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Chapter 15 Tracing Evolutionary History PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko MAJOR EVENTS IN THE HISTORY OF LIFE © 2012 Pearson Education, Inc. Life’s Calendar Figure 15.4 Archaean eon Proterozoic eon Phanerozoic eon Colonization of land Animals Multicellular eukaryotes Single-celled eukaryotes Origin of Earth 4.6 Atmospheric oxygen Prokaryotes 4 3 2 Billions of years ago 1 Present 15.4 The origins of single-celled and multicelled organisms and the colonization of land were key events in life’s history Prokaryotes lived alone on Earth for 1.5 billion years, from 3.5 to 2 billion years ago. – During this time, prokaryotes transformed the atmosphere. – Prokaryotic photosynthesis produced oxygen that enriched the water and atmosphere of Earth. – Anaerobic and aerobic cellular respiration allowed prokaryotes to flourish. © 2012 Pearson Education, Inc. 15.4 The origins of single-celled and multicelled organisms and the colonization of land were key events in life’s history The oldest fossils of eukaryotes are about 2.1 billion years old. The common ancestor of all multicellular eukaryotes lived about 1.5 billion years ago. The oldest fossils of multicellular eukaryotes are about 1.2 billion years old. The first multicellular plants and fungi began to colonize land about 500 million years ago. © 2012 Pearson Education, Inc. 15.4 The origins of single-celled and multicelled organisms and the colonization of land were key events in life’s history Humans diverged from other primates about 6 to 7 million years ago. Our species, Homo sapiens, originated about 195,000 years ago. If the Earth’s history were compressed into an hour, humans appeared less than 0.2 seconds ago! © 2012 Pearson Education, Inc. Larger Cells and Organisms Need More Oxygen More O2 allows for CR and aerobic metabolism = greater ATP yield!! Molecular Homologies Provide Greatest Evidence for Life’s Common Ancestor All living organisms share many biochemical and developmental pathways: DNA --> RNA --> Protein Same genetic code Transcription/translation/replication processes same Glycolysis and cellular respiration similar Many genes are amazingly similar – About 99% of the genes of humans and mice are homologous. – About 50% of human genes are homologous with those of yeast. © 2012 Pearson Education, Inc. Three Domain System Molecular homologies have unveiled a new organization to life’s history. Comparison of rRNA gene sequences by Carl Woese Remember, rRNA gene sequences allow for comparison of long-distance relationships Biologists currently recognize a three-domain system consisting of – two domains of prokaryotes: Bacteria and Archaea, and – one domain of eukaryotes called Eukarya including – fungi, protists, plants, animals © 2012 Pearson Education, Inc. Figure 15.19A 1 Most recent common ancestor of all living things 2 Gene transfer between mitochondrial ancestor and ancestor of eukaryotes 3 Gene transfer between chloroplast ancestor and ancestor of green plants Bacteria 3 2 1 Eukarya Archaea 4 3 2 Billions of years ago 1 0 Figure 1.4 The Tree of Life Implications of Updated Tree of Life Bacteria and Archaea diverged very early in the evolutionary history of life Archaea are more closely related to eukaryotes than to bacteria. Eukarya diverged from line of Archaea Several endosymbiotic events lead to evolution of eukaryotes Mitochrondria acquired from aerobic bacteria Chloroplast from photosynthetic bacteria Mitochondria acquired first; 1st eukaryotes heterotrophic Multicellularity in eukaryotes arose multiple times (convergent evolution) © 2012 Pearson Education, Inc. Endosymbiosis theory Mitochondria & chloroplasts were once free living bacteria engulfed by ancestral eukaryote Endosymbiont cell that lives within another cell (host) as a partnership evolutionary advantage for both one supplies energy the other supplies raw materials & protection Honors Biology Lynn Margulis U of M, Amherst Endosymbiosis theory Evolution of eukaryotes Honors Biology