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• All living things share a common ancestor. • We can draw a Tree of Life to show how every species is related. • Evolution is the process by which one species gives rise to another and the Tree of Life grows • The theory of Evolution deals with how evolution happens. Our understanding of this process is always changing. • Evolution is also a fact as there is a huge amount of indisputable evidence for its occurrence. 1809 - 1882 Most influential contributor to thoughts about evolution The Origin of Species 1859 Presented evidence for changes in species through Natural Selection Galapagos Islands Most scientists in Darwin’s day thought the Earth was only a couple thousand years old They believe that Earth had not changed, nor had any of its species Helped scientists recognize that Earth is many millions of years old and the processes that changed Earth in the past are the same ones operating now – hypothesis regarding geological forces that have shaped Earth – past events that affected the earth are still happening One of the first scientists to recognize that living things have changed over time Species were descended from other species Also realized that organisms had adapted to their environment By selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime The idea that organism’s alter their body by using it in new ways Believe acquired traits could be inherited If an organism’s body was altered, it would pass that trait to its offspring Example? 5 year round-the-world voyage 1831 - at age 22 H.M.S. Beagle Ship’s naturalist At beginning of trip - believed species were immutable Collected and examined the species that inhabited the regions the ship visited Fossils, coral ,plants, animals Volcanic islands - 3.5 mya Isolated, west of Ecuador All inhabitants are descended from species that arrived on islands from elsewhere Finches Tortoises Iguanas Blue-footed Booby 13 species of finches Share many morphological features Differ in several ways Beak size Beak shape Food eaten Evolved from a single species He attempted to correlate variations in their traits with environmental challenges WET ISLANDS Short neck Domed shell Long neck Flared shell DRY ISLANDS Marine Iguana Algae eater Land Iguana Terrestrial vegetation The characteristics of many animals and plants varied noticeably among the different islands of the Galapagos Darwin’s Evolutionary Ways of Thinking Darwin publishes Origin Of Species Prompted after Wallace publishes essay Words/phrases we are introduced to Artificial selection Struggle for existence Fitness Adaptation Survival of the fittest Nature provides variation, humans select variation that they found useful Livestock Members of the same species compete What are they competing for? What Darwin called the ability of an individual to survive and reproduce Fitness is a result of adaptation Adaptation any inherited characteristic that increases an organism’s chance of survival Individuals with characteristics that are better suited to their environment – adaptations that enable their fitness – survive and reproduce most successfully Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment Principle proposed by Darwin Over long periods of time, natural selection produces organisms that have different structures, establish different niches, or occupy different habitats RESULT species today look different from their ancestors All species, living and extinct, are derived from a common ancestor A single “tree of life” links all living things! Darwin argued living things have been evolving on Earth for millions of years Evidence for this process can be found: ▪ Fossil record ▪ Geographical distribution of living species ▪ Homologous structures of living organisms ▪ Similarities in embryology Fossils remains of ancient life Darwin compared fossils from older rock layers to those in younger rock layers to document the change of life on Earth © World Health Org. en.wikipedia.org/wiki/Image:Eopraptor_sketch5.png © NASA origins bacteria complex cells dinosaurs humans The fossil record shows a sequence from simple bacteria to more complicated organisms through time and provides the most compelling evidence for evolution. Species living on different geographical areas had each descended from different ancestors However, because of similar ecological conditions they were exposed to similar pressures of natural selection similar features Structures that have different mature forms in different organisms, but develop from the same embryonic tissue. Organs of many species are so reduced in size that they are just traces of homologous organs in other species Examples: miniature legs, tails Appendix Wisdom Teeth Tailbone Particular Ear Muscles VNO Plica semilunaris Embryology of many animals with backbones are very similar WHAT DOES THIS MEAN? Certain embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates At one point… you looked like this. Thought you should know… Individuals organisms differ, and some of this variation is heritable Organisms compete for resources Each organism has different advantages/disadvantages organisms best suited survive and pass their traits to offspring Species today are descended with modification from ancestral species; common ancestor, single tree of life Evolution of Populations When Darwin developed this theory of evolution he had no idea how heredity worked This left him unable to explain: Source of variation How inheritable traits are passed through generations Evolutionary biologists connect Mendel and Darwin’s work in the 1930s Gene pool: consists of all genes, including all the different alleles, that are present in a population Typically