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This document contains a list and explanation of various sources of evidence for common ancestry. It explores evolution as a population-level phenomenon with examples. It also summarises the concept of natural selection and the explanation of its improvement of organismal adaptiveness.
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Diverse living species show common ancestry [evidence of CA] . 1 List and explain four sources of evidence for common ancestry - Common ancestryis the idea of tracing back lineagesof living species far back enough, those species share acommon ancestors...
Diverse living species show common ancestry [evidence of CA] . 1 List and explain four sources of evidence for common ancestry - Common ancestryis the idea of tracing back lineagesof living species far back enough, those species share acommon ancestors - The biogeographicpattern of similar speciesclusteredin geographical areas - Homologiesare structures that havedeep similaritiesbetween species - Studies offossilsshow that some fossils share identicalcharacteristics - Transitional fossilsthat have some not all of thederived traits of a living group - Nested structures of taxonomic groups, beginning froman ancestor and radiating like thebranches from a tree,within groups (withoutoverlaps) - Separate ancestry is incorrect 2. xplain why evidence of common ancestry means that evolution must have occurred E - accumulatingdifferencessince they last shared thatancestor. Therefore,evolution must have occurred to explain these differences. volution is a population-level phenomenon [population level] E . 1 Associate evolution with changes in frequency in a population (not changes in individuals) - Evolutionis the change in thefrequency of geneticvariants in a population over generations Continuing until one variant isfixed, meaning thatall other variants become extinct - It is not about individuals changing, but about thepopulation-levelchange ingenetic composition. - Evolution only happens when a population has genetic variation - Population of white flowers, if one flower produces a purple flower offspring due to genetic Mutation, you now have a population of purple flowers (genetic variation) - Polymorphicpopulation, change in the frequency ofthe variants, multiple variants within a population - Variants in traits exist, and evolution will continue to act on populations - Evolution does not require selection Natural selection explains adaptation [selection concept] . 1 Explain why natural selection tends to improve organismal adaptiveness - Natural selectionfavorsgenetic variantsthatenhance/increasesfitnessto go to fixation and variants that reduce fitness to be loss from the population - Increase frequencyin populations over time - Natural selection can occur onmultiple alleles - Natural selection is non-random - Populations over time are not random but are adaptive because of natural selection - natural selection, by definition, favors traits thatincrease fitness(i.e., enhance survival or reproduction). Traits that actively reduce fitness would not be favored by natural selection - natural selection does not guarantee that all traits arecurrently beneficial - Traits that evolved by natural selection may no longer be beneficial becauseenvironments change over time. What was once adaptive in a previousenvironment may become neutral or even maladaptive when the environment shifts. he history of common ancestry is depicted in phylogenetic tree diagrams T 1. Identify the different parts of a phylogenetic tree (clade, root, node, branch, sister taxa) - A branching diagram is aphylogenetic tree - Remove tips or clades from a tree without changing the topology is calledpruning - The point(base) of the treewhere time enters thedeepest ancestry of the the group is called theroot - The bulk of the tree is composed ofbranches, someare internal some are external The lines on the diagram, which representpopulationlineages - Where apopulation lineage splitsinto two,nodesof a tree, representslineage splitting - Last common ancestor of the clade marked by the node - When the descendant lineages first became genetically isolated - A grouping of branches and tips that includesalldescendantsof a single ancestral lineage Is aclade - A named group of biological organisms often shown at thetipsof the tree calledtaxa - Sister taxa: Two taxathat share an immediatecommonancestorand represent the most closely related lineages in a tree. 2. Explain how geographic isolation can result in lineage splitting and associate this phenomenon with nodes in a phylogenetic tree. - Lineage splitting;The continuous population thatgets split into two - subpopulationsby climate change or geological - Large population on one land mass and a rare event, if the new landmass is Far away then the new population can immediately be genetically isolated from the first allowing it To evolve independently - Split population at a node - Geographic isolationallows populations to accumulatedifferences over time until they come To be different in visible ways - Two populations that end up separated from one another so they stop exchanging genes - Geographic isolationcan fragment acontinuous populationinto separate subpopulations that no longer exchange genes, leading toindependentevolution. 