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Evolution and Society Evolution sometimes characterized as “just a theory” That puts it on the same level as Atomic structure Gravitation Relativity Quantum mechanics The “Theory of Evolution” is two ideas: Evolution has occurred Mechanism of evolution: Natural Selection Evolution and the Origin of Life There has been a conflation of ideas by nonscientists: Evolution The Origin of life Origin of life is not known We have ideas, even some data Science does not address ultimate cause Evolution is a carefully documented idea Natural selection is a well supported scientific theory Natural Selection Basic premise: Excess reproduction Genetic variation exists: observable traits Not all offspring survive Better adapted to the environment will survive and reproduce more Survivors pass on their genetic information Differential survival/reproduction leads to changes in genetic structure of population Overall Pattern Differential survival and reproduction=natural selection Descent with modification Changes arise randomly: mutation Beneficial changes preserved by selection Accumulation of small changes lead to large changes over time What natural selection is not: Directional Purposeful Fitness Complex topic often misunderstood: survival of the fittest Does not mean winner of the Iron Man… Or the Boston Marathon, or even the Tour de France… Survival is important, but reproductive success is critical If you don’t leave any offspring, your fitness = 0! (note: ignores relatives) Macroevolution Ideas about how species arise and diversify Historical, unites paleontology and population biology Patterns of species distributions in time and space Speciation: appearance of new species Extinctions, mass and otherwise Homology and Analogy Homology: identity by descent, function may be the same, may not Structures derived from common ancestor Evolution within divergent lineages can lead to different function for homologous structure Analogy: function is the same, history is not Similar solution to same evolutionary problem Convergent evolution Example Consider forelimbs in vertebrate species Bones were all shared by common vertebrate ancestor Thus these bones are all homologous Different functions in different lineages Bats and birds both have wings... are these homologous??? No!!! Common ancestor was not winged. The bones are homologous but the wings are not Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Human Cat Bat Porpoise Horse Figure 22.17 Speciation For speciation to occur reproduction must be blocked Reproductive isolation Prezygotic Before fertilization Postzygotic After fertilization Genetic divergence requires reproductive isolation Reproductive Isolation Barriers to reproduction Pre-Zygotic Post-Zygotic Species A Mating Species B Habitat, Behavioral Isolation Fertilization Mechanical, Gametic Isolation Offspring Hybrid Breakdown Reduced Hybrid Viability, Sterility Three Domains DNA sequence data and analysis of rRNA have led to the recognition of 3 branches to the tree of life Call these Domains of life, above the level of kingdoms Eukarya Archaea Eubacteria Relationships Among Domains 3 domains represent the oldest divergence in the history of life Which occurred 1st? Eubacteria from Archaea and Eukarya Similarity of ribosome structure Analysis of rRNA genes Analysis of tRNA genes Similarity of gene expression Tree for Early History of Life Eukarya Archaea Eubacteria Lateral Gene Transfer This analysis is complicated by the observation of lateral gene transfer Eukaryotic genomes contain prokaryotic genes Eubacteria have archeal genes and visa versa Implies the early evolution of life may have been different than later events Lateral Gene Transfer Eukarya Archaea Eubacteria Phylogenetic Trees Express relationships graphically with tree diagrams Show relationships between groups Similarities and differences between groups Trees are expression of homolgous relationships Think about looking at: Twins Sibs Cousins Parazoa Radiata Porifera Cnidaria Ctenophora Platyhelminthes Eumetazoa Bilateria Echinodermata Hemichordata Chordata Deuterostomes Arthropoda Pentastomida Protostomes Nemerta Brachiopoda Sipunculida Pogonophora Mollusca Annelida Example Kingdom Phylum Class Order Family Genus Species Animalia Chordata Mammalia Primate Hominidae Homo H. sapiens