contain traits with two or more alleles When studying evolution today, biologists often focus on a particular Evolution of populations is called In genetic terms, evolution is any change in the relative frequency of alleles in a population : # of times the allele occurs in a gene pool Can occur because of: ▪ mistakes in replication ▪ environmental chemicals May or may not affect an organism’s : recombination of genes that occurs during production of gametes Causes most inheritable differences between relatives As a result, sexual reproduction is a major source of variation in organisms Despite gene shuffling, the frequency of alleles does not change in a population Similar to a deck of cards – no matter how many times you shuffle, same cards (alleles) are always there. controlled by single gene with two alleles Ex.) widow’s peak, hitchhiker’s thumb, tongue rolling : controlled by 2 or more genes, each with 2 or more alleles Examples: height, hair color, skin color, eye color single gene polygenic Only two phenotypes possible Multiple (many) phenotypes possible tongue roller or non-tongue roller height range 4feet to 9 feet all Natural selection affects polygenic traits through: Single phenotype is favored, causing the allele frequency to continuously shift in one direction. Individuals with highest fitness: those at one end of the curve Key Directional Selection Food becomes scarce. Low mortality, high fitness High mortality, low fitness Individuals at the center of the curve have highest fitness; evolution keeps center in the same position but narrows the curve Average phenotype : human birth weight Stabilizing Selection Key Low mortality, high fitness High mortality, low fitness Birth Weight Selection against both extremes keep curve narrow and in same place. Individuals at both ends of the curve survive better than the middle of the curve Natural selection favors extreme phenotypes Individuals with highest fitness: both ends of curve : birds where seeds are either large or small Disruptive Selection Largest and smallest seeds become more common. High mortality, low fitness Population splits into two subgroups specializing in different seeds. Beak Size Number of Birds in Population Low mortality, high fitness Number of Birds in Population Key Beak Size Evolution of Populations Natural selection is not the only source of evolutionary change. In small populations, an allele can become more or less common by chance Genetic drift: random change in allele frequency that occurs in small populations So, genetic drift and natural selection both involve changes in allele frequencies 1. Founder Effect 2. Bottleneck Effect Allele frequencies change due to migration of a small subgroup of a population Founder Effect: Beetles on Hawaiian islands Sample of Original Population Descendants Founding Population A Founding Population B Major change in allele frequencies when population decreases dramatically due to catastrophe Hunted to near extinction ♦ Population decreased to 20 individuals in 1800’s ♦ Those 20 repopulated so today’s population is roughly 30,000 ♦ No genetic variation in 24 genes ♦ Catastrophe Original population Surviving population The formation of new biological species, usually by the division of a single species into two or more genetically distinct one. 1. 2. 3. Kaibab Squirrel Abert Squirrel Kaibab Squirrel Abert Squirrel Two populations are capable of interbreeding but do not interbreed because they have different ‘courtship rituals’ or other lifestyle habits that differ Eastern and Western Meadowlark populations overlap in the middle of the US Male birds sing a mating song that females like East and West have different songs Females only respond to their subspecies song. Populations reproduce at different times Mates in: Mates in: April July Geographic, Behavioral, and Temporal Isolation are all believed to lead to speciation. : large-scale evolutionary patterns and processes that occur over long periods of time Six important topics Extinction Adaptive radiation Convergent evolution Coevolution Punctuated equilibrium Changes in developmental genes More than of all species that have ever lived are now extinct Several times in Earth’s history – Examples of mass extinctions and their causes? What effects have extinctions had? Bursts of evolution! Convergent Evolution Process by which unrelated organisms come to resemble one another Pattern of long, stable periods interrupted by brief periods of rapid change Why would rapid change occur? Isolation Migration Extinction Changes in genes for growth and differentiation during embryological development could produce transformations in body shape and size : insects Anna Marie, Brandon - Baltra (South Seymour) Island Hunter, Shalom - Española (Hood) Island Joshua, Lindsey - Fernandina (Narborough) Island Gabe, Matt - Floreana (Charles or Santa María) Island Kerrington, Tiana - Genovesa (Tower) Island Aurora, Shannon - Pinzón (Duncan) Island Kyle, Taylor - San Cristóbal (Chatham) Island Alastair, Tenko - Santa Cruz (Indefatigable) Island Erin, Abby - Santiago (San Salvador, James) Island Diego, Curtis - Pinta (Abingdon) Island Susan, Ethan - Santa Fé (Barrington) Island Justin, John, Robert - Isabela (Albemarle) Island Jordan, Colton, Lauren - Santa Cruz (Indefatigable) Island Avelyn, Daniel, Freeman - Española (Hood) Island Clarissa, Christina, Blake - Genovesa (Tower) Island Stella, Grant, Ben Hagan - Santiago (San Salvador, James) Island Bruce, Ryan, Griggs - Fernandina (Narborough) Island Jokima, Madison, Penny - San Cristóbal (Chatham) Island Fahim, Ronnie, Hanna - Pinta (Abingdon) Island Edgar, Olivia, Julien - Marchena (Bindloe) Island Drew, Shayna, Dove - Pinzón (Duncan) Island