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The Origin and Evolutionary History of Life Conditions on Early Earth ◦ Age of Earth ~4.6 billion years ◦ Atmosphere had free No O2 Rich in CO2, H2O, CO, H2, N2 Also ammonia (NH3), sulfuric acid (H2S), methane gas (CH4) ◦ Presence of oxygen (photosynthesis) ◦ Increased sun energy ◦ Formation of organic compounds ◦ Sufficient time Protobionts appeared first. They are considered to have possibly been the precursors to prokaryotic cells. Then appeared heterotrophic bacteria that fed on organic molecules & carried anaerobic fermentation Protobiont Heterotrophic Bacteria Cyanobacteria split water molecules and released oxygen through photosynthesis. This bacteria accounts for much of the oxygen in our atmosphere. Endosymbiontic Theory Mitochondria and chloroplasts derived from prokaryotes A prokaryote ingested but not digested, some aerobic bacteria Over along time the aerobe became mitochondria This also happened with a cyanobacteria, which became chloroplast Reproduced along with host cell Endosymbiontic Theory Introduction to Darwinian Evolution Important Terminology Evolution Accumulation of inherited changes within populations over time Population Group of individuals of one species that live in the same geographic area at the same time Species Group of organisms with similar structure, function, and behavior capable of interbreeding Pre-Darwinian Ideas Aristotle (384–322 B.C.E.) Saw evidence of natural affinities Leonardo da Vinci (1452–1519) Correctly interpreted fossil rocks Jean Baptiste de Lamarck (1744–1829) First to propose that organisms undergo change as a result of natural phenomenon Lamarck ideas discredited when Mendel’s theories rediscovered around 1900 Darwin & Evolution Voyage of the H.M.S. Beagle 1831 Basis for Darwin’s theory of evolution Darwin observed similarities between animals and plants ◦ Arid Galapagos Islands ◦ Humid South American mainland Voyage of the H.M.S. Beagle Influences on Darwin Principles of Geology by Lyell Artificial selection Breeders developing many varieties of domesticated animals in a few generations Plant varieties, such as kale and broccoli, developed from wild cabbage Ideas of Thomas Malthus Population growth not always desirable Population increases geometrically; food supply increases arithmetically Based on adaptations by organisms over time: Inherited variations favorable to survival persevere Unfavorable variations are eliminated Theory of Evolution by Natural Selection Proposed by both Darwin and Wallace Based on four observations: 1. Genetic variation exists among individuals 2. Reproductive ability of species causes its population to increase 3. Organisms compete for resources 4. Offspring with most favorable characteristics is most likely to survive Genetic variation in emerald tree boas 1. 2. 3. 4. 5. Fossil Record Comparative Embryology Comparative Anatomy Biogeography DNA Homology Direct evidence of evolution comes from fossils Shows life has evolved through time Exposed layers of sedimentary rock Fossils develop in different ways Fossil intermediates in whale evolution Determining the age of fossils: radioisotope decay Evidence for evolution from comparative anatomy Homologous features Derive from same structure in common ancestor Vestigial structures Remnants of structures indicating adaptation Homology in plants Convergent evolution: mammals who eat ants and termites Vestigial structures Evidence of Evolution from Biogeography ◦ Study of past and present geographic distribution of organisms ◦ Continental drift has played a major role in evolution Continental drift Evidence for evolution from developmental biology Proteins and DNA contain record of evolutionary change Phylogeny Evolutionary history of group of related species Phylogenetic trees Diagrams showing lines of descent based on molecular data Phylogenetic tree of whales and their closest living relatives Intergenerational changes in allele or genotype frequencies within a population Often involves relatively small or minor changes, usually over a few generations Changes in allele frequencies of a population caused by microevolutionary processes: 1. 2. 3. 4. 5. Nonrandom mating Mutation Genetic drift Gene flow Natural selection Nonrandom Mating Inbreeding Increases the frequency of similar alleles Prevents genetic variation Mutation Source of new alleles in a population Increases genetic variability acted on by natural selection Genetic drift Random change in allele frequencies of a small population Decreases genetic variation within a population Changes it causes are usually not adaptive Ex: Polydactyl traits in Northern Amish Communities Genetic drift Bottleneck is a sudden decrease in population size caused by adverse environmental factors Founder effect is genetic drift occurring when a small population colonizes a new area Gene flow Movement of alleles caused by migration of individuals between populations Causes changes in allele frequencies Natural selection 1. 2. 