Burke ANTH 1210 Winter 2025 Week 4 UMLearn PDF

History of Evolutionary Theory ◼ Pre-Darwinian views ◼ Darwin ◼ Neo-Darwinian thinking  Evaluation Term Test I 25% final grade, material from chapters 1, 2, 3, 4, 5 11 February (**in class**) – 50 multiple choice questions Term Test II 25% final grade, ma...

History of Evolutionary Theory ◼ Pre-Darwinian views ◼ Darwin ◼ Neo-Darwinian thinking  Evaluation Term Test I 25% final grade, material from chapters 1, 2, 3, 4, 5 11 February (**in class**) – 50 multiple choice questions Term Test II 25% final grade, material from chapters 7, 8, 9, 10, 11 25 March (**in class**) – 50 multiple choice questions Final Exam 50% final grade, cumulative – all material (above chapters, plus 6, 12, 13), final examination period (**11-25 April**) – 100 multiple choice questions Evolution Systematic change through time Organisms - Biological change ; Social systems - cultural change Modern life forms originated from other species in the past (versus the idea that each modern species was independently created as they exist in form today) Evolution allows for the idea of change Pre-Darwinian Views of the Natural World Perceptions on VARIATION and CHANGE in the natural world: Essentialism Great Chain of Being Catastrophism & Uniformitarianism Transformational Evolution  Essentialism Traced to Plato Fixed forms exist perfect and unchanging in eternity Differences perceived as ‘accidents’ – does not affect their unchanging essence Elaborated by Aristotle – used similarities and differences to arrange all life in a single line…  Great Chain of Being Framework for interpreting the world All organisms linked in an enormous single line/chain (no gaps, no flexibility, no extinction) Steps: organisms above or below arranged by least possible difference Ranking of organisms … including humans (‘divine ideal’: angels highest, then humans) Believed different human ‘varieties’ could not occupy the same developmental level (e.g., gender, ‘race’, etc.) Reorganized by…  Carolus Linnaeus (1707-1778) Modern biological taxonomy (classification) Carolus Linnaeus Essentialist – number of species created were fixed & unchanging Based on similarities and differences… Did not suggest evolutionary relationships, but did recognize close relationships, e.g., humans, apes, monkeys Controversy: humans depicted as simply part of nature Modern Taxonomy based on Linnaean classification Kingdom (Anamalia) Phylum (Chordata) Class (Mammalia) Order (Primates) Family (Hominidae) Genus (Homo) Species (sapiens) Anatomically modern humans: Homo sapiens sapiens Reproductively Isolated  As the work of ‘exploration’ continues… Georges Cuvier (1769-1832) Pioneer in palaeontology First important excavations of fossils in Seine River Basin – new forms of diversity How to explain?....proposed catastrophism... Catastrophism Fossil species repeatedly wiped out and replaced by new species Concept of “revolutions” Natural disasters (e.g., floods) But... Cuvier never argued that one species emerged out of another Only that new species were created when others were destroyed (intentional) Problem: made creation appear disorderly and arbitrary Charles Lyell 1797-1875 Scottish geologist Stimulated interest in alternate idea, Uniformitarianism, in the 19th century Lyell & Uniformitarianism Natural forces constantly reshaping earth (erosion, deposition) –operated in the past & continued to operate in the present Change in organisms like cyclic changes in seasons and geology (a ‘natural’ phenomenon) Late 19th century – catastrophism falls out of favour, uniformitarianism gains more acceptance Critical concept that shaped Darwin’s ideas Jean Baptiste de Lamarck (1744-1829) Understood the world could change Did not believe that organisms existed fixed & unchanging (essentialism) Explored mechanisms to explain how biological change could occur Lamarck Once a species existed, it could change over time to become more ‘perfectly suited’ to its environment Developed idea of “transformational evolution”: All organisms in a species change physically in response to new environmental demands (i.e., no new species created over time) Lamarck Two ways transformation could occur: Law of use and disuse: features of an organism strengthened / enhanced by use (or weaken / disappear through disuse) Law of inheritance of acquired characteristics: changes occurring in an organism’s lifetime could be passed to offspring Radial Sesamoid Bone Lamarck Noted fossil species resembled living species - suggested they were ancestors, but... Fossils looked different because influenced by different climate/geography Argued: the world could change; the creator provided species with the ability to change with it Lamarck Demonstrated that species could vary over time Others, however, were observing that contemporaneous species could vary over geographical space (Europe, America, Africa, Asia) The Question..... Why…..?????  Charles Darwin Alfred Russel Wallace 1809-1882 1823-1913 5 yrs on H.M.S. Beagle Traveled S. America (4 yrs) (1831-36) “Observing Variation” (species diversity) species emerging through ‘descent with modification’ from a single parental population Darwin On the Origin of Species by Means of Natural Selection or Preservation of Favoured Races in the Struggle for Life Published November 1859 (he was 50) Darwin - Background Lyell – Principles of Geology 1831: geology & uniformitarianism Observed change - artificial selection – breeders & gardeners (Darwin – pigeons) Competition for scarce resources –Malthus – Essay on the Principle of Population – read by Darwin in 1838… Thomas Malthus (1766-1834) English clergyman & political economist Concern: decline of living conditions in 18th century England Conflict (struggle for life): Nature reproduces itself geometrically (2, 4, 8, 16,...) Resources increase arithmetically (1, 2, 3, 4,...) Famine & poverty Darwin’s Contributions... Theory of Natural Selection “Variational Evolution” Biological variation is present in any given population Variants best suited/adapted to current environment have a greater chance of