Chapter 17 Processes of Evolution Early Beliefs 19 th century discovered species shared many traits but lived in different parts of the world Problematic species only looked similar on the outside but inside were very different ID: 998926
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1. Unit 6: EvolutionChapter 16: Evidence of EvolutionChapter 17: Processes of Evolution
2. Early Beliefs19th century: discovered species shared many traits, but lived in different parts of the worldProblematic – species only looked similar on the outside, but inside were very different Fossils were also puzzling because deeper layers held fossils of simple marine life and layers above held similar but more complex fossils
3. New Ideas19th century naturalists tried to explain evidence that life on Earth had changed over timeJean-Baptiste Lamarck was the first to think about lineage, or a line of descentBelieved a species gradually improved over generations due to a drive toward perfectionProposed that environmental pressures cause an internal need for change and the resulting change is inherited by offspringhttps://www.youtube.com/watch?v=nWHorwSSpfo
4. “In 1880 he cut off the tails of 20 successive generations of mice and showed that not a single tailless mouse was born.” --Weissman
5. Charles DarwinNaturalist on the H.M.S. Beagle in 1831Circumnavigated the globe over five years making detailed observations of geology, fossils, plants, and animalsHe observed how well suited many organisms were to their environment
6. Charles DarwinBeagle stops at the Galápagos Islands – 500 miles off the coast of EcuadorThough close together, each had a unique climate and organisms Darwin thought that if humans could change a species through artificial selection [selective breeding], then perhaps the same process could happen in natureDarwin’s Question – did animals on the islands once come from the same species, then change?
7. Charles DarwinFor example, each island had a species of finch adapted to its climateDarwin concluded the different finch beaks were inherited variations (changes) that helped the birds compete for food, survive, and reproduce
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9. Evolution In 1859 he published On the Origin of Species by Means of Natural Selection suggesting species evolve and all descend from a common ancestorEach species has its own unique set of heritable (genetic) differences from the common ancestor, which have accumulated gradually over very long time periodsEvolution: The changes that occur over time in the hereditary features of a species.
10. Natural SelectionDarwin’s suggested mechanism of evolution was natural selection Natural Selection: process by which heritable traits that help organisms survive and reproduce become more common in a population over time.Explanation of how evolution works, NOT a synonym
11. Natural SelectionAdaptation: heritable trait shaped by natural selection, increases fitnessThe better adapted an organism is, the higher its chances of survival areFitness: measure of how much a trait contributes to the next generationIf necessary to survival, it will be passed on – Survival of the Fittest [not about strength]Faster predator – more food, survives longerCamouflaged prey – better protection, survives longerhttps://www.youtube.com/watch?v=JUM6NOARlO4
12. Natural SelectionBased on 4 observations in nature:Members of a population often vary greatly in their traitsTraits are inherited from parent to offspringAll species are capable of producing more offspring than can be supported by the environmentMany of the offspring do not survive because of lack of resources
13. Natural SelectionFrom his four observations, Darwin made two inferences to explain natural selection:Individuals with more favorable traits have a higher probability of surviving and reproducing This unequal ability to survive and reproduce leads to an accumulation of favorable traits in the population over timeGiven enough time, natural selection modifies a population and produces a new speciesNatural selection is ALWAYS HAPPENING! The environment is always changing and therefore so do the factors that determine success
14. Evidence for Evolution1. Fossils: remains of once-living things from the pastThe fossil record shows that ancient species share similarities with species that live on Earth now Some have changed, and some haven’t at all
15. Evidence for EvolutionFossils are relatively rare, so the fossil record will always be incompleteFossil records holds clues to evolution:Ancestors of whales probably walked on landThe skull and lower jaw have characteristics similar to those of ancient carnivorous land animalsDerived Traits: newly evolved traits (feathers) that do not appear in the fossils of common ancestorsAncestral Traits: primitive features (teeth) that appear in ancestral forms
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17. Evidence for Evolution2. Comparative Anatomy [Morphology]: study of similarities and differences in the anatomy of different species.Homologous Structures: Body parts from different groups that appear similar because they evolved from a common ancestor; same genes, different purposesVestigial Structures: Type of homologous structure that has reduced function or no function in some organisms
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19. Evidence for EvolutionAnalogous structures: Body parts that look alike in different groups, but evolved independently, not from a common ancestor
20. Evidence for Evolution3. Comparative Embryology: Similar patterns of embryonic development reflect shared ancestryEmbryos show homologous structures during development, these develop into completely different structures laterStructure that develops into fish gills is what develops into ears, jaws, and throats in reptiles, birds, and mammals
21. Evidence for EvolutionMaster genes control embryonic development patternsThese have changed very little or not at all over evolutionary timeMaster genes with similar sequence and function in different lineages are strong evidence that those lineages are related
22. Evidence for Evolution4. Comparative Biochemistry: species with a common ancestor share certain amino acid sequences, the more closely related, the greater number of shared sequencesSimilar genes give rise to similar proteins