3. List the clades present in a phylogenetic tree and use this to determine if two trees have 4. the same Topology - Clade can be removed from the root with a single cut - All members of a clade share a more recent ancestor than they share with any lineage outside The clade - A list of all the clades that a tree contains is atree topology elatedness is equivalent to recency of common ancestry R 1.Determine the relative degree of evolutionary relationshipfrom phylogenetic trees of various types - the degree ofrelatednessis determined by therecency of the common ancestor. - Taxathat share amore recent common ancestoraremore closely relatedthan taxa that share a common ancestor further back in time. - - All taxa in a clade are more closely related to one another than they are to any taxon outside Of the clade - Members of a clade are equally related to any species outside of that clade - The same tree topology has the same clades, but different clades are not the same tree topology volution is a branching process that is not goal directed or able to plan ahead E [non - progressive evolution] . 1 Explain why evolutionary advancement is not a meaningful concept. - Evolutionary advancementis not meaningful becauseevolutionis notgoal-directedor aimed at producin to fit their respective environments. 2. Describe the evolutionary history of a clade of interestin non-progressive terms. - The ability to use the metaphor of a phylogenetic tree to convey accurate Evolutionary information istree thinking - Theevolutionary historyof a clade can be describedas aseries of branching eventsthat led todiverse lineages,all of which have adaptedto different environments. No lineage is inherentlyhigher or more advancedthan others,asevolutionis abranching process influenced bychance eventsandnatural selection,without any direction or goal he traits of organisms are a summation of changes along their ancestral lineage T [summation of traits] 1. List the expected characteristic of tips based on changes mapped onto a tree - Thetipsof a phylogenetic tree represent thelivingspecies, and their characteristics are summations of changesthat have occurred along theirrespectivelineages 2. Correctly associate trait changes with internodes (not nodes) hetrait changeshappen along theinternodes(branches)and not at thenodes. T Thenodesrepresent the splitting of lineages, notthe specific trait changes. iological taxonomy is based on phylogenetic relatedness B [clade taxonomy] 1. Identify clades, and only clades, as worthy of formal names - Cladesare groups of species that include a commonancestor and all its descendants. Onlycladesare worthy of formal names because theyreflect true evolutionary relationships. In Figure3-3, groups like(land plants, red algae)form acladeand therefore can be given a formaltaxonomic name. In contrast,(archaea, bacteria)alone is not a clade because it does not include all descendants of their common ancestor. 2. Explain why tree like relationships yield a nested hierarchical taxonomy so long as the taxonomy is based on traits that only evolved once and are never lost - Anested hierarchical taxonomyresults fromtraitsthat evolve once and are never lost, reflecting thetree-like branchingof evolution.. Phylogenetic trees provide information about evolutionary history, including trait homology [trait evolution and homology] 1. Determine the most parsimonious history (or histories) of character state changes for a binary trait on a given tree. Themost-parsimonious historyis the one that requiresthefewest evolutionary changes. 2. Determine whether a character state in two taxa is homologous, given a mapping of trait changes on a tree - The character stateis homologous if it arose froma single evolutionary eventand is passed down through common ancestry. In Figure3-6, thenectar spurin bothcircled flowersishomologous because it evolved in the common ancestor of both species and was retained in all descendants. In contrast, in Figure3-7, the spurs arenot homologousbecause they evolvedindependently in each lineage (i.e.,convergent evolution). volution is a change in the frequency of genetic variation in a population[ evolution definition] E 1. Explain how heritable variation arises from allelic variation in a population - Natural selection is heritable variation in fitness in a natural population - Evolution can occur when there isheritable geneticvariationthat affects a trait - Differences in the versions of alleles present within individuals that are passed on in generations - Heritable variationarises due todifferences in allelespresent at a locus in a population. For example, theA1andA2alleles in themoss populationresult indifferent leaf colors, which contribute toheritable differences. Allelicvariation atmany locican affectcontinuous traitslike height or weight, resulting in abell-shapeddistributionof the trait in the population . 2 istinguish examples of evolution from other kinds of change, such as plasticity D - Plasticity is short term, individuals, not inherited - Evolutionrefers to changes in thefrequency of allelesin a population over generations, whileplasticityrefers tophenotypic changesthatresult solely from environmental influences without altering genetic material. For instance, increasing the height ofvioletswithfertilizerisnot evolution butplasticity. However, theincreased frequency of tuskless elephantsin Uganda due to poachingis an example ofevolutionbynatural selection. - Fitness of homozygotes and heterozygous, allele frequency, population size all alter the probability that an allele goes to fixation volution entails a change in allele frequency [allele frequency] E 1. Interpret a frequency through a time plot applying the terms evolution, fixation, extinction, and polymorphic/polymorphism. - Genotype- genetic makeup - Phenotype- measurable attributes, physical and behavioral - Fixation- occurs when an allele’s frequency reaches1.0 (or 100%) - Polymorphismrefers to the presence of two or morealleles at a locus within a population. - A population is said to bepolymorphicif there ismore than one allelewith a frequency Are present - Extinction- the loss of an allele from a population, which happens when its frequency drops to 0 . 2 Be able to calculate the frequency of an allele given the frequency of genotypes. 