Evolution History of Thought Linnaeus: Taxonomy Developed first taxonomic system naming and classifying the diverse forms of life for the greater glory of God : Hutton: Gradualism profound changes in the Earth s features; cumulative, slow process Lamarck: Evolution Through Use & Disuse believed, incorrectly, that body parts could change due to use and disuse and that these acquired characteristics could be inherited. Malthus: Populations human suffering was due to increasing populations Cuvier: Paleontology Paleontologist that recognized that many extinctions occurred... he argued it must have been due to catastrophism Lyell: Uniformitarianism Geologist that argued geologic processes have not changed throughout Earth s history Darwin: Evolution by Natural Selection Published The Origin of Species Believed natural selection was the driving force for evolution. Mendell: laws of inheritance provided explanation for selection process The Historical Context of Darwin s Life and Ideas Charles Darwin Darwin originally studied medicine and theology Darwin was hired as Naturalist aboard the H.M.S. Beagle Traveled 5 years around South America, Europe, Africa, and Australia collecting fossils Became famous for work with the Galapagos finches he believed that all the finches of these islands were originally part of the same species (common ancestor) Wrote "On the Origin of Species" (1858) The Voyage of the HMS Beagle (1831 1836) Evolution by Natural Selection Evolution a change in the frequency of alleles (genes) in a population over time There are two areas of evolutionary study: 1. Microevolution how populations of organisms change from generation to generation and how new species originate 2. Macroevolution patterns of change in groups of related species over broad periods of geologic time. These patterns determine phylogeny (the evolutionary relationships among species) Darwin discovered that most of the animal species on the Galapagos lived nowhere else in the world, but they resembled species on the South American mainland Natural selection differential survival and reproduction among individuals in a population based on inheritable traits. The most well suited organisms survive and reproduce at a greater rate, thus eventually changing the allelic frequencies of the population 1
Evolution Chpt 13, 14, 15 Teacher Version.notebook Evolution by Natural Selection Example of Natural Selection: Insecticide Resistance in Insect Pops. How it works: 1. Mutations, crossing over, etc... lead to genetic variation 2. Genetic variation exists in all populations 3. Struggle for existence (survival) populations will always reproduce at a greater rate than the environment can support, thus leading to competition 4. Some organisms possess variations that make them better able to survive and reproduce than others. Darwin would say these organisms are more fit. (survival of the fittest). 5. Over time, these variations will continue to be passed on and will eventually change the population Example of Evolution: Drug Resistance in HIV 3TC interferes with reverse transcriptase Patterns of Selection Natural selection can impact a population in a variety of ways: Directional selection favors traits at one extreme Stabilizing selection favors individuals with the middle phenotype Diversifying selection favors both extremes 3TC mimics cytosine and when inserted it terminates further elongation HIV viruses that are resistant to 3TC have a different form of reverse transcriptase, it can recognize the difference in cytosines Influencers of Natural Selection Evolution (change in allele frequencies) can be driven by: In order for natural selection to operate, there must be genetic variation among individuals in a population. It comes from: Mutations change in DNA Sexual reproduction crossing over independent assortment random joining of gametes from two individuals Diploidy allows one gene to be hidden Changes in the environment Gene flow alleles entering or leaving the population due to emigration or immigration Nonrandom mating In breeding Breeding based on proximity Sexual selection preferential mating with males or females with specific traits or behaviors Usually leads to male competition and female choice. Often leads to sexual dimorphism differences in the appearance of males and females Ex: manes in lions, plumage in birds 2
Influencers of Natural Selection Genetic drift changes in the gene pool of a small population Three types: 1. Changes due to random chance 2. Founder effect when a few individuals migrate and start their own population, which doesn t represent the genes in the original population 3. Bottleneck effect when a population undergoes a dramatic decrease in size (due to natural disasters, for example) and the individuals left don t represent the original population The "Bad" Traits...Why Aren't They All Gone? Natural selection should extinguish a population's variation by getting rid of the unfavorable phenotypes...so why doesn't variation disappear? Techniques to Preserve or Restore Variation: 1.) Diploidy heterozygote condition hides the recessive form; prevents it from being lost 2.) Balanced polymorphism the frequencies of coexisting forms do not change noticeably over many generations Causes of balanced polymorphism: 1.) Heterozygote advantage better reproductive success than homozygotes 2.)Hybrid vigor increased vitality of hybrid offspring ex. Sickle cell anemia heterozygotes are resistant to malaria ex. Plant Crops homozygotes are more sensitive to disease Gene Pool all possible alleles of all members of a population Hardy Weinberg