Natural Selection and the Evidence for Evolution THE THEORY OF EVOLUTION Section Objectives: Summarize Darwin’s theory of natural selection. Explain how the structural and physiological adaptations of organisms relate to natural selection. Distinguish among the types of evidence for evolution. Charles Darwin and Natural Selection The modern theory of evolution is the fundamental concept in biology. Recall that evolution is the change in populations over time. Charles Darwin and Natural Selection Evolution Change in populations over time Charles Darwin H.M.S. Beagle Naturalist – study nature Galapagos Islands First started to realize that organisms change over time Darwin on HMS Beagle Worked on his ideas for over 2 decades Used Malthus’ idea that the human population would grow too large for the food supply Must struggle to compete for supplies Pigeon-breeding Artificial selection – similar to nat.selec. Breeding organisms w/ specific traits in order to produce offspring w/ desired traits Natural Selection Organisms w/ favorable variations survive, reproduce, and pass their variations to the next generation Alfred Wallace had similar ideas Advent of genetics further supports evolution Adaptations: Evolution Evidence for Adaptations develop over time Thorns or no thorns Distinctive coloring or plain Ex: mole-rats Those that live underground are blind have large teeth and claws Mimicry Enables one species to resemble another species Harmless species mimics a harmful species Ex: harmless fly and wasp Fig. 15.4 Camouflage Blend w/ surroundings Fig. 15.4C Most structural adaptations take millions of years to develop Physiological adaptations can be quicker Ex: Antibiotic resistant bacteria Penicillin no longer kills as many bacteria as it once did Also observed in insects and weeds (insecticides and pesticides) Physiological adaptations can develop rapidly The bacteria in a population vary in their ability to resist antibiotics. When the population is exposed to an antibiotic, only the resistant bacteria survive. The resistant bacteria live and produce more resistant bacteria. Today, penicillin no longer affects as many species of bacteria because some species have evolved physiological adaptations to prevent being killed by penicillin. Other Evidence of Evolution Fossils Provide a record of early life and evolutionary history Ex: ancestors of whales were probably landdwelling dog-like animals Record is incomplete Like a puzzle -> still understand the picture Table 15.1 evolution of camel Camel Evolution Age Organism Skull and teeth Limb bones Paleocene 65 million years ago Eocene 54 million years ago Oligocene 33 million years ago Miocene 23 million years ago Present Other Evidence of Evolution, Anatomy cont’d Homologous structures Structural features w/ a common evolutionary origin Ex: Fig. 15.6 forelimbs of crocodile, whale, and bird Analogous structures Structures that do not have a common evolutionary origin , but are similar in function Ex: bird wing and insect wing Crocodile forelimb Whale forelimb Bird wing Analogous Structures For example, insect and bird wings probably evolved separately when their different ancestors adapted independently to similar ways of life. Vestigial Structures Structure in a present day organisms that no longer serves its original purpose Ex: appendix, eyes of blind mole-rats, pelvic bones of whales Other Evidence of Evolution, cont’d Embryology Most embryos of different species look similar to each other Fig. 15.9 Embryology Pharyngeal pouches Pharyngeal pouches Tail Fish Tail Reptile Bird Mammal Other Evidence of Evolution, cont’d Biochemistry Nearly all organisms share DNA, ATP, and many enzymes (cytochrome c found from bacteria to bison to humans) Organisms that are more closely related have more similar cytochrome c Fig. 15.10 Organisms that are biochemically similar have fewer differences in their amino acid sequences. Biochemical Similarities of Organisms Comparison of Organisms Percent Substitutions of Amino Acids in Cytochrome c Residues Two orders of mammals 5 and 10 Birds vs. mammals 8-12 Amphibians vs. birds 14-18 Fish vs. land vertebrates 18-22 Insects vs. vertebrates 27-34 Algae vs. animals 57 Question 1 _______ is considered to be the fundamental concept of biology. A. genetics B. the modern theory of evolution C. artificial selection D. structural adaptation The answer is B. Question 2 Breeding organisms with specific traits in order to produce offspring with identical traits is called _______. A. B. C. D. natural selection adaptation mutation artificial selection The answer is D. Question 3 What is the difference between artificial selection and natural selection? Answer Artificial selection