3. - Frequency of alleleA: p=2𝑁𝐴𝐴 + 𝑁𝐴𝑎/2𝑁 𝑡𝑜𝑡𝑎𝑙 1-q = p Frequency of allelea(q): 2Naa + NAa / 2Ntotal 1-p = q xample; 30% are A1A1, 20% are A1A2, and 50% are A2A2, the frequency of A1 E is 0.3 + (0.2/2) = 0.4 Allele frequency and genotype frequency can be related by the Hardy- Weinberg law [Hardy Weinberg] 1. Use the Hardy-Weinberg law to calculate expected genotype frequencies given random mating - p+q=1 - p2 forAA/A1A1 - 2pq for Aa/A1A2 - q2 for aa/A2A2 itness is the expected reproductive output of a genotype relative to other genotypes [relative fitness] F 1. Associate fitness with an interaction between a genotype and an environment. - Fitness is determined by the interaction between an organism's genotype and its environment. The reproductive success of a genotype depends on how well it matches the conditions of its environment. For example, the melanistic form of the peppered moth had higher fitness in a polluted environment where dark tree trunks provided better camouflage, but the wild-type moth had higher fitness in a lichen-rich environment. 2. Calculate relative fitness for genotypes given data on reproductive output. -Relative fitness is calculated by dividing the reproductive output of each genotype by the reproductive output of the genotype with the highest reproductive success. For example, if the reproductive output of the melanistic moth in a sooty environment is 100 and that of the wild-type moth is 43, the relative fitness of the melanistic moth is1.0and the relative fitness ofthe wild-type moth is0.43. irectional selection tends to increase the frequency of high-fitness alleles until they become fixed D [directional selection] 1. Predict allele frequency change by directional selection given information on genotype fitness. - Directional selection will cause the frequency of an allele with higher relative fitness to increase over time. 2. Explain why directional selection removes geneticvariationfrom populations. irectional selection favors certain alleles that provide a fitness advantage, leading these alleles D to become fixed while disfavored alleles are lost. This reduces the overall genetic variation in a population as the advantageous allele reaches a frequency of1and other alleles go extinct. - 3. Explain the role of directional selection in keeping genetic diseases at low frequency. Genetic diseases are often kept atlow frequenciesin populations because directional selection acts against alleles thatreducefitness. When an allele causes a deleterious phenotype, selection tends to reduce its frequency, limiting the spread of genetic disorders in the population. . 4 Predict the direction of phenotypic change by directionalselection acting on a continuously varying trait Directional selection will shift the mean value of a trait in the direction ofhigher fitness. For example, if taller giraffes have higher fitness due to their ability to reach more food, directional selection will lead to an increase in the average height of giraffes over generations. utation is the ultimate source of all genetic variation [mutation] M 1. Give examples of mutation at the molecular level. a nucleotide substitution changes one base for another in a DNA sequence, potentially altering the function of the genes . 2 Explain why deleterious and neutral mutations are usually more common than beneficial ones. Mutations increase allelic diversity in a population (genetic variation) Deleterious and neutral mutationsare more commonthan beneficial ones because most mutations disrupt existing functional systemsof a gene (negative effects) beneficial mutations that improve function are rare and typically require precise changes. . 3 Explain why the rate at which mutation generates a trait is independent of whether that trait would be favorable Mutations can generate new allele whose frequency can then be change by natural selection Mutations areindependentof the fitness of the resultingallele Mutations occurrandomlyandindependent of whetherthe trait is favorableor not. Theenvironment does not influence the mutation rate,meaning that beneficial mutations ariseby chance Most trait variation in natural populations is due to variation at many loci, interacting with Environmental variation most variation results from an interaction between allelic variation at many loci (each allele having a small affect) and additional variation due to the environment. Genetic drift - An allele canincrease in frequency even if it doesnot increase fitness (lowers fitness) - An allele’s frequency canfluctuate over time - An allele can belost from a populationeven if itdoesnot have lower fitness - Fewer alleles per locusin a small populations - Changes in allele frequency (evolution) occurs even without selection Directional selection - In small populations, chance fluctuations in allele frequencies tend to be larger and more commo - Larger populations take forever to become fixed or extinct, jags are less dramatic - Directional selection tends to remove genetic variation from the population by driving polymorphic alleles to fixation/extinction. - Explains why organisms tend to be well adapted to their way of life - Requires the genotypes differ in relative fitness - Non random process - Only act on loci that have at least two alleles segregating in the populations - A lower population size increases the rate at which one allele goes to fixation - (and all other alleles go extinct) - Smaller populations take quicker to become fixed or extinct, jags are more dramatic - Beneficial alleles will be lost - Genetic drift can cause the fixation of deleterious alleles - Lose so much variation that all individuals become susceptible to the same disease Life originated 4.5 Ga ago What resulted from the evolution of cyanobacteria? - An ozone (O3) layer built