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U of A ANTH 1013 - Macroevolution

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ANTH 1013 1st Edition Lecture 7Outline of Last Lecture I. The Evolutionary SynthesisII. How does evolution occur?III. MutationIV. Natural selectionV. Gene flowVI. Genetic drifVII. What if population isn’t evolving?Outline of Current Lecture I. Microevolution vs. MacroevolutionII. What is a species?III. Biological Species ConceptIV. How do new species form?V. MacroevolutionVI. Evolutionary Species ConceptCurrent LectureI. Microevolution vs. Macroevolutioni. Evolution: change in allele frequency over timea. Remember that this means we are considering the gene pool of population, not individualsii. Microevolutiona. A change in a gene pool observed over a period of generationsb. When microevolutionary changes accumulate over larger periods of time wecan observe longer term evolutionary trends and speciation1. These trends are referred to as macroevolutionc. Microevolution and macroevolution are the same thing, just viewed from different perspectivesiii. Descent with modificationa. Darwin’s argument was that all organisms evolve through descent with modification1. Splits from a single species into two descendant species results in branching pattern of relationshipsiv. Mechanisms of evolutiona. MutationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.b. Natural selectionc. Gene flowd. Genetic drif1. These mechanisms apply equally to microevolution and macroevolutionv. How do these mechanisms bring about the branching patterns we see in nature?a. First we have to understand what is meant by species and speciationII. What is a species?i. The basic unit of evolutiona. Population: an identifiable group of individuals of the same speciesb. Subspecies: a collection of populations distinguished by one or more unique featuresc. Species: a group of interbreeding populations that are reproductively isolated from other such groupsd. Goes from individual, population, subspecies, speciesIII. Biological Species Concepti. A group of actually or potentially interbreeding populations that is reproductively isolated from other such groupsa. Emphasizes the ability to reproduce since this is how alleles can be shared within a group of organismsii. How are species reproductively isolated?a. Pre-mating isolating mechanisms1. No attraction2. Physical incompatibility of genitaliab. Post-mating isolation mechanisms1. Sperm egg incompatibility2. Zygote, embryo, or offspring isn’t viable3. Offspring sterilityIV. How do new species form?i. Allopatric speciation a. Allopatric speciation – a large range that is equally fragmented into 2 new populationsb. Splitting of parent species range = vicariance eventc. Geographic barriers lead to the fragmentation of species range – populations become isolated from each otherd. Lack of gene flow leads to divergence, accumulation of reproductive isolating mechanisms, and eventually speciationii. Peripatric speciationa. Geographic barriers lead to the fragmentation of species range – populations become isolatedb. Peripheral isolate is much smaller that the main body of the speciesc. The peripheral diverges from the ancestral state, but the main body does notiii. What if barriers disappear?a. Lack of gene flow leads to divergence, accumulation of reproductive isolating mechanismsb. However, if barriers disappear and speciation is incomplete, the populations will reestablish gene flow and set up a hybrid zone between the formerly geographically distinct populationsV. Macroevolutioni. Macro and microevolution are not different evolutionary mechanismsa. Microevolution: small short term changes over just a few generations (easily observed)b. Macroevolution: larger changes over many generations. The logical extension of microevolutionary processes!1. The two are the same, just viewed from a different scalec. Directional selection: change in average phenotype – direction determined by environmentd. Stabilizing selection: no change in average phenotype – reduction in variance or rangee. Genetic drif: change in average phenotype – direction of change is randomii. Macroevolutionary patternsa. Patterns of macroevolution are largely determined by 2 factors:1. Branching patterns (or lack thereof) of speciationa. Cladogenesis – splitting of lineagesi. The production of more than one daughter species – “branch creation”b. Anagenesis – long term evolutionary change without the splitting of lineagesi. Long term accumulation of lots of change without splitting2. Tempo – the rate of phenotypic change over timea. Darwin hypothesized that change was slow, constant, and gradual (gradualism)b. We now know that this is an oversimplification, sometimes, change is really rapid (punctuated equilibrium)c. Sometimes, the mean phenotype doesn’t change at all (stasis)b. What about fossils?1. The biological species concepts is hard to apply to the fossil record. Could fossils have interbred? We can’t know.a. What makes this concept hard to apply is that this concept doesn’t tell us how different two species should lookVI. Evolutionary Species Concepti. A species is a lineage of ancestral-descendent populations of organisms that maintain its identity from other such lineages and which has its own evolutionary tendencies and historical fatea. This concept is useful in the fossil record because:1. It recognizes that species evolve2. In practice, we identify fossil species based on morphology, not because of a guess about whether or not they could interbreedii. What might the evolutionary species concept tell us about Neanderthals?a. An estimated 2.5% of our DNA is from Neanderthals1. Average European has about 2.7% 2. African descent = very littleiii. Macroevolutionary patterns: tempoa. Gradualism – slow continuous change over time. May or may not be accompanied by cladogenetic eventsb. Punctuated equilibrium – long periods of stasis (or slight gradualism) interspersed with periods of rapid change. Typically linked to cladogenetic events1. Gradualistic evolution in hominin brain sizea. Human brains hit their modern size about 200,000 years ago, however, the size began to increase about 3.5 million years ago iv. Extinction happensa. Extinction can be caused by environmental change (either gradual or sudden) and/or by competition with other


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