Before Natural Selection o Recall that Darwin was
Before Natural Selection o Recall that Darwin was not the 1 st to think about how species have changed over time n Aristotle’s Scala Naturae grouped species with similar “affinities” n n n together Linnaeus came up with Binomial Nomenclature and classified based on physical similarity Cuvier noted that fossils of species differed significantly from more modern forms (proposed the idea of Catastrophism-that changes happened b/c of catastrophic events, and not gradually) Lamarck suggested that use/disuse could change an organism’s body to fit the environment (he thought that acquired traits were heritable) o Malthus discussed population limits o Others before Darwin worked with how the planet changed: n Hutton proposed that geologic features were the result of gradual changes that are still occurring today n Lyell took this a step further and proposed his principle of Uniformitarianism-mechanisms of change are constant over time
Figure 24 -1 Aristotle proposed that species were organized into a sequence based on increased size and complexity, with humans at the top Humans Vertebrates Invertebrates Land plants Green algae Fungi Simple cells
Darwin’s Observations and Inferences o Observations: n Members of a population vary greatly in their traits n Traits are inherited from parents to offspring n All species are capable of producing more offspring than their environment can support n Because of lack of resources, many offspring do not survive o Inferences (Summary of Natural Selection’s Mechanism): n Individuals whose inherited traits give them a higher probability of surviving and reproducing in an environment tend to leave more offspring (have greater reproductive success) n This inequality means that favorable traits accumulate in populations over multiple generations
Natural Selection o Aka “Descent with Modification” was Darwin’s proposal for how species change over time and was the result of careful study over his Galapagos Island collections. o Darwin’s main focus was on adaptations that allowed species to survive better in their environments-finches had beaks adapted to their food source. o Recall that while Darwin came up with the idea first, Alfred Russell Wallace also had the same idea, with no knowledge of Darwin’s work.
o Remember: n Populations evolve, individuals do not n Traits influenced by natural selection must be heritable n Environments are moving targets, so there’s no “perfect” and what is good in one population is not necessarily good in another
Directly Observable Evidence for Natural Selection o o The Fossil Record n We can see trends in the evolution of species n n n Similar patterns of fetal development Homology (forelimb picture) Vestigial structures n Looking at what we think happened to the geographic features of the planet to explain distribution of species (ex: how Pangea’s split allowed us to predict where we would find certain types of fossils) Anatomical Features Biogeography Molecular Similarity n Studies of DNA sequence and amino acid sequence can be used to construct “molecular clocks” that give us clues to which organisms diverged from one another, and tells us relatively how long ago the divergence occurred Current Real-Life Experimentations o Predation and Coloration in Guppies n n o Pools of guppies w/high predation produce more drab colored males There are numerous examples of these “natural experiments” done by scientists Drug-resistant HIV and other “superbugs”
Figure 24 -11 EVOLUTION OF DRUG RESISTANCE Lung tissue Bacteria with point mutation in rpo. B gene M. tuberculosis 1. Large population of M. tuberculosis bacteria in patient’s lungs makes him sick. 2. Drug therapy begins killing most M. tuberculosis. Patient seems cured and drug therapy is ended. However, a few of the original bacteria had a point mutation that made them resistant to the drug treatment. 3. The mutant cells proliferate, resulting in another major infection of the lungs. The patient becomes sick again. 4. A second round of drug therapy begins but is ineffective on the drugresistant bacteria. The patient dies.
Figure 24 -3 110 myo ammonite shell 50 myo bird tracks 20, 000 y-old sloth dung
Figure 24 -9 Humerus Radius and ulna Carpals Metacarpals Phalanges Turtle Human Horse Bird Bat Seal
Figure 24 -8 Gill pouch Tail Chick Gill pouch Tail Human Gill pouch Tail House cat
Figure 24 -5 The human tailbone is a vestigial trait. Capuchin monkey tail (used for balance, locomotion) Human coccyx Goose bumps are a vestigial trait. Erect hair on chimp (insulation, emotional display) Human goose bumps
Figure 24 -7 Amino acid sequence (single-letter abbreviations): Aniridia (Human) Gene: eyeless (Fruit fly) Only six of the 60 amino acids in these sequences are different. The two sequences are 90% identical.