up, making the invasionof land easier - High oxygen levels allowed the evolution of large, multicellular organisms with aerobic respiration (e.g., animals) - The chemical environment of Earth changed, plausibly making it harder for life to originate again .1.2. Associate smaller and larger populations with more or less pronounced genetic 6 drift, respectively. In smaller populations, genetic drift has a more pronounced effectbecause random sampling events can cause greater fluctuations in allele frequencies. In contrast, larger populations are less affected by genetic drift, as their larger gene pool dampens the impact of random fluctuations. .1. Changes in allele frequency, that is, evolution occur even without selection [genetic 6 drift] .1.1. Explain why fluctuations in allele frequency between generations are expected in 6 finite populations, even when alleles are neutral. In finite populations, allele frequencies fluctuate from one generation to the next due to chance events, such as random mating, random survival, or random fertilization. These fluctuations are expected because genetic drift, which is essentially the effect of ampling error in finite populations, impacts allele frequencies even when alleles have s equal fitness. .1.3. Describe the role of genetic drift in removing genetic variation from populations, 6 especially small populations, and why this is a concern for conservation biologists. G enetic drift removes genetic variationfrom populationsby randomly leading to the fixation of some alleles and the extinction of others. This is particularly concerning in small populations, where genetic variation is lost more quickly,resulting in reduced genetic diversity, which makes populations morevulnerableto diseases and environmental changes.Conservation biologists worryabout this loss of genetic variation because it can lead toinbreeding and reducedadaptability, increasing the risk of extinction. 6.2. Genetic drift can reduce the efficacy of natural selection [genetic drift vs. selection] .2.1. Identify genetic drift and small population size as the cause of trajectories in which 6 beneficial alleles go extinct or deleterious alleles are fixed. In small populations, genetic drift can overpower natural selection,causing beneficial alleles to be lost and deleterious alleles to become fixed, simply due to chance. This occurs because the impact of random events on allele frequencies is stronger in small populations, reducing the ability of selection to act effectively. .2.2. Describe the role of genetic drift in lowering fitness and increasing the risk of 6 population extinction. G enetic drift can lead tothe fixation of deleteriousalleles, resulting in adecline in the overall fitness of the population. Thisreductionin fitnesscan lead to decreased fertility, survival, and adaptability, increasing the risk of population extinction,especially in small populations. daptive radiation is associated with periods of species accumulation and diversification A [adaptive radiation] 1. Define adaptive radiation and associate it with the occupation of a new adaptive Zone - Adaptive radation occurs when a lineage undergoes a major transition that allows it to access Some ecological space that was previously inaccessible - Trainsiting to a new adaptive zone is rare because stabilzing selection will generally maintain Adaptions to the current adaptive zone, decrease fitness - The evolution of traits needed for a lineage to function in a dramatically new ecological niche (or "adaptive zone"):The traitsprobably evolved for a function in the current adaptive zone but could later be coopted for the necessary function in the new adaptive zone 2. List examples of adaptive radiations, including eukaryotes and bilaterian animals any phyla of bilaterian animals underwent an adaptive radiation in the early Cambrian M era (540- 485 Ma) 3. Distinguish bilaterians, sponges, and cnidarians and provide examples of the former - Sponges area morphous without obvious symmetry, filter feeders and contain two Tissue layers - Cnidarians have three tissue layers, muscles, nerves, and radial symmetry - Bilaterians also have three tissue layers, muscles, nerves, bilateral symmetry 4. Explain the role of rising atmospheric oxygen and an evolutionary arms race in explaining the explosion of bilaterian diversity in the Cambrian fossil record Multiple bilaterians invade land and a few lineages later reinvaded water. 5. List at least three independent invasions of land - Plants - Insects (arthropods), mililpedes , centipedes, spiders and scorpions - tetrapod here are three domains of life, united by common ancestry [universal common T ancestry] Identify bacteria and archaea as the two prokaryotic domains and summarize their ecological roles B acteriaare metabolically diverse, cycling elementssuch as nitrogen, sulfur, and phosphorus, and include organisms capable of photosynthesis and chemosynthesis. They can form mutualistic relationships (e.g., gut microbiota) or be pathogens. Archaeainclude Euryarchaea and TACK groups, knownfor thriving in extreme environments and having unique membrane lipids. They are metabolically diverse and include mutualists but rarely pathogens. List evidence in support of universal common ancestry C ells: All cells have a lipid membrane, even thoughdifferent materials like oil droplets could have served as the boundary. Metabolism: All cells share similar biochemical pathways,despite the potential for different routes to make the same compounds. D NA and RNA: All cells use DNA and RNA with right-handed sugars and the same four nucleotides, despite the possible diversity of nucleic acids. Proteins: All cells use left-handed amino acids to make proteins, even though proteins could be composed of right- or left-handed amino acids. Translation: All cells use ribosomes for translationand have highly conserved RNA sequences in ribosomes. Genetic code: All cells use almost the same geneticcode for translating mRNA into proteins, despite the huge number of possible codings. LUCA-last common ancestor of bacteria, archae, andeukarotes, oxygenic photosynthesis and aerobic respiration is not likely to be present in LUCA LUCA-Traits that are not obviously essential oroptimal yet they are still shared by all cellular life LUCA- most likely present is ATP, DNA genome, prokarytoiccell, and ribosomes 11.1.3Summarize current understanding of the timeof origin of life on Earth T he Earth formed4.54 billion years ago (Ga). Evidencesuggests that life existed as early as3.8 Gaand possibly by4.1 Ga, implying thatlife emerged soon after the presence of liquid water. 