Lecture 1Micro vs macro evolution: Opposing views state that macroevolution is simply an extension ofmicroevolutionary processes that persist for a long time and can explain macroevolutionarypatternsErnst Mayr: Darwin’s Theory of Evolution1. Evolution as sucha. The world is not constant or recently created nor perpetually cycling (nottopological)b. The world is steadily changing, and organisms are transformed in time (Lyell’sgeological influence)2. Common descent: every group of organisms descended from a common ancestor, soALL living organisms share a common ancestor, a pattern3. Multiplication of species: species multiply (speciation), speciation explains the origin ofdiversity, usually occurs due to some form of geographic isolation and many generationsof separated reproduction leading to different populations, a mechanism4. Gradualisma. Evolution occurs by gradual change of populations (Lyell’s influence), not bysudden (saltational) production of new individuals that represent a new type5. Natural selectiona. Individuals within species varyb. Some variations are passed to offspringc. More offspring are produced than can survive (Malthus’ influence)d. Survival and reproduction is not random. Individuals that have favorablevariations often survive to reproduce or reproduce moreGould’s Darwinism focused on gradualism and natural selection- Gradualism: darwin did not claim the evolutionary changes are slow and continuous, butthat they do not evolve through saltational changes, but by a series of intermediate stepsin successive generations- Natural selection: darwin claimed that natural selection explains only adaptive traits, notall traits, for instance, other mechanisms like genetic drift and gene flow promote changeGould said modern evolution is Darwinism and1. Agency: (Does natural selection only occur on organisms?)a. Darwin thought NS acts at organismal and population level, but it can also act onother levels, genes, cells, groups, species2. Efficacy: (Is natural selection the major director of evolution?)a. Constraints that channel evolution: developmental and structural changes3. Scope: (Does micro- extend evenly to macro-evolution?)a. Other process such as mass extinctions have no presence within the theory ofNS but still impact evolution dramatically, species selectionWhat is macroevolution?- Taxonomic: evolution above the species level, between species- Integrative: evolution of traits that distinguish major groups- My definition: study of processes that split biological lineages and the historical patternsthat result3 schools of Darwinism1. Neo Darwinism: Darwinism without an inheritance of acquired characters, recognizedimportance of mutations and variations within a population2. Early population genetics, a strongly reductionist school that defined evolution as themodification of gene frequencies by natural selection; and3. Modern evolutionary synthesis, which continued the traditions of Darwin and thenaturalists while accepting the findings of genetics.Lecture 2Modern Synthesis is a combination of genetics with Darwin’s evolution theories, mainly focusedon microevolutionModern theory differs from Darwinism:1. It recognizes several mechanisms of evolution in addition to natural selection, such aschanges in gene frequency brought by random genetic drift and gene flow2. It recognizes that characteristics are inherited as discrete entities called genes. Variationwithin a population is due to the presence of multiple alleles of a gene. Genetic variationarises by random mutations and recombination3. It postulates that speciation is (usually) due to the gradual accumulation of small geneticchanges. Macroevolution is the sum of microevolution.a. Adaptive genetic variants have individually slight phenotypic effects so thatphenotypic changes are gradualb. Diversification comes about speciation, which usually involves a reproductiveisolation mechanism among populationsc. These changes over a long period of time will warrant the designation of highertaxa levels4. Darwinism concerned with organisms, speciation, and individuals, while modernsynthesis works at the level of genetics, phenotypes, and populationsHW as a null model for microevolution, assumes that no evolution is occurringDeviation from the HW is when one of the assumptions is not met: NS, GF, GD4 Postulates of NS:1. Populations harbor variation: measure individuals, variation in beak depth2. Heritable traits: observe correlations between parent and offspring3. Not all individuals survive to reproduce: identify individuals by banding4. Survival is non random with respect to traits: observe population size and seedabundance, tested the survival of a subset of finches before and after droughtCommon Misunderstandings of Natural Selection1. Selection acts on individuals, consequences occur in populationsa. Selection acts to weed out those that don’t surviveb. i.e. during drought finches with smaller beaks could not eat and were dying,those with larger beaks survived and had more offspring with larger beaks, afterdrought there were more finches with larger beaks, changing the populationfrequency2. Selection acts on phenotypes but microevolution is change in gene frequenciesa. Genetic basis for how beaks vary in size, changes in genetic frequencies lead toa change in phenotype3. Natural selection is not forward lookinga. Random mutations lead to variation and selection will weed out those that don’tsurviveb. NS cannot produce features on the ground that they will become beneficial sometime in the futurec. Adaptations are based on conditions experienced by generations in the past4. Natural selection mainly acts on existing traits, traits gradually change or develop overtime5. Natural selection is not random with respect to fitnessa. Select phenotypes with higher fitnessConceptCorrectIncorrectExisting Variation AmongIndividualsCommon and important forevolutionary changeRare and/or unimportant.Deviation from “essence” or“type” of the species.Origin of new traitsArise in an undirected fashionby random mutation. Somedetrimental, some neutral,some beneficial. Sortedaccording to effects onorganismal reproduction afterthey ariseArise in response to need.Always beneficial. Offspringmay exhibit new beneficialtraits even if the parents didnot possess them. The typesof new traits that occur aredetermined based on theenvironmentInheritanceTraits are inherited fromparents regardless of whetherthey are beneficial