is the intentional breeding of organisms with specific traits in order to produce offspring with identical traits. Natural selection occurs when organisms with favorable variations of traits survive in nature, reproduce, and pass these favorable variations to offspring. Question 4 Mimicry and camouflage are NOT examples of _________. A. B. C. D. adaptation natural selection evolution artificial selection The answer is D. Question 5 How does mimicry differ from camouflage? Answer Mimicry is an adaptation that allows one species to resemble another species. Camouflage is an adaptation that allows one species to resemble its surroundings. Mechanisms for Evolution THE THEORY OF EVOLUTION Populations Genetics and Evolution Populations evolve, not individuals Natural selection acts on the range of phenotypes Gene pool All of the alleles in a pop Allelic frequency percentage of any specific allele in the gene pool Calculating Allelic Frequency Same way a baseball player calculates batting average Add up all of the alleles/by total # alleles Genetic Equilibrium Frequency of alleles remains the same over generations Changes in Genetic Equilibrium Any factor that affects the genes in a gene pool can change allelic frequencies = disruption in equilibrium = evolution Mutations – can be harmful or beneficial Radiation Genetic drift The alteration of allelic frequencies by chance events Can greatly affect small populations Only genes available to pass on to offspring Found in humans that have become isolated Amish population in Lancaster County, Pennsylvania Pop = 12,000 One of the original founders had the recessive allele for short arms and legs and extra fingers and toes. Fig. 15.12 Gene Flow Migration of individuals into and out of a populations Leave a pop = loss of genes in gene pool Enter a pop = gain genes in gene pool Natural Selection acts on Variations Traits have variations Eye color, height, skin color Some variations increase or decrease an organism’s chance of survival in an environment 3 types of natural selection that act on variation 1. Stabilizing Selection Favors average individuals in a pop Ex: spider size Too big = predators can find easily Too small = can’t get to food Average = more likely to survive, reproduce and pass on genes 2. Directional selection Favors one of the extreme variations of a trait Ex: woodpecker beak size Only those w/ long beaks can reach the bugs that live deep in the tree Long beaks would be an advantage over short beaks or average size beaks 3. Disruptive Selection Individuals w/ either extreme of a trait’s variation are selected. Ex: marine limpets Color from white, to tan, to dark brown Live attached to rocks which are light and dark Both the white and dark brown are camouflaged Disruptive Selection The Evolution of Speciation Species Occurs when members of similar populations no longer interbreed to produce fertile offspring Creates new species Geographic Isolation Physical barrier divides a population Examples? Reproductive Isolation Occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring Genes are so different that fertilization or the production of a fertile offspring does not occur Mating times differ Polyploidy Individual or species contains a multiple of the normal set of c’somes Caused by mistakes during cell division May result in immediate reproductive isolation Speciation Rates Rate at which new species arise Gradualism Gradual change of adaptations Ex: sea lilies Punctuated Equilibrium Occurs quickly, in rapid bursts Long periods of genetic equilibrium in between Patterns of Evolution Occur throughout the world Support evolution Divergent Evolution Where species become different from each other Based on needs of particular environment Adaptive Radiation, example An ancestral species evolves into an array of species to fit a number of diverse habitats Ex: Darwin’s finches, honeycreepers Adaptive Radiation Convergent Evolution Distantly related organisms evolve similar traits Share similar environmental pressures Ex: shark, penguin, dolphin Fish, bird, mammal Why do they look similar? Question 1 Which type of natural selection does NOT favor the evolution of new species? A. divergent B. disruptive C. stabilizing D. directional Question 2 Which type of natural selection does NOT favor the evolution of new species? A. divergent B. disruptive C. stabilizing D. directional Question 3 Why are the Galapagos Islands rich in unique species of organisms? A. The islands are an area exhibiting an abnormal number of mutations. B. The islands are geographically isolated. C. The island species have been subjected to increased gene flow. D. The island species have been subjected to stabilizing selection.