1.2 Eukaryotic cells arose from prokaryotic ancestors just once 1 [eukaryotes] 11.2.1List features that are present in all eukaryotesbut are absent from prokaryotes ucleuswith a double membrane andgenomeinside. N Organellessuch asendoplasmic reticulum,Golgi apparatus,andmitochondria. Complexendomembrane systemand larger cell volumecompared to prokaryotes. They both have plastids, ribosomes , prokaryotes don’t haveendomembranesystem 1.2.2Draw the relationships of Bacteria, Euryarchaea,TACK archaea, and the eukaryotic 1 nucleus E ukaryotesare more closely related toTACK archaeathan toEuryarchaeaor Bacteria. Eukaryotic mitochondria, however, are derivedfromalpha-proteobacteria. 11.2.3Explain why the origin of eukaryotes was animportant evolutionary event T he origin of eukaryotes enabledgreater cellularcomplexityand the evolution of multicellularity, allowing for a wider range of ecologicalroles and adaptation. 1.3 Eukaryotes arose as a merger of a bacterial (mitochondria) and TACK archaeal 1 lineage [endosymbiosis] 11.3.1List evidence that supports the endosymbioticmodel M itochondriahave acircular genomelike bacteria. Mitochondria and alpha-proteobacteria sharesimilar ribosome structureand biochemical reactions. Mitochondriadivide independently, indicating a cell-likeorigin. 1.3.2 Draw the phylogenetic trees that would be expected under the endosymbiotic or 1 autogenous theories for the origin of mitochondria and plastids In theendosymbiotic theory, mitochondria are moreclosely related to alpha-proteobacteriathan to the nuclear genome. In theautogenous theory, mitochondria are more closelyrelated to theeukaryotic nucleus. Phylogeneticanalysiscan be used to test theendosymbiotictheoryfor the origin of mitochondria or plastids Phylogenetic speciesfocus on the degree of relatedness Biological speciesfocus on the ability to interbreed 1.4 There are two models for the origin of the nucleus and endomembrane 1 system [topological models] 11.4.1Summarize differences between the outside-inand inside-out models O utside-in model: Thecell membrane folds inward,forming internal vesicles, the nucleus, and the endomembrane system,internalizationoftheplasmamembrane Inside-out model: Theoriginalcellbody pushesmembranesoutward, fusing to create thecytoplasmand internal compartments, withmitochondria originally external. Phylogentic analysiscannot be used to distinigishthe inside-out and outside-in models because both models areautogenousand posit thatthe nucleus is derived from an archaealancestor. Membranes don't have genomes, so there is no way to usephylogenetic analysisto tell if the nuclear membrane came from the plasma membrane or vice versa 1.4.2Explain why the recent characterization ofAsgard archaea supports the inside-out 1 model A sgardarchaeota(e.g.,Lokiarchaeota) produceextracellularprotrusionsand interactcloselywithectosymbioticprokaryotes, supportingthe idea of membrane extension outward, consistent with theinside-outmodel Closet relatives of eukaryotes so far discovered Oxygenicphotosynthesis- H2O is the electron donor - oxygen gas is produced as a byproduct - change to the atmosphere that allowed for the evolution of large aerobically repairing A species such as eukaryotes - therustingof the oceans as dissolved Fe(II) was oxided into reddish Fe(III) - Theaccumulation of ozonewhich shielded the earthfrom ultraviolet light and heped make land more easily colonized - Cyanobacteriaconvert carbon dioxide and water intocarbohydrates and oxygen using light energy noxygenicphotosynthesis- H2S is the electron donor A 13.1 Humans are a lineage of primates [Hominid relationships] 13.1.1 Identify primate traits that are adaptations for arboreality and frugivory A rboreality (tree-dwelling): Primates havebinocularvision,flexible shoulder joints, andgrasping handswith opposable thumbs, all of whichhelp in navigating through trees. Frugivory (fruit-eating): Primates havecolor visionto identify ripe fruit anddextrous handsto grasp and manipulate fruit. Last common ancestor of living primates adapted throughliving in forests and climbing trees 3.1.2 Summarize the relationships between humans and the other apes (chimps, gorilla, 1 orangutans, and gibbons) H umans are part of thegreat ape cladeand are mostclosely related tochimpanzees andbonobos, with the last common ancestor divergingaround7 million years ago. Other great apes includegorillasandorangutans,whilegibbonsare in a sister clade of the great apes. 3.2 Humans evolved many differences from other great apes in the last 6 million years 1 [Hominin evolution] 3.2.1 List important morphological and behavioral differences between humans and 1 other primates, including bipedality, cooking, hair loss, language, meat eating, opposable thumb, overarm throwing ipedality: Humans are fully bipedal, walking on twolegs. B Cooking: Humans cook food, which influences diet anddigestion. Hair loss: Humans have significantly less body haircompared to other great apes. Language: Humans have complex language, allowing