classified as a rodent like them, it has powerful incisor teeth that grow continuously. 5.5.2 Indris and sifakas Both indris and sifakas are unusual amongst lemurs in that they are active largely by day. Leaves are their primary food. They have a specialised form of locomotion, best described as ‘vertical clinging and leaping’ and the leaps they can take, using their powerful legs, can be up to 10 m. DA describes the bounding movement of sifakas when they are compelled to come to ground. (If you go back to the previous video sequence that shows this strikingly white species – the so-called silky s 5.2 Madagascan diversity Watch the video sequence below, which focuses on just three lemur species – the ring-tailed (in a very brief sequence, leaping from one tree to another), the golden bamboo lemur, already mentioned, and the sifaka, plus the 4 Galagos, lorises and pottos Activity 6 is divided into several parts, on successive pages, and asks you to answer a number of questions. Look ahead to this activity now and highlight, or list, the different ‘process’ words, which tell you what you need to do with the content You should have found ‘describe’, ‘contrast’, ‘eva 8 What makes a successful omnivore? From what has been said already, there's good evidence that the key physical characteristic of the great majority of omnivores is a non-specialist dentition. What about other aspects of their biology? Question: Many omni 3 Is specialisation always advantageous? Specialisation generally implies the possession of adaptations that make animals particularly effective or efficient in one or more aspects of their lives. In many of the examples used in other units in this series, mammals are likely to possess adaptations related to the acquisition and/or processing of food. 10 Living in herds Wildebeest are only one of the species of plant predator that live in herds. Many others do too. 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 6.2.4 The speed and direction of the Earth's motion The first significant claim to have detected the motion of the Earth relative to the ‘frame of isotropic 3 K radiation’ came in 1977 from a group at Berkeley, California. They concluded that the Earth is moving at a speed of (390 ± 60) km s−1, in a direction towards the constellation Leo, relative to a frame in which the 3 K radiation is isotropic. Their conclusion resulted from observations of a variation of intensity with angle of the form predicted by Equation 14, which w 5.3 The redshift of the 3 K radiation The temperature, T, of the radiation is proportional to the most probable photon energy, E, which as we have said is proportional to f, and hence inversely proportional to the wavelength λ. Thus, According to Equation 1, we have for the redshift, z 3.3 Extending the distance scale Having reviewed some of the properties of galaxies, we are now in a position to return to the question of how we are to develop further our methods of measuring distance. The various steps taken in determining larger distances from known smaller ones are often called ‘rungs in the distance ladder’. The process of constructing a rung has been: Find a measurable quantity associated with a class of objects. Observe how the measura
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