Evidence of Evolution by Natural Selection Chapter 19 Evidence of Evolution by Natural Selection 2006-2007 Dodo bird

THINK: Make a list of all the vestigial structures you can think of. Why do they exist?

Vestigial organs Modern animals may have structures that serve little or no function remnants of structures that were functional in ancestral species evidence of change over time some snakes & whales show remains of the pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone

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

Comparative embryology Similar embryological development in closely related species all vertebrate embryos have a gill pouch at one stage of development fish, frog, snake, birds, human, etc.

Molecular record Comparing DNA & protein structure universal genetic code! DNA & RNA cytochrome C (respiration) protein structure hemoglobin (gas exchange) Evolutionary relationships among species are documented in their DNA & proteins. Closely related species have sequences that are more similar than distantly related species.

Comparative hemoglobin structure Human Macaque Dog Bird Frog Lamprey 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

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

VIEW: http://www. pbs. org/wgbh/evolution/library/07/3/real/l_073_47

What data from whole genome sequencing can tell us about evolution of humans

Example: Evolutionary Hypothesis of Common Ancestry Chromosome Numbers in the great apes: human (Homo) 46 chimpanzee (Pan) 48 gorilla (Gorilla) 48 orangutan (Pogo) 48 Do we 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 Change in chromosome number? If these organisms share a common ancestor, then is there evidence in the genome for this change in chromosome number

Chromosome Numbers in the great apes (Hominidae): Ancestral Chromosomes Chromosome Numbers in the great apes (Hominidae): human (Homo) 46 chimpanzee (Pan) 48 gorilla (Gorilla) 48 orangutan (Pogo) 48 Fusion Homo sapiens Inactivated centromere Telomere sequences Centromere Telomere Do we share a common ancestor with apes? 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. Testable prediction: If common ancestor had 48 chromosomes (24 pairs) then humans carry a fused chromosome; or If common ancestor had 46 chromosomes (23 pairs) then apes carry a split chromosome.

Inactivated centromere Human Chromosome #2 shows the exact point at which this fusion took place “Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two acrocentric chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1 (ref. 2; hg 16:114455823 – 114455838), where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22 (Fig. 3; Supplementary Fig. 3a, region A). 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 (42).” Homo sapiens Inactivated centromere Telomere sequences Do we share a common ancestor with apes? Chr #2 was formed by head to head fusion of 2 primate chromosomes The centromere that has been inactivated corresponds to chimp chromosome #13 Chr 2 Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731.

In case you had any doubts…

“descendants” of wild mustard “descendants” of the wolf Artificial selection Artificial breeding can use differences between individuals to create vastly different “breeds” & “varieties” “descendants” of wild mustard “descendants” of the wolf

THINK: You’ve heard about MRSA? Methicillin Resistant Staphlococcus aureus. Based on what you know about how natural selection happens, how might Staph infections (caused by a bacterium, S. aureus) become resistant to the antibiotics we use to kill them?

Natural selection in action Insecticide & drug resistance insecticide didn’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. See: http://www.pbs.org/wgbh/evolution/library/11/2/e_s_6.html

Evolution of Drosophila All of the 500+ endemic species of Drosophila in Hawaiian archipelago descended from common ancestor that reached Kauai over 5 million years ago

Witness to Evolution Peppered Moth dark vs. light variants

Peppered moth Year % dark % light 1848 5 95 1895 98 2 1995 19 81

Peppered moth Why did the population change? 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

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?? 2006-2007

Older sediments are below younger sediments. Study of Paleontology Older sediments are below younger sediments. Georges Cuvier (1769-1832)

Gradualism James Hutton (1726-1797) Earth’s geologic features — profound change formed as product of slow but continuous & cumulative processes

Uniformitarianism Charles Lyell (1797-1875) geologic processes have not changed throughout Earth’s history Conclusion: Earth must be much older than 6,000 years

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