Divergent vs. Convergent evolution o In many cases, evolutionary trees are created in order to show species evolved from common ancestors n Sometimes, this happens b/c of adaptive radiation-when organisms evolve in a variety of directions in order to exploit different aspects of the environment o Occasionally, organisms resemble each other, not because they are related, but because some characteristics are advantageous regardless of their ancestry n Ex: sugar gliders in Australia look like flying squirrels, Octopus eye
Figure 27 -11 Adaptive radiations produce star phylogenies. Star phylogeny (a large polytomy) Rapid speciation Hawaiian honeycreepers underwent adaptive radiation. Hawaiian silverswords underwent adaptive radiation.
Figure 24 -15 b Darwinian evolution produces a tree of life. Bacteria Archaea Green algae Common ancestor of all species living today Land plants Invertebrates Vertebrates Fungi The branches on the tree represent populations through time. All of the species have evolved from a common ancestor. None is higher than any other
The survival of the fittest. . . o Remember, fitness is relative, and “struggle” is not always direct conflict. o Depending on which traits are favored, there are 3 ways in which natural selection can influence phenotypic variation n Stabilizing selection-average is favored n Directional selection-one extreme phenotype is favored n Disruptive selection-both extreme phenotypes are favored
Figure 25 -4 Stabilizing selection reduces the amount of variation in a trait. Normal distribution Mortality Before selection Low High fitness Low fitness During selection After selection For example, very small and very large babies are the most likely to die, leaving a narrower distribution of birth weights. Reduction in variation Heavy mortality on extremes
Figure 25 -3 Directional selection changes the average value of a trait. Normal distribution For example, directional selection caused average body size to increase in a cliff swallow population. Original population (N = 2880) Before selection Survivors (N = 1027) Low fitness During selection After selection Change in average value High fitness Change in average value
Figure 25 -5 Disruptive selection increases the amount of variation in a trait. For example, only juvenile black-bellied seedcrackers that had very long or very short beaks survived long enough to breed. Normal distribution Before selection Only the extremes survived High fitness Low fitness High fitness During selection After selection Increase in variation Only the extremes survived
Evolution of Populations o This is fueled by genetic variation n For individuals, can be quantified using average heterozygosity (average % of genes for which an individual is heterozygous) n For populations, you can directly compare individual karyotypes or gene sequences from each population o Sometimes, the difference is dramatic, and sometimes the difference is a cline (gradual difference) o This often exists b/c of geographic variation (isolation) o Genetic Variation occurs for 2 reasons n Sexual Reproduction n Mutation is the ultimate source for most new genetic variations. Often these mutations are neutral, but occasionaly, you get an adaptive mutation. The rates at which mutation occurs varies between species.
Hardy-Weinberg o Mathematical model for testing whether or not a population is evolving. o This is a mathematical model: n n p=frequency of the dominant allele q=frequency of the recessive allele p+q=1 p 2+2 pq+q 2=1 (represents the combinations of alleles or genotypes) o To utilize H-W in determining if a population is evolving, scientists must apply the model over time with many generations.
Figure 24 -10 If heritable variation… A 1 A 1 A 1 A 2 A 2 A 2 A 1 A 1 A 2 A 2 Color varies among individuals primarily because of differences in their genotype … leads to differential success… A 1 A 1 A 1 A 2 A 1 A 1 A 2 A 2 Birds find and eat many more dark-winged moths than light-winged moths … then evolution results. Allele frequencies have changed in the surviving moths
Figure 25 -1 -1 A NUMERICAL EXAMPLE OF THE HARDY-WEINBERG PRINCIPLE Allele frequencies in parental generation: Allele A 1 = p = 0. 7 Allele A 2 = q = 0. 3 1. Suppose allele frequencies in the parental generation were 0. 7 and 0. 3. Gene pool (gametes from parent generation) 2. 70% of gametes in the gene Offspring pool carry allele A 1, and 30% carry allele A 2. A 1 0. 7 = 0. 49 p p = p 2 A 1 A 2 0. 7 0. 3 = 0. 21 q p = pq A 2 A 1 0. 3 0. 7 = 0. 21 q p = pq 0. 21 + 0. 21 = 0. 42 A 2 0. 3 = 0. 09 q q = q 2 3. Pick two gametes at random from the gene pool to form offspring. You have a 70% chance of picking allele A 1 and a 30% chance of picking allele A 2.