23. Figure it OutWhich species listed would be most closely related to the honeycreepers?
24. AdaptationsCamouflage: Adaptations that allow organisms to blend in with their surroundingsBecome almost invisible to predators and preyVaries by species, but their environment is often the most important factor in how they appearMimicry: One species evolving to resemble another species
25. CamouflageMimcry
26. AdaptationsAntimicrobial Resistance: when bacteria develop drug resistanceAn unintended consequence of antibiotic development
27. Bloody Hippo SweatContains no blood or sweat, keeps their skin moist and protects it from sunburns, as well as many infections.White-tailed Deer Fake DeathWhen a predator approaches, heart rate is programmed to drop so low that they enter a state of tonic immobility, coupled with involuntary peeing and pooping
28. Exploding Malaysian Ant When the ant senses its life is at risk, it will often click its own self-destruct button and explodeNorthern Fulmar Projectile Vomit A tiny confrontation and a chick throws up chunks of orange puke that is so nasty and sticky, it becomes the foulest prey of all time
29. Population GeneticsNatural selection is not the only way to explain how evolution worksStudies from population genetics have led to some evolutionary theory that focuses on genesGene Pool: All the available genetic information (alleles) within a population
30. Population GeneticsVariations within a population arise from different alleles of shared genesSources of variation include mutation, crossing over independent assortment, and fertilizationAllele Frequency: how frequently an allele shows up in a population
31. Population GeneticsGodfrey Hardy and Wilhelm Weinberg showed, mathematically, that evolution won’t occur unless allele frequencies in the population are acted upon by forces that cause changeHardy-Weinberg Principle: when allele frequencies in a population remain constant, a population is in genetic equilibrium [NOT CHANGING]
32. Population GeneticsHypothetical, non-evolving population that preserves allele frequenciesFor example – consider a gene that codes for feather color in owls, [R] is red, [Rr] is speckled, [r] is greyFirst generation of owls in a population has 1 red, 4 speckled, and 2 grey owlsIn the next generation, there are 3 red, 12 speckled, and 6 grey owlsEven though the population has tripled, the ratio of red to speckled to grey owls remained the same – allele frequencies are unchangedNatural populations are rarely in H-W equilibrium, but the model measures if forces are acting on the population
33. Hardy-WeinbergAccording to H-W, 5 conditions must be met for a population to have NO EVOLUTION (genetic equilibrium)No migration, Large populations, No mutation, Random mating, No selectionThese are the mechanisms of evolution – IF they ARE happening, evolution is happening, H-W is null and void
34. Hardy-Weinberg1. No MigrationA population in genetic equilibrium experiences no gene flow – no new genes enter the population and no genes leave (emigration and immigration)Migration increases genetic variation within a population and reduces differences between populations
35. Hardy-Weinberg2. Large PopulationGenetic Drift: Change in the allele frequency due to chanceAnt is stepped on, rabbit swept up by a tornado, plane crash killing a Nobel Laureate.In large populations, enough alleles “drift” to ensure the frequency of alleles remains relatively constantFounder Effect and Bottleneck are both examples of genetic drift
36. Hardy-WeinbergFounder Effect: When a small sample of a population settles in a location separated from the rest of the populationAlleles that were uncommon in the original population may be common in the new population (recessives may start showing up more frequently)
37. Hardy-WeinbergBottleneck Effect: When a population declines to a very low number and then reboundsGene pool of rebound population is very similar to the population at its lowest level – reduced diversityAfrican cheetahs have experienced this twice in the last 10,000 years, they are now so genetically similar they appear inbred
38. Hardy-Weinberg3. Random MatingIn random mating, all individuals are considered potential partners – ensures that there is a vast range of genetic makeup in a population and that the same allele is not constantly being expressed.If mating is not random, homozygous alleles will become more frequent
39. Hardy-Weinberg4. No MutationMutations can change allelic frequencies in a populationSome have no effect, some are harmful, some may lead to an advantageIf there are no mutations, phenotypes will not changeMutations serve as the basis for natural selection!
