Transcript Evolutionx
Evolution BIG Idea Evolution is the result of many random processes selecting for the survival and reproduction of a population Evolution is not a theory of how life first formed. It is a theory that explains how species change over time. Law- Generalizes a body of observations. At the time it is made, no exceptions have been found to a law. It explains things but does not describe them. Ex: F= m x a Theory- An explanation of observable phenomena based on available empirical data and guided by a system of logic that includes scientific laws; provides a system of assumptions, accepted principles, and rules of procedure devised to analyze, predict, or otherwise explain the nature or behavior of a specific set of phenomena. A theory not only explains known facts; it also allows scientists to make predictions of what they should observe if a theory is true. Scientific theories are testable. New evidence should be compatible with a theory. If it isn't, the theory is refined or rejected. The longer the central elements of a theory hold--the more observations it predicts, the more tests it passes, the more facts it explains--the stronger the theory. Lamarck (1744-1829) was first to state that descent with modification occurs and that organisms become adapted to their environments Inheritance of acquired characteristics was the Lamarckian belief that organisms become adapted to their environment during their lifetime and pass on these adaptations to their offspring Lamarck believed that the long necks of giraffes evolved as generations of giraffes reached for ever higher leaves; known as the Law of Use & Disuse Darwin's Background & Voyage: •His nature was too sensitive • to become a doctor like his father •so he studied divinity •He attended biology and geology lectures and was tutored by the Reverend John Henslow who arranged his trip on the HMS Beagle •In 1831, at the age of 22, Charles Darwin accepted a naturalist position aboard the ship HMS Beagle & began a five-year voyage around the world •He read Principles of Geology by Charles Lyell that stated that the observed massive geological changes were caused by slow, continuous processes (erosion, uplifting...) •Darwin carried this book with him on his voyage as he witnessed Argentina coast earthquakes raising the earth several feet, & marine shells occurring far inland and at great heights in the Andes •Darwin's many observations led him to the idea that species slowly change over time. The Galapagos Islands: Volcanic islands off the South American coast Island species varied from the mainland species, and from island-to-island Each island had either long or short necked tortoises depending on the island's vegetation Darwin's comparison of the animals of South America and the Galapagos Islands caused him to conclude that adaptation to the environment can cause diversification, including origin of new species Finches on the Galapagos Islands resembled a mainland finch, but there were more types Bill shapes are adaptations to different means of gathering food. Galapagos finch species varied by nesting site, beak size, and eating habits Darwin's Theory of Evolution: An adaptation is a trait that helps an organism be more suited to its environment Adaptations develop over time. On the Origin of Species by Darwin: After the HMS Beagle returned to England in 1836, Darwin waited over 20 years to publish Origin of Species . Conclusion: Natural selection is the mechanism by which species change and new species arise Darwin’s Main Points of Natural Selection 1. A population has variations. 2. Some variations are favorable. 3. More offspring are produced than survive. 4. Those that survive have favorable traits. 5. A population will change over time. As a result… Evolution by natural selection leads to adaptations in a population. ***This does not mean that individuals change, but that favorable traits are passed down so future generations display the favorable adaptations. Fitness is a measure of an organism's reproductive success. Organisms most fit to reproduce are selected by environment which results in adaptation of the population. *Natural selection is also called "survival of the fittest." Extinction occurs when previous adaptations are no longer suitable to a changed environment. BIG Ideas in Biology 9. DNA segments contain information for the production of proteins necessary for growth and function in cells Allele Alternative form of a gene for each variation of a trait Ex: B= brown eyes b= blue eyes Genotype Genetic makeup (genes) of an organism determined by a pair of alleles Phenotype Observable characteristics (trait) Ex: blue eyes, brown hair Gene Pool Total genes (alleles) in a population at any one time What process affects the alleles in the gene pool? Natural selection!!!! Mutation: Changes in DNA Sequence Another driving force but it is RANDOM Mutations which alter DNA, alter Proteins then Traits Most mutations are evolutionarily NEUTRAL Evidence For Evolution 1. Adaptations 2. Fossils 3. Comparative Anatomy 4. Comparative Embryology 5. Comparative Biochemistry 6. Biogeography Fossil Evidence: Fossils are relics or impressions of ancient organisms Most fossils are found in layers (strata) of sedimentary rock. The fossil record traces history of life and allows us to study history of particular organisms Through radiometric dating, geologists estimate the age of the earth at about 4.6 billion years Fossils are at least 10,000 years old and include skeletons, shells, seeds, insects trapped in amber, imprints of organisms, organisms frozen in ice (wooly mammoth), or trapped in tar pits (saber-toothed tiger) Transitional forms reveal links between groups (Example: Therapsids were mammal-like reptiles and Pterosaurs were bird like reptiles) Tiktaalik Ambulocetus FOSSILS Environments in every area have changed drastically Seashell fossils in PA PA is NOT a beach… 3. Comparative Anatomy Homologous structures-similar features that originated in a shared ancestor. One bone, two bones, many bones. 3. Comparative Anatomy Analogous Structures: Look similar but are different Different SAME ancestor FUNCTION Homologous vs. Analogous Category Homologous Evolved from Common Ancestor? Evolved Independently? Similar Underlying Structure Different Underlying Structure Used for Different Function Used for Same Function Analogous Vestigial Structures Vestigial Serves Structures: NO function Useful to ancestors…not useful for modern organism http://io9.com/5829687/10-vestigialtraits-you-didnt-know-you-had 4. Comparative EmbryologyALL Vertebrates have a common ancestor 5.Comparative Biochemistry Species Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide 100% Human Rhesus monkey 95% Mouse 87% Chicken 69% Frog re 22.16 Lamprey 54% 14% Similar DNA sequences… …similar genes… ….code for similar traits! In closely related species 6. Biogeography Geologic theory: (plate tectonics) Continental masses were one land mass that explains closely related species have common ancestors on now separated continents Bio geographical Evidence: Biogeography is the study of the geographic distribution of life forms on earth Physical factors, such as the location of continents, determine where a population can spread Example: Placental mammals arose after Australia separated from the other continents, so only marsupials diversified in Australia Other Evolution Info: Speciation: process by which new distinct species evolve Occurs when 1 population is isolated from another population (geography/reproduction) DIVERGENT EVOLUTION- two or more species originate from same species and become increasingly different over time CONVERGENT EVOLUTION – development of similar structures in organisms that do not share recent common ancestor a)divergent b)convergent Genetic Drift A change in the allele frequency of a population as a result of chance events rather than natural selection. Examples: Population Founder Bottleneck Effect Population Bottleneck Occurs when a population’s size is reduced for at least one generation. Reduced genetic variation means that the population may not be able to adapt to new selection pressures, such as climatic change or a shift in available resources. Population Bottleneck Example Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted. Northern Elephant Seal Population Bottleneck Founder Effect A decrease in genetic variation caused by the formation of a new population by a small number of individuals from a larger population. Founder Effect Example The Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. Founder Effect Gradual Evolution vs. Punctuated Evolution Examples of Evolution in Modern Times: Peppered moth -light colored vs. dark colored (industrialization influence) Manchester, England Insect resistance to insecticides Bacterial resistance to antibiotics