Evidence for Evolution

Types of Evidence for Evolution Fossil Record (ex: horses and whales) Biogeography Comparative Anatomy Homologous Structures Vestigial Structures Comparative Embryology Molecular Biology / Biochemical evidence Protein (aa sequence) comparisons DNA sequence comparisons

Fossil Record Evidence: Horse evolution one toe on ground (#3), long teeth good for eating tough blades of grass four toes on ground (#2-5), short teeth good for eating soft leaves on shrubs & trees

Look at how the bones in horse feet have changed over time. They became longer and more streamlined, enabling horses to run faster to avoid predators. mya = million years ago

Whale Evolution

Fossil Record of Whale Evolution Pakicetus (terrestrial) Rhodocetus (predominantly aquatic) Pelvis and hind limb Dorudon (fully aquatic) Pelvis and hind limb Balaena (recent whale ancestor)

A lesson in Biogeography

The Wallace Line Read this interesting article by Jared Diamond (author of Guns, Germs, and Steel) about “Mr. Wallace’s Line”: http://discovermagazine.com/1997/aug/mrwallacesline1198 http://theglyptodon.wordpress.com/2011/05/25/the-wallace-line/ http://evolution.berkeley.edu/evolibrary/article/history_16

An Example of Biogeographical Evidence: Galapagos Finches and Adaptive Radiation

Comparative Anatomy Evidence: Homologous Structures Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat

Comparative Anatomy Evidence: Vestigial Structures Boa pelvic region Human Coccyx (tailbone)

Comparative Embryology Evidence

Comparative Embryology Evidence Pharyngeal pouches Post-anal tail Chick embryo Human embryo

and snakes Lungfishes Amphibians Tetrapods Mammals Amniotes Fig. 13-6 Lungfishes 1 Amphibians Tetrapods 2 Mammals Tetrapod limbs Amniotes 3 Lizards and snakes Amnion 4 Crocodiles 5 Ostriches 6 Birds Feathers Hawks and other birds

Biochemical Evidence: amino acid sequence of hemoglobin

Biochemical Evidence: amino acid sequence of cytochrome c Note: These sequences use 1-letter amino acid codes. The “alignment” lines show where the amino acids are the same or different (+ or a blank). The + indicates a different amino acid but with the SAME R-group properties (nonpolar, polar or charged).

Amino Acids by R-group Properties with 3-letter and 1-letter abbreviations (pos. charged) (neg. charged) http://www.bio.miami.edu/dana/pix/aminoacids.gif

Biochemical Evidence: DNA sequence

Microevolution: a change in a population’s alleles over time How do we detect this change? Need to look at a population’s collection of alleles, or its gene pool. Darwin’s Finches video: http://www.hhmi.org/biointeractive/origin-species-beak-finch Rock Pocket Mouse video: http://www.hhmi.org/biointeractive/making-fittest-natural-selection-and-adaptation

Hardy-Weinberg Theorem H-W allows you to predict allele frequencies for a non-evolving population. For a population to be in H-W equilibrium, the following must be true: Population must be very large in size Population must be isolated from other pops (no gene flow: no immigration or emigration) No mutations Mating must be random No natural selection (equal chance of survival & reproductive success)

Hardy-Weinberg Theorem Allele frequencies p + q = 1 Genotype frequencies p2 + 2pq + q2 = 1 Dominant homozygotes Heterozygotes Recessive homozygotes Any changes to expected allele frequencies over time may indicate that micro-evolution is occurring in the population.

Phenotypes (fur color) Original population Evolved population Fig. 13-13 Original population Frequency of individuals Phenotypes (fur color) Original population Evolved population Stabilizing selection Directional selection Disruptive selection

Causes of Microevolution Genetic Drift Produces random changes to the gene pool of small breeding populations An allele may be eliminated from pop by chance Bottleneck Effect: dramatic decr in pop size due to environmental fluctuation (depletion of food supply, disease outbreak) Examples: Cheetahs, Florida Panthers Founder Effect: when one or a few individuals from a large pop establish a colony (new pop), and bring with them only a small fraction of genetic variation from orig pop Example: Marine Iguanas in Galapagos

Original population Bottlenecking event Surviving population Fig. 13-11a-3 Original population Bottlenecking event Surviving population

“By 1990s, the endangered Florida panther – a flagship species and one of the last remaining symbols of wilderness in Florida - was in serious trouble. There were fewer than 30 panthers remaining in the wild. The population suffered from several biomedical and morphological abnormalities, including low genetic diversity, heart defects, reproductive dysfunctions and kinked tails. Many of these problems were thought to be indicative of inbreeding, and conservation biologists recommended genetic restoration. This recommendation was controversial but was ultimately implemented after careful planning…” http://research.ifas.ufl.edu/featured-discoveries/genetic-restoration-saves-endangered-florida-panther#

Causes of Microevolution 2. Gene Flow movement of alleles by migration of individuals to a new population Generally increases variation within a population 3. Mutation Unpredictable change in DNA, a source of new alleles Introduces variation in pop Only inheritable if occurs in gametes Can be harmful, beneficial, or neutral 4. Natural Selection Leads to adaptive evol change, as “fittest” indiv survive to reproduce

Chromosome with allele conferring resistance to pesticide Fig. 13-3b Chromosome with allele conferring resistance to pesticide Pesticide application Survivors Additional applications will be less effective, and the frequency of resistant insects in the population will grow

Causes of Microevolution 5. Non-random Mating Inbreeding: Individuals mate more freq with closely related individuals Common in plants in the form of self-fertilization Not always harmful but sometimes leads to inbreeding depression (lower fitness: sterility, higher juvenile mortality) Examples: Cheetahs, Florida Panthers Sexual selection (mate selection): individuals select mates by their phenotype • Can change genotype frequencies Examples: Peacocks, Mallards, Humans, etc.

Fig. 13-14a

Microevolution change in allele frequencies in a population (a) (b) Fig. 13-UN4 Microevolution is the may result from change in allele frequencies in a population (a) (b) (c) random fluctuations more likely in a due to movement of due to leads to individuals or gametes adaptive evolution (d) (g) may be result of of individuals best adapted to environment (e) (f)