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1 THE EVIDENCE FOR EVOLUTION “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” (C. Darwin, 1859) I. FOUR PREMISES OF DARWIN'S THEORY OF EVOLUTION Charles Darwin's theory of evolution by natural selection can be summarized by four premises, read in logical sequence: a) More individuals are produced than can survive – consequently b) There is a struggle for existence, and because c) Individuals vary in features that influence their survival and reproduction (no two individuals are exactly the same, and some will do better than others –i.e. natural selection), AND IF d) Those features that favor some individuals over others are heritable, there will be EVOLUTION That is, those varieties or features that do better will become more abundant in subsequent generations – and the species or population will have been observed to evolve. Evolution is often described as "descent with modification", referring to the fact that changes are passed on from one generation to the next. Although evolution is often described as a "theory", much of it is fact. That is, we can observe all four of the premises occurring in nature and in the lab, and we can document the fact that evolution occurs. What we cannot observe directly is the evolution that has gone on for millennia; as you will see, it is partially but not perfectly documented by the fossil record and in the DNA of all organisms. Today's lecture will discuss the primary evidence we have for evolution – some of it was recognized by Darwin and forms the major part of his treatise on the Origin of Species – but some of it will come from examples that have been discovered since his time. I will argue that there are 6 major lines of evidence in support of the theory of evolution by natural selection. They are: 1) DIRECT OBSERVATION 2) COMPARATIVE ANATOMY
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2 3) EMBRYOLOGY/DEVELOPMENT 4) BIOGEOGRAPHY 5) FOSSIL RECORD (PALEONTOLOGY) 6) CLASSIFICATION/ TAXONOMY In this lecture, we will focus on #1, direct observation, and briefly discuss each of the other five. Subsequent lectures will look at each of these in more detail. II. DIRECT OBSERVATION What do I mean by direct observation? It is the observation of the process of evolution or modification by descent as it occurs – and thus within human time scales (e.g. decades or less). We will examine three examples: a) industrial melanism (peppered moth) b) pesticide resistance (DDT) c) artificial selection Industrial Melanism . Industrial melanism refers to a darkening in the color of several insect species that co-occurred alongside increased industrial air pollution in the late 19th-early 20th century. The most famous example of this phenomenon is from Britain, and involves a species of moth known as Biston betularia or the Peppered Moth. It has speckled wings – and occurs in two forms : a dark or melanic form, and a lighter, speckled form.
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