Figure 25 -1 -2 Offspring A NUMERICAL EXAMPLE OF THE HARDY-WEINBERG PRINCIPLE Frequency of A 1 A 1 genotype is p 2 = 0. 49 Frequency of A 1 A 2 genotype is 2 pq = 0. 42 Frequency of A 2 A 2 genotype is q 2 = 0. 49 4. Three genotypes are possible. Calculate the frequencies of these three combinations of alleles. 5. When the offspring breed, 49% of offspring have the A 1 genotype. All will contribute A 1 alleles to the new gene pool. 42% of offspring have the A 1 A 2 Genotype. Half of their gametes will carry the A 1 allele and the other half will carry the A 2 allele. 9% of offspring have the A 2 genotype. All will contribute A 2 alleles to the new gene pool. imagine their gametes entering a gene pool. Calculate the frequencies of the two alleles in this gene pool. 6. The frequencies of A 1 and A 2 Allele frequencies in offspring gene pool 1 p = 0. 49 + 2 (0. 42) = 0. 7 p = frequency of allele A 1 q = 12 (0. 42) + 0. 09 = 0. 3 q = frequency of allele A 2 have not changed from parental to offspring generation. Evolution has not occurred. Genotype frequencies will be given by p 2 : 2 p q : q 2 as long as all Hardy-Weinberg assumptions are met.
Conditions for Hardy-Weinberg to remain at equilibrium (population IS NOT evolving) No mutation Random mating No selection pressure Large population size No gene flow (no immigration or emigration) Rarely do all of these conditions exist at any given moment, but over time, populations tend to be in equilibrium o o o
Size Restrictions o Genetic Drift-caused by small population size or random changes that make predicting gene frequency difficult. 2 examples: n The founder effect-a small number of individuals are isolated and have to reestablish a gene pool (Afrikaner population) n The bottleneck effect-catastrophic events drop population size (cheetah population) o In either case, genetic variation is lost, and harmful alleles can persist even if the population #’s increase.
Figure 25 -6
How do Species Preserve Genetic Variation? o Diploidy-Since organisms get 2 copies of each gene, recessive alleles can be preserved o Balancing Selection-occurs when natural selection maintains 2 forms of a trait in a population n The heterozygote advantage n Frequency-Dependent Selection-as a phenotype becomes more common, it loses the advantage (ex. Mimicry) n Neutral Variation- mutation has little to no effect on phenotype or on reproductive success o Sexual Reproduction
Why isn’t there a “perfect” organism? o Selection can only act on existing genes and phenotypes (each intermediate step must be adaptive) o You cannot scrap ancestral anatomy to build something new (see above statement) o Adaptations are often compromises (multifunctionality means you have to choose a primary function. Ex: seals do not have legs b/c they also swim) o Chance, selection, and the environment have to interact
Types of evolution o Microevolution-evolution of allele frequencies within gene pools o Macroevolution-patterns of evolution over long time spans (like the emergence of new species) o California Salamander Video (3 min. ) Write a definition for the following terms using examples from the video: Camouflage, Mimicry, Hybrid, Species
The Biological Species Concept o A species is a group of populations whose members interbreed in nature to produce fertile offspring n (Hybrids can exist, but are sterile: ligers, mules, etc) o Species are held together by proximity and interbreeding
Keep ‘em separated: o Requires reproductive isolation-barriers that prevent the production of viable offspring n Allopatric: “other country” speciation-occurs when species are geographically isolated n Sympatric: “same country” speciation-occurs when organisms are in the same area but speciate o Prezygotic barriers-block fertilization o Postzygotic barriers-prevent a hybrid from mating successfully
Figure 26 -5 DISPERSAL AND COLONIZATION CAN ISOLATE POPULATIONS. Island Continent 1. Start with one continuous population. Then, colonists float to an island on a raft. 2. Island population begins to diverge due to drift and selection. 3. Finish with two populations isolated from one another. VICARIANCE CAN ISOLATE POPULATIONS. R River iv er chan ges course 1. Start with one continuous population. Then a chance event occurs that changes the landscape (river changes course. ) 2. Isolated populations begin to diverge due to drift and selection. 3. Finish with two populations isolated from one another.
