Theory of Evolution Chapter 13 The History of Evolutionary Thought Evolution The development of new types of organisms from preexisting types of organisms over time. Also could be described as a heritable change in characteristics within a population from one generation to the next The primary mechanism of evolutionary change producing adaptation of organisms to their environment is natural selection, the differential survival and reproduction of individuals within a population The History of Evolutionary Thought Darwin’s Ideas Used the phrase “descent with modification” to describe the process of evolution Every species, living or extinct, must have descended by reproduction from preexisting species and that species must be able to change over time. Theory of Natural Selection (Darwin) 1. Overproduction More offspring are produced than can survive to maturity Theory of Natural Selection (Darwin) 2. Genetic Variation Within a population, individuals have different traits. Ex: Thick fur Occasionally, new traits may appear in a population Theory of Natural Selection (Darwin) 3. Struggle to Survive Individuals must compete with each other Some variations improve an individuals chances to reproduce, but some variations reduce this chance. Theory of Natural Selection (Darwin) 4. Differential Reproduction Organisms with the best adaptations are likely to survive and reproduce Through inheritance, the adaptations will become more frequent in the population Darwin proposed natural selection as the mechanism of evolution Note these important points – – – Individuals do not evolve: populations evolve Natural selection can amplify or diminish only heritable traits; acquired characteristics cannot be passed on to offspring Evolution is not goal directed and does not lead to perfection; favorable traits vary as environments change Copyright © 2009 Pearson Education, Inc. EVIDENCE OF EVOLUTION Artificial Selection this process occurs when a human breeder chooses individuals that will parent the next generation. Fossil Evidence The fossil record shows that organisms have evolved in a historical sequence – – – The oldest known fossils are prokaryote cells The oldest eukaryotic fossils are a billion years younger Multicellular fossils are even more recent Copyright © 2009 Pearson Education, Inc. Fossils Fossil – the remains or traces of an organism that died long ago. Show that different types of organisms appeared at different times and places on earth. Superposition – this principle states that if the rock strata at a location have not been disturbed, the lowest stratum was formed before the strata above it. Geologists put together a timeline for the order in which different groups of rocks and fossils were formed. The Geologic Time Scale Relative age – its age compared to that of other fossils. Absolute age – more accurate using radiometric dating Not all fossils are discovered and not all remains become fossilized Distribution of Fossils Different organisms lived at different times Today’s organisms are different from those of the past Fossils found in adjacent layers are more like each other than fossils found in deeper or higher layers. 4. By comparing fossils and rocks from around the planet, we can infer when and where different organisms existed. 5. Species have differed in a gradual sequence of forms over time. 1. 2. 3. Biogeography Biogeography, the geographic distribution of species, suggested to Darwin that organisms evolve from common ancestors – Darwin noted that animals on islands resemble species on nearby mainland more closely than they resemble animals on similar islands close to other continents Copyright © 2009 Pearson Education, Inc. Transitional Species Have features that are intermediate between those of hypothesized ancestors and later descendant species. Pakicetus (terrestrial) Rhodocetus (predominantly aquatic) Pelvis and Dorudon (fully aquatic) hind limb Pelvis and hind limb Balaena (recent whale ancestor) Anatomy and Embryology Homologous structures – anatomical structures that occur in different species and that originated by heredity from a structure in the most recent common ancestor of the species. Anatomy and Embryology Analogous structures have closely related functions but do not derive from the same ancestral structure. Anatomy and Embryology Vestigial structures – seem to serve no function but that resemble structures with functional roles in related organisms. Anatomy and Embryology The development of animal embryos is also evidence of descent with modification Pharyngeal pouches Post-anal tail Chick embryo Human embryo Biological Molecules Biologists can compare the DNA, RNA, proteins, and other biological molecules from many different organisms. They can then look for similarities and differences among the data for each species The greater the number of similarities between any given species, the more closely the species are related through a common ancestor.