surviving Variants with greater chance of surviving also have greater chance of reproducing offspring Note: For Darwin: Unlike Lamarck… Environmental change did not create variation in the species – for Darwin, variation is already present in the population When environment changes, some variants (which already exist) may ‘have an advantage’ Natural Selection: is not purposeful No genetic understanding (how variation came to exist)  Gregor Mendel (1822-1884) Austrian monk/amateur botanist – pea plants (phenotypes) Contributed to concept of transmission of inheritance (‘genetics’ origins – phenotypes, not genotypes) Pub 1866 After Mendel… Genes = segments of DNA serving as the building blocks of proteins Alleles = alternative forms of a gene at the same locus on homologous chromosomes (23 pairs, 46 chromosomes in total)... Chromosomes A pair of homologous chromosomes. A gene locus (the location of a particular gene on the chromosome) A pair of alleles (alternate forms of a gene at the same locus).  New Genetic Combinations in Offspring New variation is inherent, because of: Sexual Reproduction (2 biological parents contributing alleles) Genes may be shared, but they are not identical  New Genetic Combinations in Offspring Meiosis – produce gametes (ova, sperm) – each possessing 23 chromosomes Gametes = only a sample of parents’ entire genetic makeup GAMETES & potential sibs!  Gametes SPERM OVUM 23 chromosomes 23 chromosomes (from biological + (from biological = 46 chromosomes with conception mother) father)  So… with the principles in place… let’s review the evolutionary forces… Evolutionary Forces: Which genes are Mutation GENETIC present in a population Natural Selection COMPOSITION Gene Flow Random Genetic Drift GENETIC STRUCTURE BIOLOGICAL VARIATION Factors that Produce and Redistribute Variation Mutation Mutation = change in genetic material Basic ‘creative’ force in evolution – only way to produce truly ‘new’ variation Mutations typically rare, with little effect on populations (unless picked up by natural selection)  Factors that Produce and Redistribute Variation Gene Flow Movement of genes/alleles from one population into another – “genetic admixture” (how?) Migration and interbreeding Geographic (e.g., island) and cultural factors (e.g., transportation) can play a role Tends to decrease genetic differences between populations (e.g., alleles present & frequencies) Factors that Produce and Redistribute Variation Random Genetic Drift Has potential to increase differences between populations (e.g., alleles present & frequencies) Genes/alleles become more/less common due to small population size and ‘sampling’ How does ‘sampling’ occur….?  Factors that Produce and Redistribute Variation Founder Effect C C BC Migration C C C C C C C C Founding group & descendents carry only a C C C C small fraction of alleles (and variation) C C VC C Restricts the ‘gene pool’ of the next generation C C C B V C B C C CC  Factors that Produce and Redistribute Variation Bottleneck C C C BC Only a small portion of a C C C C population (and its genes) C C C survives famine, war, plagues C CC C C C C C C B VC V B C C C Natural Selection A slow gradual process: reshapes population allele (gene) frequencies 2 principles: survival (differential mortality) and reproduction (differential fertility) From a lifecourse perspective – it’s about surviving to reproduce (pass genes) and how many offspring produced (increases the likelihood of genes persisting through generational time)  Human Populations: A Life Course Perspective “differential mortality: they survived: Infancy Childhood Adolescence to make it to “reproduction” But did they reproduce…? Human Populations: A Life Course Perspective Their ‘fitness’? Their genetic contribution to the next generation? Natural Selection Mutation, gene flow, genetic drift – may influence what genes are present in a population Natural Selection - provides directional change in gene frequencies (i.e., alleles more/less common due to selection) As environment changes, selection pressures change: different alleles may become more/less adaptive Changes in allele frequencies may lead to biological (genetic) variation Evolutionary Forces: Which genes are present in a Mutation GENETIC population Natural Selection COMPOSITION Gene Flow Random Genetic Drift Mating Practices GENETIC Random (or not) STRUCTURE Mating To understand variation, must Example: see what genes are present & Global A,B,O BIOLOGICAL how assembled VARIATION Frequencies into genotypes  Karl Landsteiner (1868-1943) Austrian physician 1900 – identified the ABO blood group system Model of Mendelian inheritance (alleles at one genetic locus)  Aspects of the ABO system There are 3 alleles in this system (genetic polymorphism): A, B, O There are 6 possible genotypes: AA, AO, BB, BO, AB, OO But only 4 possible phenotypes: A, B, AB, O (O is recessive; A and B are co-dominant)  PUNNETT SQUARE: Genes in Families Biological father GAMETES A B Biological B AB BB mother O AO BO  Genes in Populations: A, B, O Allele Frequencies Global allele frequencies: O (62.5%), A (21.5%), B (16.2%) Of note: Clinal distributions (small variations) Distinct pockets (notably high/low frequencies) How to interpret the global distribution of A, B, and O alleles... Mutation? (genetic polymorphism) Gene Flow? Movement & interbreeding of people (and their genes) (clinal distribution) Random genetic drift? Founder Effect & Bottlenecks likely (notable pockets) How to interpret the global distribution of A, B, and O alleles... Also a case for Natural Selection? (through ‘differential mortality’?) Example & smallpox imagery…  Smallpox Viral disease Droplet transmission (coughs and sneezes) Regular, large scale epidemics; high mortality Lower frequencies of A allele in areas with histories of smallpox  Variation in antigens on the surface of red blood cells  How to interpret the global distribution of A, B, and O alleles... Smallpox virus surface antigens ‘look like’ the antigens on type-A red blood cells Result: no immune response Higher mortality and lower A allele frequencies