Types of Prezygotic Mechanisms Habitat Isolation- occupy different habitats Temporal Isolation- breed at different times Behavioral Isolation-courtship rituals differ Mechanical Isolation-differences in shape/form prevent mating o Gamete Isolation-Gametes from two different species are not compatible. o o
Types of postzygotic Mechanisms o Reduced Hybrid viability-parental genes prevent the hybrid’s survival o Hybrid Breakdown-Some hybrids can mate with one another, but their offspring are not viable o Reduced Hybrid Fertility-sterility due to inability to produce normal gametes
Speciation Rates-on your practice from yesterday o Darwin originally believed that gradualism only existed (species change at a slow, steady rate over time) o From the fossil record, we now know that punctuated equilibrium exists (periods of equilibrium followed by periods of natural selection) n This can happen very rapidly, and as little as 1 gene can make a species reproductively isolated
Darwin o ". . . I remember well the time when the thought of the eye made me cold all over, but I have got over this stage of the complaint, and now small trifling particulars of structure often make me feel uncomfortable. The sight of a feather in a peacock's tail, whenever I gaze at it, makes me sick!"
Sexual Selection o This is a variation of natural selection where some traits persist, not because they are advantageous, but because they are attractive o In many cases, the traits that evolve are not fit, but continue to persist o Intersexual Selection is based on the “female choice” model-the opposite sex chooses a mate o Intrasexual Selection is based on competition within the sex for access to mates or resources that will attract mates o Causes sexual dimorphism (variation between sexes) o https: //www. youtube. com/watch? v=4 j 7 GSu 99 Lm. Y
Figure 25 -15 Beetle Scarlet tanager Lion Females Males During the breeding season, males of the Male scarlet tanagers use their bright beetle Dynastes granti use their elongated coloration in territorial and courtship horns to fight over females. displays. Male lions are larger than females lions and have an elaborate ruff of fur called a mane.
Artificial Selection o Humans select the traits we find beneficial in some way: attractive, helpful, cheaper…. . o This has been in place for centuries. o Dog breeding, Agriculture
o Phylogenetic Tree- graphic representation of a classification system based on evolutionary relationships and when things evolved. n Created using several lines of evidence. o Ex. Morphology, embryology, fossil evidence, DNA. n May show multiple splits n General time is included on trees o Cladogram-graphic representation of the evolutionary relationships between a small group or fewer groups of organisms. n Relationship based on the presence of certain derived characteristics. Ex. Presence of feathers in birds or # of amino acids in mammals. n Only branches into two (bifurcations)
Figure 27 -11 Adaptive radiations produce star phylogenies. Star phylogeny (a large polytomy) Rapid speciation Hawaiian honeycreepers underwent adaptive radiation. Hawaiian silverswords underwent adaptive radiation.
Phylogenetic Tree Problem Draw a phylogenetic tree to describe the following scenario: o Dingles were present just 1, 000 years ago, when they first evolved. Whozits and Whatzits quickly evolved from Dingles (100 years later), when the Dingles became extinct. The Whozit line continued unchanged until the present, while the Whatzits formed 3 other species before dying off; Floogles, Naks, and Surps (300 years before today).