Theorem: the frequencies of alleles in a population's gene pool will remain constant over generations as long as the following conditions are met: There can be no natural selection Mutations cannot occur The population must be isolated (no gene flow) The population must be large (no genetic drift) Mating must be random If any of those 5 things are violated the populations allele frequencies will change the population will evolve. The Hardy Weinberg equation is used to evaluate whether or not the population is evolving. It is determined using the following values: Allele frequencies for each allele P= % of dominant gene Q= % of recessive gene Genotypic frequencies: P2= % of homozygous dominant individuals Q2= % of homozygous recessive individuals 2PQ= % of heterozygous individuals The equations: P + Q = 1 (all alleles add up to 100%) P2 + 2PQ + Q2= 1 (all individuals add up to 100%) Species a group of individuals that can interbreed and produce live, fertile offspring Speciation the formation of a new species that are reproductively isolated Anagenesis one species evolves into a new one Cladogenesis one species diversifies and gives rise to new species 3
Reproductive Isolation The following are all reasons why two organisms may NOT be able to reproduce and/or produce live, fertile offspring They are therefore NOT part of the same species Some are pre zygotic (before a zygote forms): Spatial isolation species don t encounter one another Temporal isolation when species mate or flower during different seasons or different times of the day Behavioral isolation when a species doesn t recognize another species as a mating partner because it doesn t perform proper courtship rituals (songs, scents, etc.) Mechanical isolation the male and female genitalia are structurally incompatible Gametic isolation when male gametes are incapable of penetrating the female gamete Some are post zygotic (after a zygote forms): Hybrid inviability when the zygote fails to develop and dies before birth Hybrid sterility when the hybrid is born but isn t able to have it s own children Hybrid breakdown when the hybrids live for a generation, but aren t well suited to the environment and die out Can occur in several ways: Allopatric speciation Sympatric speciation Adaptive radiation Allopatric Speciation begins when a population is divided by a geographic barrier (such as a mountain or river). The two populations now become different as each evolves to the different environments. EX. Pupfish lakes/rivers go through drying trend EX: Grand Canyon Squirrels Sympatric Speciation occurs without the presence of a geographic barrier. EX: polyploidy in plants. Autopolyploidy more than 2 sets of chromosomes result of self fertilization can't interbreed with diploid plants may be able to self fertilize Adaptive Radiation when one species rapidly evolves into many species. Happens when colonizing a new, diverse geographic area Allopolyploidy more than 2 sets of chromosomes hybrid of 2 different species very common more vigorous than parents 4
Patterns of Evolution Divergent evolution when two species that originate from a common ancestor speciate. Example African and Indian elephants speciated Convergent evolution when two unrelated species share similar traits due to similar environmental conditions (analogous traits) Example the torpedo body shape of penguins and porpoise Parallel evolution two related species that have made similar evolutionary changes after diverging from a common ancestor. Example placental and marsupial mammals Coevolution when two species evolve in response to each other. Examples predator/prey relationships or relationships between plants and pollinators Macroevolution The Geologic Time Scale Macroevolution Macroevolution Timing of Macroevolution There are two distinct theories used to interpret fossil evidence for evolutionary history: Gradualism argues that evolution occurs by the gradual accumulation of small changes. Punctuated equilibrium argues that evolutionary history has long periods of stasis (stability with little or no evolution) followed by brief periods of rapid evolution. Artificial Selection Artificial Selection selection carried out by humans for desirable traits. Have led to various breeds of dogs. Brussel sprouts, broccoli, cabbage and cauliflower all originated from a single wild plant. 5
Evolution Chpt 13, 14, 15 Teacher Version.notebook Paleontology fossil evidence shows gradual changes in species, species that are now extinct, and transitional fossils Law of Superposition allows for relative dating deeper fossils are older Transitional Fossils fossils that show intermediate forms Biogeography geographic distribution of species species in different regions of the world look alike, especially when in similar environments Embryology reveals similar stages in development among species. EX: gill slits form in fish, chicken, pig and human embryos Vestigial structures: historical remnants of structures that had important functions in ancestors Have become smaller over time Ex. snakes pelvis, leg bones Molecular biology closely related species share similar DNA and proteins. A Cline Comparative Anatomy looks at morphology (appearance inside and out): Homologous structures body parts that resemble one another in different species because they have evolved from a common ancestor Example of Descent with Modification Analogous structures body parts that resemble one another in different species because they evolved independently as adaptations to similar environments Cline: a graded change in some trait along a geographic axis 6