Natural Selection as the Mechanism for Evolution Chapter 14, Section 3

Lyell’s Influence In attempt to explain the past in terms of present day processes, Darwin went to local farmers and animal breeders and observed… Variation in the organisms that could be inherited Variation in the organisms that could be inherited After many generations, organisms appear very different from ancestors After many generations, organisms appear very different from ancestors Darwin called this process ARTIFICIAL SELECTION

NATURAL SELECTION 1. Variation in Nature No two organisms are exactly alike! No two organisms are exactly alike! 2. Struggle for Existence (Malthus) High birth rates and limited resources will cause organisms to compete High birth rates and limited resources will cause organisms to compete Selective pressures (predation, competition, parasitism, disease, pesticides, etc) Selective pressures (predation, competition, parasitism, disease, pesticides, etc) 3. Survival of the Fittest Organisms with the best adaptations survive and reproduce more often Organisms with the best adaptations survive and reproduce more often 4. Reproduction of Viable Offspring Offspring must be fertile and reproduce Offspring must be fertile and reproduce

Evidence of Evolution Chapter 14, Section 2

The Fossil Record Fossils are buried in sedimentary rock → Relatively, deeper fossils are older Fossils are buried in sedimentary rock → Relatively, deeper fossils are older Fossils provide evidence of changing life Fossils provide evidence of changing life Paleontologists search the fossil record for ancestral life forms Paleontologists search the fossil record for ancestral life forms

Geographic Distribution The geographic distribution of animals serves as a clue to how modern species evolved The geographic distribution of animals serves as a clue to how modern species evolved Two islands in different parts of the world (with similar environments) will house species similar to the nearest mainland rather than the other island Two islands in different parts of the world (with similar environments) will house species similar to the nearest mainland rather than the other island Ex: Australia’s unique plants and animals evolved from isolation from other continents Ex: Australia’s unique plants and animals evolved from isolation from other continents

Similarities in Structure The forelimbs of all mammals are made of bones that are similar in origin (skeletal structure), but may vary in function → called homologous structures The forelimbs of all mammals are made of bones that are similar in origin (skeletal structure), but may vary in function → called homologous structures Vestigial structures are remnants of structures in an animal that may have had a function or purpose in ancestral species, but serve no apparent function or purpose in modern species Vestigial structures are remnants of structures in an animal that may have had a function or purpose in ancestral species, but serve no apparent function or purpose in modern species

Structures (cont.) Homologous Same bones, different function (ex:forelimbs) Same bones, different function (ex:forelimbs) Evidence of common ancestry Evidence of common ancestry Analogous Different bones, same function (ex:wings) Different bones, same function (ex:wings) Evolve in UNRELATED species due to similar niches (roles) or similar environments Evolve in UNRELATED species due to similar niches (roles) or similar environments

Similarities in Development Embryology: the study of embryo development Embryology: the study of embryo development Animals that are more closely related will have more similarities in the stage of development Animals that are more closely related will have more similarities in the stage of development

Molecular Biology In recent decades, biologists have been able to look at DNA and amino acid sequences of animals to determine relatedness In recent decades, biologists have been able to look at DNA and amino acid sequences of animals to determine relatedness The more differences, the more distantly related the species The more differences, the more distantly related the species Darwin did not have this molecular evidence to support his hypothesis when he published his idea Darwin did not have this molecular evidence to support his hypothesis when he published his idea