4.2 Developing a Theory to Explain Change

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1 4.2 Developing a Theory to Explain Change In this section, you will: Compare different explanations for changes in populations over time Describe evidence to support the theory of evolution Explain how scientific knowledge is accumulated and organized to develop theories Analyze data to determine relatedness among organisms Developing a Theory to Explain Change How did life develop on Earth? Theories developed through observations, analysis of data and the formulation of hypotheses. Theory of Evolution by Natural Selection Contributors: Greeks Plato and Aristotle believed life was perfect. Georges-Louis Leclerc- noted similarities between humans and apes Georges Cuvier developed paleontology and noted strata of fossils with species appearing and disappearing. Idea of revolutions natural disasters killing species. Georges-Louis Leclerc, Comte de Buffon One of the first people to challenge the idea that life forms do not change 1

2 Georges Cuvier Largely credited with developing the science of paleontology Theory of Evolution by Natural Selection Charles Lyell disagreed with Cuvier and believed change was slow Jean-Baptiste Lamarck believed species increased in complexity over time and believed in acquired characteristics being able to be passed on from one generation to the next = inheritance of acquired characteristics (ex. Giraffe neck) Charles Lyell Suggested, unlike Cuvier, that the geological processes take long periods of time Earth is aged Jean-Baptiste Lamarck Developed an early idea regarding how animals change over time- inheritance 2

3 Theory of Evolution by Natural Selection Continued Charles Darwin companion on H.M.S Beagle & Alfred Wallace Populations change over time Competition for limited resources selects for the fittest All life starts with an unknown organism On the Origin of the Species Charles Darwin Traveled aboard on the HMS Beagle Surveyed coast of South America Observations regarding organisms Darwin s On the Origin of Species Book proposed two main ideas: 1. Present forms of life have descended from ancestral species 2. The mechanism for modification is natural selection that takes place over a long period of time Further Evidence for Evolution Since publishing of On the Origin of Species evidence has been collected to support theories Biologists, geologists, geographers, and paleontologists have all contributed evidence supporting evolution 3

4 Alfred Russel Wallace Wallace studied organisms in South America and Malaysia Fossil Record Young layers species are similar to species today. Appear in chronological order. Chronological- passage of time (date) Transitional fossils - remains that exhibit traits common to both an ancestral group and its derived descendant group Over time, transitional fossils are found that fill the gaps and link different species together Patterns of Distribution Geographically close locations have similar fossils. Fossil Record Fossils Fossils are formed within sedimentary rock The layer in which a fossil is found often is indicative of the age of that particular specimen Patterns of Distribution Biogeography- study of the past and present geographical distribution of organisms Many of the observations used by Wallace and Darwin were based on biogeography 4

5 Anatomy Homologous structures similar structure but different function (bat wing and human hand) Analogous structures- perform similar functions, even though the organisms do not have a common evolutionary origin. Ex. Bat and insect wing (same function different ancestor) Homologous Structures and Evolution Homologous structures point to a common ancestor Variations in the structure over time made the homologous structures useful adaptations for different environments Analogous structures (those with a similar function, but different origins) do not lend evidence to evolution Embryology Embryos of various organisms exhibit similar stages of development All have paired pouches in throat (gills, ears, throat) 5

6 Most vertebrate embryos are similar to each other at some point in their development Points to common ancestral origin Embryology Molecular Biology All cells have cell membranes Enzymes Proteins from amino acids DNA Genetics Today used to link species and support the theory of evolution. 6

7 Genetics When Darwin proposed his theory of evolution, very little was understood regarding genetics We now know the following: 1. Species pass on their traits to offspring using genetic material 2. The genetic material can randomly change (mutations), leading to variation in traits 7