abstractcommunication. Meat eating: Humans have adapted to a diet that includesa significant amount of meat. Opposable thumb: Humans have afully opposable thumbthat allows precise tool use and manipulation. O verarm throwing: Humans can throw with remarkable speed and accuracy, a key trait in hunting. Humanshave knees that lock in extension, a twisted upper arm, bipedality thangreat apes They both sharemaking nocturnal shelters, livingin complex social groups and making tools Adaptations in humans (improving environment);Increasedsweat glands for better cooling on the open savanna Exaptations in humans (not originally intended);binocularvisionwhich allows us to judge distance when throwing projectiles, agraspinghandthat can hold a spear or stone tool, aflexbile shoulder jointthat allowsefficient throwing , the flexible shoulder joint originally evolved for adifferent purpose,such aslocomotion(e.g., swinging from branches) and waslater co-optedfor throwing Traits evolved in the ancestry of humans from oldest to youngest: flexible shoulder joints, bipdealism and then tools 3.2.2 Explain the purported roles of long-distance running and collective hunting in 1 language and cooperation in modern humans L ong-distance running: Humans evolved traits likesweat glands,long legs, and locked kneesfor endurance running, allowing themto chase prey over long distances in the heat., humans can utrun any other animal over a marathon Collective hunting: Hunting in groups fostered theneed forcooperationandlanguage to communicate and strategize, further enhancing group success and social cohesion. Scavenger hypothesis :the hominins started by scavengingkills from other predators and later transitioned to active hunting 3.3 Anatomically modern humans emerged in Africa about 200,000 years ago and 1 spread around the world [Modern humans] 3.3.1 Summarize the distribution of genetic variation among human populations and its 1 relation to geography H uman populations aregenetically homogenousdue tofrequentgene flowand the short time span (about200,000 years) since theirorigin. However,allelic variation decreaseswith distance from Africa, reflecting successivegenetic bottlenecksduring human migration out of Africa. Traits such asskinpigmentationhave regional adaptations based onVitamin Davailability, but thereareno biological racesin humans. Humans migrate out of Africa 100 Ka years ago Human language :requires neural processing so thatselection for language also selects for great brain size, allows groups to plan coordinated actions such as when hunting, it is possible to connect concepts together in new ways , coopted to plan ahead and solve complex problems W hen anatomically modern humans moved out of Africa and into Eurasia, they interacted withNeanderthalsandDenisovans—two groupsof archaic humans whose ancestors had migrated out of Africa much earlier. During these interactions, there was someinterbreedingbetween modern humans and these archaic populations, which resulted ina small percentage of Neanderthal andDenisovan DNAbeing present in the genomes of many modern human populations outside of Africa today. However, modern humans eventuallyoutcompeted these archaichumans, leading to their extinction. 10.1 The nature of species is controversial [species concepts] 0.1.1. Distinguish the problem of determining is a group is a valid taxon from determining whether 1 It is at the species rank Determining if a group is a valid taxon involves classifying organisms based on similarities and shared characteristics, which could place them at various taxonomic ranks (e.g., genus, family, or species). Determining if it is at the species rank requires identifyingwhether the lineage is sufficiently distinct from others to warrant a separate species designation,typically done through biological or phylogenetic criteria. TheBiological Species Conceptviews speciesasgroups of interbreeding organisms, while thePhylogenetic Species Conceptviews speciesasclades (monophyletic groups). 0.1.2. Explain key differences between biological and phylogenetic species concepts. 1 TheBiological Species Conceptdefines species basedonthe ability of their members to reproduce with one another and to be unable to reproduce with members of other species. It focuses on reproductive isolation. ThePhylogenetic Species Concept,on the other hand, defines species as clades (monophyletic groups)and emphasizesgeneticdifferences that make a lineage distinct for practical reasons rather than focusing on reproductive isolation alone. 10.2 Species may contain discrete races/varieties [subspecific variation] 0.2.1. Recognize cases where species can or cannot be divided into races/varieties. 1 Species can be divided intoraces/varietieswhen thereisgenetically discrete variationthat is sufficiently distinct to justify recognition, such as inblack bears (Ursus americanus), which are divided into12 subspeciesbased ongenetic differentiation.When genetic differences are not significant or are clinal rather than discrete, races/varieties are not recognized. For example,humans do not have genetic racesbecause their genetic variationisclinaland not discrete. - Geographic and genetic distancecorrelate/the same because the more distant populations are, the lower the rate of exchanging genes 0.2.2. Explain why humans lack genetic races/varieties. 1 Humans lack genetic races because they area geneticallyhomogenous specieswithno clear geographic breaks in genetic variation. Thegenetic differences in humans areclinal rather than discrete, with only about7% of geneticvariation being structured geographically, while~93% of genetic variation isshared among all populations. herefore,there are no sufficiently distinct local populationsto justify the recognition of T biological races. - Human speciesare not subdivided into biological races because the amount of genetic differentiations between human populations is relatively low, and genetic diversity in humans is clinical rather than organized into discrete - biological speciescanbe divided into subgroups ifthere is enough genetic differentiation, as is seen in many other animal species. 