Evidence of Evolution by Natural Selection. Dodo bird

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1 Evidence of Evolution by Natural Selection Dodo bird

2 Evidence supporting evolution Fossil record transition species Anatomical record homologous & vestigial structures embryology & development Molecular record protein & DNA sequence Artificial selection human-caused evolution

3 Fossil record Layers of sedimentary rock contain fossils new layers cover older ones, creating a record over time fossils within layers show that a succession of organisms have populated Earth throughout a long period of time

4 Fossil Record

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6 Fossil record A record showing us that today s organisms descended from ancestral species

7 Body size (kg) Evolutionary change in horses Mesohippus Hyracotherium Merychippus Equus Nannippus Millions of years ago

8 Evolution of birds Archaeopteryx lived about 150 mya links reptiles & birds Smithsonian Museum, Washington, DC

9 Land Mammal????

10 2006 Fossil Discovery of Early Tetrapod Tiktaalik missing link from sea to land animals

11 Anatomical record Homologous structures similarities in characteristics resulting from common ancestry

12 Homologous structures Similar structure Similar development Different functions Evidence of close evolutionary relationship recent common ancestor

13 Homologous structures spines leaves succulent leaves needles tendrils colored leaves

14 Analogous structures Separate evolution of structures similar functions similar external form different internal structure & development different origin no evolutionary relationship Don t be fooled by their looks! Solving a similar problem with a similar solution

15 Convergent evolution Flight evolved in 3 separate animal groups evolved similar solution to similar problems analogous structures Does this mean they have a recent common ancestor?

16 Convergent evolution Fish: aquatic vertebrates Dolphins: aquatic mammals similar adaptations to life in the sea not closely related Those fins & tails & sleek bodies are analogous structures!

17 Parallel Evolution Convergent evolution in common niches filling similar ecological roles in similar environments, so similar adaptations were selected but are not closely related marsupial mammals placental mammals

18 Parallel types across continents Niche Placental Mammals Australian Marsupials Burrower Mole Marsupial mole Anteater Anteater Numbat Nocturnal insectivore Mouse Marsupial mouse Climber Spotted cuscus Lemur Glider Flying squirrel Sugar glider Stalking predator Ocelot Tasmanian cat Chasing predator Wolf Tasmanian wolf

19 Vestigial organs Modern animals may have structures that serve little or no function remnants of structures that were functional in ancestral species deleterious mutations accumulate in genes for non-critical structures without reducing fitness snakes & whales remains of pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone This is not LaMarck s loss from disuse!

20 Vestigial organs Hind leg bones on whale fossils Why would whales have pelvis & leg bones if they were always sea creatures?

21 Comparative embryology Similar embryological development in closely related species all vertebrate embryos have similar structures at different stages of development gill pouch in fish, frog, snake, birds, human, etc.

22 Nucleotide substitutions Molecular record Comparing DNA & protein structure universal genetic code! DNA & RNA compare common genes cytochrome C (respiration) hemoglobin (gas exchange) Closely related species have sequences that are more similar than distantly related species DNA & proteins are a molecular record of evolutionary relationships Horse/ donkey Sheep/ goat Rabbit/ rodent Llama/ cow Why compare these genes? Pig/ cow Dog/ cow Human/ cow Horse/cow Goat/cow Millions of years ago Human/kangaroo Human/rodent

23 Comparative hemoglobin structure Human Macaque Dog Bird Frog Lamprey Why does comparing amino acid sequence measure evolutionary relationships? Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans

24 Building family trees Closely related species (branches) share same line of descent until their divergence from a common ancestor

25 Artificial selection Artificial breeding can use variations in populations to create vastly different breeds & varieties descendants of wild mustard descendants of the wolf

26 Natural selection in action Insecticide & drug resistance insecticide didn t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective

27 "Nothing in biology makes sense except in the light of evolution." -- Theodosius Dobzhansky March 1973 Geneticist, Columbia University ( )

28 Evolution is "so overwhelmingly established that it has become irrational to call it a theory." -- Ernst Mayr What Evolution Is 2001 Professor Emeritus, Evolutionary Biology Harvard University ( )

29 Natural Selection Organisms that are best adapted to their environment are more likely to survive and reproduce Remember! Adaptation = helpful mutation

30 Artificial Selection Humans select and breed organisms for traits that are desirable. Examples: Dogs Plants

31 Natural Selection & Phenotype Review: What is a phenotype again??? An observable, physical characteristic of an organism ie. Hair color, eye color, height etc Natural selection acts directly on the phenotype of an organism. An organisms is best fit to survive in its environment based on its physical characteristics Best fit organisms passes its genes down to more offspring

32 Gene Pools & Allele Frequency All of the genes within a population including the different alleles for each gene make up the gene pool. Scientists study gene pools by examining allele frequency or how common a given alleles is in comparison with the total number of alleles for that gene.

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34 How does this relate to evolution? Evolution involves a change in the frequency of particular alleles in a population over time. Evolution works on populations as a whole whereas natural selection works on individuals.

35 Genetic Drift Random change in the frequency of the alleles in a gene pool. Bottleneck effect population cut down dramatically Founder effect small group starting a new population

36 Founder Effect

37 Bottleneck Effect

38 How do allele frequencies change? For single gene traits - natural selection can causes changes in allele frequency and thus, change phenotype frequencies.

39 How do allele frequencies change? For polygenic traits - natural selections affects the relative fitness of phenotypes and therefore creates 3 possible selection patterns: Directional selection Stabilizing selection Disruptive selection

40 Directional Selection Occurs when organisms at one end of the curve have a higher fitness than those in the middle or other end Curve shifts in the direction of the best fit animal

41 Stabilizing Selection Individuals near the center of the curve are best fit to survive Curve narrows and remains in the same place