Evidence of Evolution by Natural Selection Chapter 21. Evidence of Evolution by Natural Selection Dodo bird

Evolution is "so overwhelmingly established that it has become irrational to call it a theory." Born in 1904 in Germany, Mayr trained as a medical student but realized he had a greater passion for studying birds and biology. Emigrating to the United States, he became a curator at the American Museum of Natural History, working on bird classification while formulating his key ideas about evolution. In 1942 he published his most important work, Systematics and the Origin of Species. Mayr moved to Harvard University in 1953 and served as director of the school's Museum of Comparative Zoology from 1961 to 1970. Since then, he has published a number of books and chapters and received the prestigious Japan Prize for Biology in 1983. In his landmark 1942 book, Mayr proposed that Darwin's theory of natural selection could explain all of evolution, including why genes evolve at the molecular level. On the stubborn question of how species originate, Mayr proposed that when a population of organisms becomes separated from the main group by time or geography, they eventually evolve different traits and can no longer interbreed. It's this isolation or separation that creates new species, said Mayr. The traits that evolve during the period of isolation are called "isolating mechanisms," and they discourage the two populations from interbreeding. Moreover, Mayr declared that the development of many new species is what leads to evolutionary progress. "Without speciation, there would be no diversification of the organic world, no adaptive radiation, and very little evolutionary progress. The species, then, is the keystone of evolution." -- Ernst Mayr What Evolution Is 2001 Professor Emeritus, Evolutionary Biology Harvard University (1904-2005)

Support for Darwin’s ideas _______________ change over time ___________________ Homologous structures Analogous structures embryology _________________ measure of common ancestry ________________ induced evolution Fossil Record Comparative Anatomy Molecular Analysis Artificial Selection

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

Formation of sedimentary strata containing fossils 1 Rivers carry sediment to the ocean. Sedimentary rock layers containing fossils form on the ocean floor. 2 Over time, new strata are deposited, containing fossils from each time period. 3 As sea levels change and the seafloor is pushed upward, sedimentary rocks are exposed. Erosion reveals strata and fossils. Younger stratum with more recent fossils Older stratum with older fossils

A gallery of fossil types (a) Dinosaur bones being excavated from sandstone (g) Tusks of a 23,000-year-old mammoth, frozen whole in Siberian ice (e) Boy standing in a 150-million-year-old dinosaur track in Colorado (d) Casts of ammonites, about 375 million years old (f) Insects preserved whole in amber (b) Petrified tree in Arizona, about 190 million years old (c) Leaf fossil, about 40 million years old

Fossil record Today’s organisms descended from ancestral species Support for a very old earth

A dragonfly fossil from Brazil, more than 100 million years old

Evolution of birds Archaeopteryx lived about 150 mya links reptiles & birds The avian nature of the brain and inner ear of Archaeopteryx (Alonso et al. 2004) - Archaeopteryx, the earliest known flying bird from the Late Jurassic period, exhibits many shared primitive characters with more basal coelurosaurian dinosaurs (the clade including all theropods more bird-like than Allosaurus), such as teeth, a long bony tail and pinnate feathers. However, Archaeopteryx possessed asymmetrical flight feathers on its wings and tail, together with a wing feather arrangement shared with modern birds. This suggests some degree of powered flight capability but, until now, little was understood about the extent to which its brain and special senses were adapted for flight. Alonso et al. (2004) investigated this problem by computed tomography scanning and three-dimensional reconstruction of the braincase of the London specimen of Archaeopteryx. A reconstruction of the braincase and endocasts of the brain and inner ear suggest that Archaeopteryx closely resembled modern birds in the dominance of the sense of vision and in the possession of expanded auditory and spatial sensory perception in the ear. Alonso et al. (2004) concluded that Archaeopteryx had acquired the derived neurological and structural adaptations necessary for flight. An enlarged forebrain suggests that it had also developed enhanced somatosensory integration with these special senses demanded by a lifestyle involving flying ability. Smithsonian Museum, Washington, DC 10

Evolutionary Change in Horses

Where are the Intermediates? Land Mammal ? Where are the Intermediates? There are innumerable intermediate & transitional forms Wales as land creatures returning to other water…. Where are the intermediate forms of whale ancestors? Cartoon making fun of this idea. The cartoons disappeared 10-12 years when this fossil was found. Ambilocetic natans = “Walking whale who likes to swim” 4-5 intermediate forms all found in last 2 decades Indus River valley in between India & Pakistan.