0.3. The splitting of an ancestral lineage into independently evolving descendant 1 lineages can occur without prior geographic isolation [speciation] 0.3.1. Distinguish allopatric from sympatric speciation 1 Allopatric speciationoccurs due togeographic isolation,where populations become separated and evolve independently until they become distinct species. This process can happen throughdispersal to an isolated locationorenvironmental changessuch as climate change or shifting water levels.The splittingof the ancestral population into geographically Isolated regions prevent them from exchanging genes. In contrast,sympatric speciation Occurswithout geographic separationbut involvesstrong disruptive selection and assortative mating (consistent), where individuals preferentially mate with others of similar trait values. (most common way that sister species come to be unable to interbreed) - Factors that cause divergence from members of species that are isolated; natural selection occurring in different environments, genetic drift acting on pre-existing variation and new mutations 0.3.3 Describe how disruptive selection and assortative mating can, potentially, lead to 1 the evolution of assortative mating, and why this is needed for speciation to occur Disruptive selectionfavors extreme trait values overintermediate ones, while assortative matingmeans that individuals preferentiallymate with others who share similar traits (e.g.,long-legged spiders preferentiallymating with other long-legged individuals). Insympatric speciation,both disruptiveselection and assortative matingare needed for the population to split intoseparate breeding groups, which can then diverge over time and become different species. Fst - A Measure of genetic differentiation between populations Reproductive isolation - Not evolve within a single population - Individuals that cannot mate with other members of their populations generally have lower fitness hanges in trait function contributed to the evolution of some complex phenotypes C [exaptation] .1.1. Distinguish adaptation from exaptations based on whether the current function of a 9 trait is that for which it originally evolved. A nadaptationis a trait that evolved specifically for itscurrent function, while an exaptationis atrait that evolved for one functionand later became important for a different function. For example,feathersoriginallyevolved forthermoregulationbut were latercooptedforflight, making them an exaptation. .2 Sexual selection can favor traits that lower survivorship but increase reproductive 9 success [sexual selection] .2.1. Recognize examples of secondary sexual characteristics as being the result of 9 sexual selection. E xamples ofsecondary sexual characteristicsthatresult fromsexual selection include themale peacock's large and colorful tail,theshowy colors of a male mandrill, and thehorns of a rhinoceros beetle. Thesetraits evolve because they increase reproductive success, even if they decreasesurvivorship. Sexually dimorphic :no differences, both specieslook the same Monogamy :males and females share similar roles,male mates with one female , minimal or no visible differences Polygamous :one male mates with many females, maleshave higher variance in reproductive success, some males leave very many offspring, but most dont lives any offspring ,resulting in sexual dimorphism , malesand females usually have distinct physical differences because males compete with each other for mating opportunities. .2.2. Explain why exaggerated secondary sexual characteristics mainly evolve when 9 there is a high variance in reproductive output, which is more commonly seen in males. E xaggerated secondary sexual characteristicsmainlyevolve in species withhigh variance in reproductive output, especially inpolygamous species. In such species, one male mates with many females, while others do not reproduce at all. Thishigh variancemeans that any trait that helps a male successfullycompete for mateshas a large payoff, even if itreduces survivorship. Because males often differ greatly in mating success,selection more strongly favors traits that improve mating success (even if they lower survival). .3 Natural selection can act when traits affect fitness of units above the individual 9 [group selection] .3.1. Explain why individual level selection cannot explain the evolution of cooperation 9 or altruism. Individual-level selectioncannot explaincooperation or altruismbecause these behaviorsreduce individual fitnesswhile increasingthefitness of others.Altruistic traitswould beselected againstif natural selection acted only at the individual level, as they would lower the individual's chances of survival and reproduction. .3.2. Associate group selection with cases where the genetic composition of groups 9 affects group fitness. G roup selectionoccurs whengroups with more altruistshave disproportionately higher reproductive outputcompared to groups withfewer altruists. This mechanism can lead to theevolution of altruistic traitsevenif such traits lower individual fitness. Thegroup composition—with a higher proportion ofaltruists—improves the overall fitness of the group, thereby increasing the prevalenceof altruism. .1 Heritability describes the extent to which variation in a continuous trait has a genetic 8 basis [heritability] .1.1. Explain how additive effects over many polymorphic loci can yield a bell-shaped 8 distribution of trait variation. C ontinuous traits, such asheight, are controlledbymultiple