3. Causes changes in allele frequencies leading to adaptation Operates on an organism’s phenotype Changes genetic composition of a population favorably for a particular environment Modes of Natural Selection Stabilizing Selection ◦ Favors the mean (average individuals) ◦ Favors the “already well-adapted organisms” ◦ If the environment remains unchanged, the “fittest” organisms will also remain unchanged Ex: Horseshoe Crabs & Ginkgo Trees(have not changed for millions of years) Directional Selection ◦ Favors one phenotypic extreme over the others and eventually leads to change in a population. ◦ It occurs when organisms must adapt to changes conditions in the environment. Ex: Pesticide & antibiotic resistance (organisms learn to adapt and withstand a harmful chemical) Disruptive Selection ◦ Favors two or more phenotypic extremes. ◦ Ex: African orange butterflies can range in color from orange to blue. The orange and blue forms mimic foul-tasting species, so predators avoid them. The colors in-between do not ward off predators, so butterflies with those colors are eaten more commonly. As a result, only butterflies with extreme colors (orange & blue) survive. Modes of Natural Selection (a) No selection (b) Stabilizing selection Modes of Natural Selection (c) Directional selection (d) Disruptive selection Genetic variation in populations caused by: 1. 2. Mutation Sexual reproduction ◦ Allows new phenotypes Speciation & Macroevolution Reproductive Isolating Mechanisms Prevent gene flow between species. Two types: 1. Prezygotic Barriers Prevent mating or fertilization. 2. Postzygotic Barriers Reproductive failure after fertilization 1. 2. 3. 4. 5. Temporal Isolation Habitat Isolation Gametic Isolation Begavioral Isolation Mechanical Isolation 1. Temporal Isolation Mating at different times of year Mating at different times of day 2. Habitat Isolation ◦ Different habitats in the same area 3. Gametic Isolation ◦ Incompatible egg and sperm ◦ Molecular recognition on the surface of the cells 4. Behavioral (sexual) Isolation ◦ Required courtship behaviors The male satin bowerbird builds a bower of twigs (a dark tunnel) to attract females 5. Mechanical Isolation ◦ Incompatible genital organs Only small bees can land on the petal of the black sage Only large bees brush against the stamens of the white sage Hybrid Inviability Zygote forms, but hybrid embryos die when genetic regulation fails during development Hybrid Sterility problems during meiosis cause abnormal gametes Hybrid Breakdown Hybrid cannot reproduce because of some defect Formation of New Species: Speciation When a population becomes reproductively isolated the separated gene pools diverge & genetic exchange stops, as a result a new species is formed Types of Speciation Mechanisms: 1. 2. 3. Allopatric Speciation Sympatric Speciation Artificial Speciation Allopatric Speciation a population splits into two geographically isolated populations (for example, by habitat fragmentation due to geographical changes or social change such as emigration). Most common form of speciation Genetic drift in small populations Examples: 1. Galapagos tortoises that live in separate, but nearby islands 2. Squirrel species separated by the Grand Canyon Abigdoni Tortoises Chathamensis Tortoises Porteri Tortoises Squirrel species separated by the Grand Canyon have diverged in fur color Sympatric speciation Refers to the formation of two or more descendant species from a single ancestral species all occupying the same geographic location Populations diverge and each occupies a new ecological niche Examples: 1. Finches in Galapagos Islands 2. Maggot Flies in North America The finches live in the same habitat but each has a different niche. Fossil record often lacks transitional forms between two species Is the fossil record simply incomplete? Or does it accurately reflect evolution as it really occurs? Long periods of stasis (~2 My) Punctuated by periods of rapid speciation (~100,000 y) Triggered by changes in the environment Abrupt appearance of new species in the fossil record Continuous evolution over long periods The traditional view Populations gradually accumulate adaptations Different selective pressures in different environments Gradualism Punctuated Equilibrium Large-scale phenotypic changes in populations, classified at the species level or higher Characterized by: 1. Appearance of evolutionary novelties 2. Adaptive Radiation Patterns 3. Mass extinctions Allometric Growth ◦ Varied rates of growth for different parts of the body ◦ A change in development can result in a new species when the change is adaptive Allometric Growth Paedomorphosis Retention of juvenile characteristics in the adult A change in the timing of development Paedomorphosis in an axolotl salamander Adaptive Radiation Speciation fills new ecological niches New adaptive zones may appear when the environment changes One species colonizes an island and diversifies into new species Adaptive radiation Extinction of Species Facilitates evolution by opening adaptive zones Background extinction at a steady rate Mass extinctions Five or six mass extinctions of many species and higher taxonomic groups Major climate changes Catastrophes such as asteroid impacts Mass extinction of the archosaurs The Evolution of Primates Primate evolution All Mammals Endothermic (warm blooded) Body hair Feed young with milk from mammary glands Most are viviparous (give live birth) Placental Mammals Placenta exchanges materials between mother and fetus Newborns are more developed than marsupials ALL Primates: Are mammals Have 5 grasping digits Have pposable thumb or toe Have long, freely moving limbs Have eyes in front of the head Have large brains Primate hands and feet Suborder Prosimii ◦ Lemurs Suborder Tarsiiformes ◦ Tarsiers Suborder Anthropoidae ◦ Monkeys, apes, humans Anthropoids Old and new world monkeys Apes and humans Hominoids Apes Gibbons Orangutans Gorillas Chimpanzees Humans New world monkey Old world monkey Hominids Humans & extinct human ancestors Differences between ape and human skeletons Human adaptations for bipedal life on the ground Complex curvature of the spine Shorter, broader pelvis Foramen magnum at base of skull First toe aligned with other toes Human and Gorilla Skeletons Human and Gorilla Heads