40. Hardy-Weinberg5. No Natural SelectionH-W requires that all individuals in a population be equally adapted to their environment and contribute equally to the next generationNatural selection alters phenotypes in 3 waysStabilizing selection, directional selection, disruptive selection
41. Hardy-WeinbergStabilizing Selection: most common form of natural selection, eliminates extreme expressions of a trait if the average expression leads to higher fitnessHuman babies that are over or under normal birth weight have a lower chance of survivalDirectional Selection: increases the expression of the extreme versions of a trait (if it makes the organism more fit)Peppered moth became a darker color during industrial revolution – they better matched the sooty environment
42. Hardy-Weinberg Disruptive Selection: splits a population in two groups – removes individuals with average traits, retains extreme traits at both ends of the continuumNorthern water snakes – mainland snakes have mottled skin, those on rocky shore have gray skin, intermediate coloring would be more visible to predatorsAlso sexual selection – a change in frequency of a trait is based on the ability to attract a matePeacock tail – though it is large and cumbersome and may attract predators, it enhances reproductive success
43. Hardy-Weinberg
44. SpeciationEvolutionary mechanisms do not always contribute to the origin of a new speciesSpecies: group of organisms that can interbreed and produce fertile offspringSpeciation: process in which some members of a sexually reproducing population change so much they can no longer produce fertile offspring with members of the original population
45. SpeciationFor speciation to occur, populations must split (diverge) and become reproductively isolatedOnce separated, evolution happens in each group, but differentlyThey gradually become different because their environments are different, and in time each group may become a different species.As a result – they would not be able to produce fertile offspring if brought back together
46. SpeciationAllopatric Speciation: A physical barrier divides one population into two or more populations.Ocean, river, mountain, glacier, lava, etc.Abert squirrelKaibab squirrel
47. SpeciationSympatric Speciation: Species evolves into a new species without a physical barrier.Apple maggot flies – split based on the fruit they eatMany plant species – a mutation in one species increases the number of chromosomes (polyploidy) and they can no longer reproduce with the original species
48. SpeciationOnce species are reproductively isolated, gene flow is prevented through the following mechanismsPrezygotic Isolating Mechanism: prevents reproduction by making fertilization unlikely – prevents genotypes from entering the gene pool through geographic, ecological, behavioral, and other differencesEastern and Western meadowlarks – similar in appearance and geographical ranges, but, use different mating songs and therefore do not interbreed
49. SpeciationPostzygotic Isolation Mechanisms: fertilization occurs, but the hybrid offspring cannot develop or reproduce – prevents the offspring’s survival or reproductionLIGERS!
50. Patterns of EvolutionEvidence of speciation is visible in the patterns of evolutionAdaptive Radiation (divergent evolution): one species gives rise to many in response to a new habitatHappens in a relatively short time, often follows large scale extinctions
51. Patterns of EvolutionConvergent Evolution: Unrelated species evolve similar traits because they live in similar climates, in different parts of the world.
52. Patterns of EvolutionCoevolution: Relationship between two species is so close that evolution of one affects the evolution of the other Adaptations and counter-adaptations
53. Patterns of EvolutionRate of speciation may happen rapidly, or over a course of millions of yearsGradualism: theory that evolution proceeds in small, gradual stepsPunctuated Equilibrium: theory that rapid spurts of genetic change cause species to diverge quickly
54. Modern ClassificationREFRESHER! Be familiar with how to name speciesGenus: a group of species that share a unique set of traitsSpecies: unique type of organismTogether, these designate the species name – Homo sapienAlways italicized, genus is always capitalized
55. Modern ClassificationCompare a domestic cat with a lionThey are in the same Kingdom, Phylum, Class, Order, and Family but they ARE DIFFERENT in the Genus and species groupingsBUT - A lion shares kingdom, phylum, class, order, family, AND Genus with tigers, leopards, and jaguarsThey are different species, but a lion is more closely related to tigers, leopards and jaguars than it is to a house cat
56. Modern ClassificationPhylogeny: evolutionary history of a speciesMolecular Clock: a model used to compare DNA sequences from two different species to estimate how long the species have been evolving since they diverged (split) from a common ancestorScientists use these to compare the DNA sequences of genes shared by different species – difference between the sequences indicate mutations in the species
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58. CladisticsCladistics: classifies organisms according to the order they diverged from a common ancestorAncestral Character: inherited trait or feature that is found in the entire line of descent of a group of organismsA backboneDerived Character: inherited trait shared by a group of organisms, but not present in the ancestral groupFeathers
59. CladisticsDerived characteristics can be used to construct a cladogramCladogram: a branching diagram that represents the proposed phylogeny (evolutionary history) of a species or groupThese are similar to pedigrees – the branches of pedigrees represent ancestry, the branches of cladograms represent evolutionary history
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