Cladogram Activity o Complete one of the following activities: n Hardware Organism Key/Cladogram OR n Cytochrome c Lab (chart, cladogram, questions #1 -5) o Write a paragraph summarizing your results, your activity and the other activity. *See Questions*
Figure 24 -15 b Darwinian evolution produces a tree of life. Bacteria Archaea Green algae Common ancestor of all species living today Land plants Invertebrates Vertebrates Fungi The branches on the tree represent populations through time. All of the species have evolved from a common ancestor. None is higher than any other
Geologic Time o This is a time scale that uses the fossil record to trace the major events in the planet’s history o Dates are determined by dating fossils n Relative Dating-accomplished via the law of superposition n Absolute Dating-accomplished via radiometric dating
Figure 27 -5 HOW FOSSILIZATION OCCURS 1. A tree lives in a Seeds Pollen Leaves swampy habitat. The tree drops leaves, pollen, and seeds into the mud, where decomposition is slow. 2. The tree falls. The trunk and branches break up as they rot. 3. Flooding brings in sand mud, burying the remains of the tree. 4. Over millions of Sand gravel Buried material from swamp Bedrock years, the mountains erode and the swamp is filled with sediment. The habitat dries.
Earth’s History o Earth is believed to have existed for 4. 6 billion years o Life on earth is believed to have originated 3. 5 billion years ago. n The first life forms were probably prokaryotes o There have been 5 mass extinctions over the history of the planet, and in each, the dominant group of organisms was replaced by another group
rs fro t o m cea sp ns ac ; h e ea O en v rig ds y b Fi in om rs of ba ce t ev life rd lls id m en en ce t of ph ot os yn th et ic Fi rs ph t ev ot id os en yn ce th o es f o is xy Fi ge rs ni (in t ro c at ck m s os co Fi ph nt rs er ain te e in uk an g ar d ox yo oc yg tic ea en Fi f n) os rs tp si ls ho to sy nt he tic eu Fi ka rs ry of t re ot es se d xu alg al ae st ; f ru irs ct t ur ev es id en Fi rs ce t Fi li rs ch sy t sp en m o -li co me ng ke m tr es org pl ic ; f a et an irs ni el im t sm y ox als bila yg ; o te en ce ral at an ly ed Fi Fo M rma o t Ea on ion rth for of m Li fo s sol ar qu rm sy at id i st o w e at n c er om m on pl Ea et rth e Figure 27 -8 a The Precambrian (Hadean, Archaean, and Proterozoic Eons) atmosphere. Hadean Eon Millions of years ago (mya) Archaean Eon All life is unicellular included the origin of life, photosynthesis, and the oxygen Proterozoic Eon Multicellular organisms begin to diversify slowly Position of the continents unknown Most of Earth is covered in ocean and ice.
Figure 27 -8 b Algae abundant, marine invertebrates diversify Echinoderms (sea stars, sea urchins) diversify Coral reefs expand Devonian First upland plant communities (evergreen forests), diversification of fish, emergence of amphibians Insects diversify, coal-forming swamps abundant, sharks abundant, radiation of amphibians pt ile s yc Fi rs et e in t v fu pl es ng an se i ts ls re Fi rs tb as id io m ke -li m al am tm Coal-forming swamps diminish; parts of Antarctica forested ana Gondw Climate cold; extensive ice in Gondwana Supercontinent of Laurentia to the north and Gondwana to the south. Climate mild. ea ng Supercontinent of Gondwana forms. Oceans cover much of North America. Climate not well known. Permian Pa ana rs Pennsylvanian Laurentia ndw Go Fi Carboniferous Mississippian Mass extinction Silurian Mass extinction Ordovician Fi rs ve t co rt m Ar ebr b j th at el fir ro es, lies st po o , a ec ds the rt hi d r p hro no ive h p de rs yla od s, rm ify ; Fi rs an t b im ryo a z Fi l ph oan rs t l ylu s (n m e an ) we d pl st Fi an rs t s Fi t m rs y t c co ar rrh til iz ag al in fu Fi ou ng rs s i( tb fis G on h lom y al fis es h Fi Cambrian rs t Fi ins rs e c Fi t fis ts rs h t as fe wi c rn th Fi om s, jaw rs yc va s t e s Fi tre te cu rs e- fu la Fi t w siz ng r p r i e i l Fi st t nge d p , lic ant rs et d h s Fi t s ra in lant en , s rs e po s s on t p ed d ec la pl s ( ts la nt an am nd s ts p w Fi hi i th rs bi an tr le ep av s) til es es diversification of animals, land plants, and fungi. ) Phanerozoic Eon: The Paleozoic Era included the origin early Supercontinent Pangea assembles. Building of Appalachian Mountains ends. Climate warm; little variation.