A transitional fossil linking past and present Oh. Here they Are!

2006 Fossil Discovery of Early Tetrapod Tiktaalik “missing link” from sea to land animals 14

Burgess Shale

Burgess Shale British Columbia 505 million years ago (Cambrian Explosion) Period when animals rapidly diversified in body plan/anatomical feature _________________ Taphonomic window

Anatomical record Homologous structures similarities in characteristics resulting from _______________ common ancestry 23

Homologous structures Similar _________ Similar ____________ Different _________ Evidence of close evolutionary relationship _______ common ancestor structure development functions recent 24

Homologous structures spines leaves succulent leaves tendrils needles colored leaves 25

Don’t be fooled by their looks! Analogous structures Separate evolution of structures similar ____________ similar ________________ _____________ internal structure & development different_________ no ______________________ structure external form different origin evolutionary relationship Don’t be fooled by their looks! Solving a similar problem with a similar solution 26

Analogous structures 3 groups with wings flight evolved 3 separate times = evolving similar solutions to similar “problems” Analogous structures 3 groups with wings does this mean they have a recent common ancestor?

& sleek bodies are analogous structures! Convergent evolution Fish: aquatic vertebrates Dolphins: aquatic mammals similar adaptations to life in ______ environments not closely related similar Those fins & tails & sleek bodies are analogous structures! 28

Parallel Evolution marsupial mammals placental mammals Convergent evolution in common niches Similar ecological roles in ________environments, Similar adaptations were selected but are not closely related different marsupial mammals placental mammals 29

Convergent evolution of analogous burrowing characteristics marsupial mole placental mole

Parallel types across continents Niche Placental Mammals Australian Marsupials Burrower Mole Anteater Mouse Lemur Flying squirrel Ocelot Wolf Tasmanian “wolf” Tasmanian cat Sugar glider Spotted cuscus Numbat Marsupial mole Marsupial mouse Nocturnal insectivore Climber Glider Stalking predator Chasing 31

Vestigial organs Structures that serve _________________ 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 little or no functions 32

Vestigial organs Hind leg bones on whale fossils Why would whales have pelvis & leg bones if they were always sea creatures? 33

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. 34

Anatomical similarities in vertebrate embryos Pharyngeal pouches Post-anal tail Chick embryo Human embryo

Why compare these genes? Molecular record Comparing DNA & protein structure universal genetic code! DNA & RNA compare common genes cytochrome C (respiration) hemoglobin (gas exchange) Why compare these genes? 25 50 75 100 125 Millions of years ago Horse/ donkey Sheep/ goat Goat/cow Llama/ cow Pig/ Rabbit/ rodent Horse/cow Human/rodent Dog/ Human/ Human/kangaroo Nucleotide substitutions Closely related species have sequences that are more similar than distantly related species A molecular record of evolutionary relationships 36

Comparison of a protein found in diverse vertebrates Species Human Rhesus monkey Mouse Chicken Frog Lamprey 14% 54% 69% 87% 95% 100% Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide

Comparative hemoglobin structure Human Macaque Dog Bird Frog Lamprey Why does comparing amino acid sequence measure evolutionary relationships? 8 32 45 67 125 10 20 30 40 50 60 70 80 90 100 110 120 Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans 38

Building “family” trees Closely related species (branches) share same line of descent until their divergence from a common ancestor 39

“descendants” of wild mustard “descendants” of the wolf Artificial selection Artificial breeding can use variations in populations to create vastly different “________” & “__________” breeds varieties “descendants” of wild mustard “descendants” of the wolf 40

It’s Important To Remember How Powerful And Fast Selection Can Be!!!

Natural selection in action Insecticide & drug resistance insecticide doesn’t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective The evolution of resistance to insecticides in hundreds of insect species is a classic example of natural selection in action. The results of application of new insecticide are typically encouraging, killing 99% of the insects. However, the effectiveness of the insecticide becomes less effective in subsequent applications. The few survivors from the early applications of the insecticide are those insects with genes that enable them to resist the chemical attack. Only these resistant individuals reproduce, passing on their resistance to their offspring. In each generation the % of insecticide-resistant individuals increases. 42

Evolution of drug resistance in HIV Patient No. 1 Patient No. 2 Patient No. 3 Percent of HIV resistant to 3TC Weeks

