Chapter 22 Descent With Modification A Darwinian View of Life 1 Chapter 22 Descent With Modification A Darwinian View of Life o Endless Forms Most Beautiful Darwin published his hypothesis in The Origin of Species Evolution descent with modification a phrase used in proposing that Earth s many species are descendants of ancestral species that were different from the present day species Evolution can also be defined as a change in the genetic composition of a population from generation to generation Evolution can be viewed as a pattern or a process Pattern revealed by data from a range of scientific disciplines including biology geology physics and chemistry these data are facts observations about the natural world Process consists of the mechanisms that produce the observed pattern of change represent natural causes of the natural phenomena we observe Concept 22 1 The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species o Scala Naturae and Classification of Species Aristotle 384 322BCE viewed species as fixed unchanging He concluded that life forms could be arranged on a ladder or scale of increasing complexity later called Carol Linnaeus 1707 1778 a Swedish physician and botanist developed the two part or binomial format for naming Linnaeus adopted a nested classification system grouping similar species into increasingly general categories Darwin argued that classification should be based on evolutionary relationships o Scientists using the Linnaean system often grouped organisms in ways that reflected those scala naturae species relationships o Ideas About Change over Time Darwin drew from the work of scientists studying fossils the remains or traces of organisms from the past New layers of sediment cover older ones and compress them into superimposed layers of rock called strata Paleontology the study of fossils was developed by French scientist George Cuvier 1769 1832 Cuvier noted that the older the stratum the more dissimilar its fossils were to current life forms Cuvier opposed the idea of evolution He advocated catastrophism the principle that events in the past occurred suddenly and were caused by mechanisms different from those operating in the present Each boundary between strata represented a catastrophe such as a flood that had destroyed many of the species living at that time He proposed that these periodic catastrophes were usually confined to local regions which were later populated by different species immigrating from other areas In 1975 Scottish geologist James Hutton 1726 1797 proposed that Earth s geologic features could be explained by gradual mechanisms still operating today o o o o o o o o Chapter 22 Descent With Modification A Darwinian View of Life 2 He suggested that valleys were formed by rivers going through rocks The leading geologist of Darwin s time Charles Lyell 1797 1875 incorporated Hutton s thinking into his principle of uniformitarianism which stated that mechanisms of change are constant over time o Lamarck s Hypothesis of Evolution French biologist Jean Baptiste de Lamarck 1744 1829 proposed a mechanism for how life changes over time By comparing living species with fossil forms Lamarck had found what appeared to be several lines of descent each a chronological series of older to younger fossils leading to a living species Lamarck explained his findings using two principles use and disuse the idea that part s of the body that are used extensively become larger and stronger while those that are not used deteriorate o The second principle inheritance of acquired characteristics stated that an organism could pass these modifications to its offspring Concept 22 1 Summary The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging Darwin proposed that life s diversity arose from ancestral species through natural selection a departure from prevailing In contrast to catastrophism the principle that events in the past occurred suddenly by mechanisms not operating today Hutton and Lyell thought that geologic change results from mechanisms that operated in the past in the same manner as at the present time uniformitarianism Lamarck hypothesized that species evolve but the underlying mechanisms he proposed are not supported by evidence Concept 22 2 Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity species views o o o of life o Darwin s research Henslow a botany professor o The Voyage of the Beagle Charles Darwin 1809 1882 was born in Shrewsbury At Cambridge Darwin became the prot g of the Reverend John The primary mission of the voyage was to chart poorly known stretches of the South American coastline Darwin observed that the plants and animals in temperate regions of South America more closely resembled species living in the South American tropics than species living in temperate regions of Europe Darwin reinforced what he learned from Lyell Principles of Geology The physical evidence did not support the traditional view that Earth was only a few thousand years old Darwin collected different birds although the animals on the Galapagos resembled species living on the South American mainland most of the Galapagos species were not known from anywhere else in the world Darwin hypothesized that the Galapagos had been colonized by organisms that had strayed from South America and then diversified giving rise to new species on the various islands o Darwin s Focus on Adaptation environments Adaptations inherited characteristics of organisms that enhance their survival and reproduction in specific Chapter 22 Descent With Modification A Darwinian View of Life 3 Darwin began to perceive adaptation to the environment and the origin of new species as closely related processes Darwin s explanation of how adaptations arise centered on natural selection a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because In his book On the Origin of Species by Means of Natural Selection The Origin of Species Darwin explains three broad of those traits o The origin of species observations The unity of life The diversity of life The match between organisms and their environments o Descent with Modification Organisms share many characteristics leading Darwin to perceive unity in life He attributed the unity of life to the descent of all organisms from an