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Chapter 17

BI111 Chapter 17

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Tristan Long

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Chapter 17 Darwin, Fossils and Developmental Biology 17.1 Recognition of evolutionary change • Buffon was confused as to why animals had useless body parts (pigs have two toes on each foot that never touch the ground) so he proposed that animals must have changed since their creation. • Vestigial structures: useless body parts • Suggested vestigial structures must have functioned in ancestral organisms • Cuvier developed theory of catastrophism: reasoning that each layer of fossils represented the remains of organisms that had died in a local catastrophe such as a flood • Lamarck proposed that a metaphysical “perfecting principle” caused organisms to become better suited to their environments. Simple organisms evolved into more complex ones moving up the ladder of life • Lamarck theorized two mechanisms fostered evolutionary change 1. Principle of use and disuse: body parts grow in proportion to how much they are used 2. inheritance of acquired characteristics: changes that an animal acquire during its lifetime are inherited by its offspring • Despite shortcomings of his theories he still made 4 important contributions 1. he proposed that all species change through time 2. he recognized that changes are passed from one generation to the next 3. he suggested that organisms change in response to their environments 4. he hypothesized the existence of specific mechanisms that caused evolutionary change 17.2 Changes in Earth • Hutton’s gradualism, the view that the Earth changed slowly over its history, contrasted sharply with Cuviers catastrophism 17.3 Charles Darwin • On the Galapagos Islands he found strange and wonderful creatures including giant tortoises and lizards that dived into the sea to eat algae • Darwin hypothesized that the plants and animals of the Galapagos were descended from South American ancestors and that each species had changed after being isolated on a particular island • By selectively breeding individuals with favourable characteristics, breeders enhanced these traits in future generations: artificial selection • Species typically produce many more offspring than are needed to replace the parent generation Darwin’s Observations and Inferences about Evolution by Means of Natural Selection Observations Inferences Most organuisms produce more than one or two Individuals within a offspring population compete for A populations Populations do not increase limited resources characteristics will change in size indefinetly over the generations as Individuals with advantageous, heritable populations exhibit Hereditary characteristics characteristics become more common variability in many may allow some individuals characteristics to survive longer and Many variations have a reproduce more than others genetic basis that is inherited by subsequent generations • Darwin argued that all the organisms that have ever lived arose through descent with modification, the evolutionary alteration and diversification of ancestral species • On the Origin of Species was an explanation of how natural selection acted on the variability within groups of organisms, preserving favourable traits and eliminating unfavourable ones 17.4 Evidence for evolution: the fossil record • Palaeontologists discover, describe and name species of fossils • Fossils usually preserve the details of hard structures: bones, teeth, shells of animal or wood, leaves, and pollen of plants • Fossils rarely form in habitats where sediments do not accumulate (mountain forests) or where soils are acidic (forests) 17.5 Earth history, biogeography and convergent evolution • Theory of plate tectonics: Earth’s crust is broken into irregularly shaped plates of rock that float on its semisolid mantle • Continental drift: currents in the mantle cause the plates and continents in them to move • Panega was the fist land mass that got separated into today’s continents • Drifting continents induced global changes in Earth’s climate, encouraged formation of glaciers and dropped Earth’s temperature • Many species have continuous distribution: living in suitable habitats throughout large areas • Disjunct distributions: species live in widely separated locations • Dispersal: the movement of organisms away from their place of origin, it can produce a disjunct distribution if a new population becomes established on the far side of a geographic barrier • Vicariance: the fragmentation of a continuous geographic distribution by external factors • Edemic species: a species that occurs in that place and nowhere else on Earth (Aus
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