Figure 27 -8 c Gymnosperms become dominant land plants; extensive deserts no sa ur rs id t Fi an di rs g no t b io sa ird sp ur e (A rm rc (f ha lo eo we pt rin er g yx p ) lan Fi rs t) tc en Fi tri rs c di Fi t w at rs a om t m te r s ag lil i no es lia -fa m Fi ily rs pl Fi t be an rs e ts tp ; f i r la s ce t a nt nt al m am m al s Gymnosperms continue to dominate land gea Pangea begins to break apart; interior of continent still arid. Cretaceous Dinosaurs diversify Mass extinction tt rs Fi Fi am tm rs Fi Jurassic Pan ea Pangea intact. Interior of Pangea arid. Climate very warm. Age of Reptiles. yr an m al s rs au os in td rs Fi Triasssic Mass extinction Fi rs tn ec ta r-d rin ki ng in se ct s Phanerozoic Eon: The Mesozoic Era is sometimes called the Flowering plants diversify Gon dwa na Gondwana begins to break apart; interior less arid. India separated from Madagascar, moves north; Rocky Mountains form. Climate mild, temperate.
Figure 27 -8 d Mammals. Diversification of angiosperms and pollinating insects Continents continue to drift apart. Collision of India with Eurasia begins. Australia moves north from Antarctica. Palms in Greenland Patagonia. Strong drying trend in Africa and other continents; grasslands form. Alps and Himalayas begin to rise. Ea rli e Ho st h om m sa o in pi in en s s ld da est is po y- ll fa en m f ily ro pl m an ts s pe ta rs Fi Oligocene O ua aq ul ly Fi Paleogene Eocene Paleocene Diversification of mammalian orders tf rs rs Fi Fi rs th or s t p es rim at es tic w ha le s Phanerozoic Eon: The Cenozoic Era is nicknamed the Age of Neogene Miocene Pleistocene Diversification of grazing mammals Continents close to present position. Beginning of Antarctic ice cap. Opening of Red Sea. North and South America joined by land bridge. Uplift of the Sierra Nevada. Worldwide glaciation.
Figure 27 -5 HOW FOSSILIZATION OCCURS 1. A tree lives in a Seeds Pollen Leaves swampy habitat. The tree drops leaves, pollen, and seeds into the mud, where decomposition is slow. 2. The tree falls. The trunk and branches break up as they rot. 3. Flooding brings in sand mud, burying the remains of the tree. 4. Over millions of Sand gravel Buried material from swamp Bedrock years, the mountains erode and the swamp is filled with sediment. The habitat dries.
Major events in Earth’s History: o The earth cools o 1 st life forms o Accumulation of atmospheric oxygen o 1 st eukaryotes o Multicellular organisms o Animals evolved o Plants and fungi colonized land o Land became colonized by other organisms
Where would life come from? o Recall that Miller and Urey tested Oparin’s primordial soup hypothesis and were able to create biochemicals o Lab experiments since then have been able to form polymers in conditions similar to early earth o RNA was probably the 1 st genetic material n These have been shown to be produced abiotically in the lab n Recall that Ribozymes exist as well. o Protobionts can self-assemble n These are aggregates of abiotically produced molecules that form “membranes” and often can sustain chemical reactions (like a metabolism)
What about Eukaryotic cells? o One current hypothesis, the endosymbiant hypothesis tries to explain this n Mitochondria have their own DNA, resemble bacteria, and replicate themselves for cell division n This suggests that once the 1 st primitive cells evolved, they “swallowed” other cells. It is believed that they could have become dependent on one another to carry out parts of their metabolism
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