Evolution Misconceptions A Brief Discussion

Evolution is not goal-oriented An evolutionary trend does not mean that evolution is goal-oriented. Surviving species do not represent the peak of perfection. There is compromise & random chance involved as well Remember that for humans as well! Evolution is not the survival of the fittest. Rather it is the survival of the just good enough. 45

"Nothing in biology makes sense except in the light of evolution." Theodosius Dobzhansky: Integrating Genetics and Evolution Theodosius Dobzhansky, a Russian geneticist who moved to the United States, provided laboratory evidence for natural selection and variation where previously there had been only field observation. Dobzhansky's work with Drosophila, or fruit flies, provided new evidence that supported Darwin's theory that natural selection, acting on genetic variation in populations, is a driving force in evolution. -- Theodosius Dobzhansky March 1973 Geneticist, Columbia University (1900-1975) 46

I might be dead, but Perhaps you children would appreciate a bit of what you call the “rap” music?!?

Just Because Things Seem Obvious Doesn’t Mean They Don’t Need To Be Supported

Peppered Moths Dark vs. light variants Year % dark % light 1848 5 95 1848 5 95 1895 98 2 1995 19 81 49

Peppered moth What was the selection factor? early 1800s = pre-industrial England low pollution lichen growing on trees = light colored bark late 1800s = industrial England factories = soot coated trees killed lichen = dark colored bark mid 1900s = pollution controls clean air laws return of lichen = light colored bark industrial melanism 50

Genome sequencing What can whole genome sequence data tell us about evolution of humans?

Primate Common Ancestry? Chromosome Number in the Great Apes (Hominidae) orangutan (Pogo) 48 gorilla (Gorilla) 48 chimpanzee (Pan) 48 human (Homo) 46 Could we have just lost a pair of chromosomes? Hypothesis: Change in chromosome number? If these organisms share a common ancestor, then is there evidence in the genome for this change in chromosome number

Chromosomal fusion Testable prediction: If common ancestor had 48 chromosomes (24 pairs), then humans carry a fused chromosome (23 pairs). Ancestral Chromosomes Fusion Homo sapiens Chromosome Number in the Great Apes (Hominidae) orangutan (Pogo) 48 gorilla (Gorilla) 48 chimpanzee (Pan) 48 human (Homo) 46 Inactivated centromere Telomere sequences Testable! This is what makes evolution science & not belief! Centromere Telomere

Test of the Human Genome Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731. Ancestral Chromosomes “Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1, where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22. During the formation of human chromosome 2, one of the two centromeres became inactivated (2q21, which corresponds to the centromere from chimp chromosome 13) and the centromeric structure quickly deterioriated.” Fusion Homo sapiens Inactivated centromere Telomere sequences Well I’ll be a monkey’s …or an ape’s… uncle! Chr 2 Human Chromosome #2 shows the exact point at which this fusion took place

Geographic variation in chromosomal mutations 1 2.4 3.14 5.18 6 7.15 XX 19 13.17 10.16 9.12 8.11 2.19 3.8 4.16 5.14 6.7 15.18 11.12 9.10

Unity & Diversity Only evolution explains both the unity & diversity of life By attributing the diversity of life to natural causes rather than to supernatural creation, Darwin gave biology a strong, scientific, testable foundation

Any Questions?? 2007-2008 57

1. A complete fossil record Exists because of the great preservation in ocean sediment Exists because of the solidification of minerals around organisms Is available because of the small location in which all organisms used to live Exists because organisms that die become embedded in the soil to form rocks Does not exist

2. The similarity of insect wings and bird wings is an example of Behavioral adaptations Geographic isolation Adaptive radiation Convergent evolution Divergent evolution

3. The human appendix is an example of A balanced polymorphism Divergent evolution Convergent evolution A vestigial structure A homologous structure

One piece of evidence that supports evolution from molecular biology is: carbohydrate structure amino acid sequence lipid composition nucleotide structure cellulose chains

Any Questions?? share a common ancestor with apes? This has the potential of contradicting evolution There are genetic similarities between humans & apes But humans have 2 fewer chromosomes (24 pairs vs. 24 pairs) Where’s the missing chromosome? can’t lose it = lethal Must have been a fusing. So should be able to look at our genome & find the fusing. If we don’t find it then evolution is wrong. Nifty little markers = centromeres & telomeres. Fusing would put telomeres in the middle of a chromosomes. If we don’t find this then evolution is wrong. Chr #2 was formed by head to head fusion of 2 primate chromosomes The centromere that has been inactivated corresponds to chimp chromosome #13