allelesacrossmany loci in the genome. Theinteraction of alleles at differentlocican combine in many ways, resulting in abell-shaped distributionof trait values.Individuals withextreme values have either all "tall" or all "short" alleles, whilemedium trait valuesresult from havinga mix of tall and short alleles. .1.2. Define heritability (h²) as the fraction of phenotypic variation in a population that is 8 predictable given parental trait values. H eritability (h²)is defined as thefraction of thevariation in a population that can be explained by genetics. It indicates how wellan offspring’straits can be predicted given the traits of its parents. .1.3. Describe how h² helps predict the degree to which a trait value responds to 8 directional selection. H eritability (h²), along with thestrength of selection (s), is used to calculate the response to selection (r), using the equationr = h² * s. This helps predicthow much the mean trait valuein the population will change after one generation ofdirectional selection. Directional selection mean will increase, standard deviation will decrease Stablizing selection mean will increase 8.2 Eugenics has scientific and ethical flaws [eugenics] .2.1. Describe how correlations between parental and offspring environments can result 8 in an overestimation of heritability. In humans, thesocial environmentsof parents and offspring are often correlated (e.g., children growing up in poverty are likely to have parents who also grew up in poverty). This correlation results in anoverestimation of heritabilitywhen trying to determine if traits likecriminality or educational attainmentare inherited. Eugenicistsover estimated the heritabltiy of human traits. They failed to account for the fact that parents and offspring typicallygrow up in relatively similar environments 8.2.2. Explain how purely environmental factors can change human social traits. E nvironmental factors, such asnutritionorsocialupbringing, can have significant effects on human social traits. For example, improvingnutritional practicescan increase average heightover time, and a supportivesocial environment can lead to bettereducational outcomes. .3 Selection can act not only on the mean but on the variance of a continuous trait 8 [stabilizing and disruptive selection] .3.1. Distinguish stabilizing and disruptive selection based on the relative fitness of 8 different trait values and predict their results. S tabilizing selectionfavors trait valuestowardsthe centerof the distribution, disfavoring extreme values, and leading toreduced variance. For example,babies with moderate birth weightshave higher survival rates than those with very low or very high birth weights. Disruptive selection, on the other hand,favors extremetrait valuesat both ends of the distribution, leading toincreased variance. Anexample would be abird population in whichboth large and small beaksare advantageousfor different food sources, while medium-sized beaksare less effective. .1 The frequency of genetic disorders is based on a balance between the rate of 7 mutation and the strength of negative selection [mutation-selection balance] .1.1. Identify a higher mutation rate and milder symptoms as factors increasing disease 7 prevalence. A higher mutation rate leads to more deleterious allelesarising in a population. Additionally,genetic disorderswithmilder symptoms,such asfamilial hypercholesterolemia, areless strongly selected against,allowing those alleles to persist at higher frequencies in the population. .1.2. Explain why alleles causing recessive disorders are at a higher frequency than 7 dominant alleles. R ecessive alleles tend to be at higher frequenciesbecause theyonly cause disease in homozygous individuals, which are relativelyrare when the allele frequency is low.Heterozygotesdo not exhibit symptoms,which allows the allele to increase in frequencywithout being strongly selected against.Dominant alleles, on the other hand,cause disease in heterozygotesand thus areselected against immediatelywhen they arise,keeping their frequencylow. .2 Genetic disorders vary in frequency among populations, especially small, inbred 7 populations [inbreeding] 7.2.1. Identify genetic drift as the cause of variation among populations. G enetic driftis responsible forvariation in genetic disorder frequencies among different populations, particularly in small or inbred populations.In such populations,random chancecan lead to certain deleterious alleles being present at higher frequenciesthan expected, as seen inethnic groupslike theAshkenazi Jews andOld Order Amish. recessive disease allele might be found at higher frequency in an inbreeding population than would be expected under mutation-selection balance, Because inbreeding populations are small, genetic drift can result in a deleterious allele attaining a higher-than-expected frequency by chance. .3 Over-dominant selection tends to maintain polymorphisms in a population [balanced 7 polymorphism] .3.1. Determine whether over-dominant selection is occurring based on the relative 7 fitness of the three genotypes. O ver-dominant selectionoccurs when theheterozygotegenotypehas ahigher fitnessthan eitherhomozygote genotype. For example,in populations with high malaria infection rates, theAS heterozygotesforthesickle-cell allelehavehigher fitnesscompared toAA or SS homozygotes, providingresistance to malariawithout the severe anemia associated with sickle-cell disease. .3.2. Explain why over-dominant selection tends to prevent either allele from going to 7 fixation. Inover-dominant selection, therarer alleletendstoincrease in frequencybecause heterozygotes have the highest fitness. This processleads to abalanced polymorphismwhereboth alleles are maintainedatan intermediate frequency, preventing either allele fromgoing to fixation.
