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ANTH/BIOL/GEOL/HIST/ PHIL 225 Class 13, Feb 22 Natural selection and adaptation Prof. Beall for Prof. Princehouse Dr. Princehouse will hold extra office hours Wednesday 3-4 pm. Materials you have read or seen: •Futuyama on natural selection and adaptation •Video on natural selection •Video on sexual selection •Spandrels article (?Spaniels article) Materials you have brought to class: 3 written questions on the readings EVOLUTION • The process of biological change through time. • The mechanism is natural selection. • The outcome is organisms adapted to their environments. Evolution by natural selection has three essential elements. Organisms have reproductive capacity that is rarely fulfilled because environmental resources are limited. Organisms vary in their ability to survive and reproduce. Variation is heritable. EVOLUTION BY NATURAL SELECTION: 3 postulates 1. Species are capable of producing offspring faster than their resources can support Some estimate there were 3-5 billion passenger pigeons in North America when Europeans first arrived. The last one died in 1914. Old magazine illustration of hunters shooting Passenger Pigeons. Note the density of the flight. During migration, flocks could be 1 mile wide and 300 miles long, taking several hours to pass. http://www.stanford.edu/group/stanfordbirds/text/essays/essaypix/Passenger_Pigeon.gif https://www.geology.ucdavis.edu/iype/sept/passengerpigeon.jpg EVOLUTION BY NATURAL SELECTION: 3 postulates 2. Variation among organisms affects their ability to survive and reproduce in their environment “Any minute variation in structure, habits or instincts adapting that individual to the new conditions would tell upon its vigour and health” (C. Darwin, 1858, p. ) http://www.pbs.org/safarchive/images/img_5cool/galapagos/finches.gif http://home.comcast.net/~mkent595/Micro10.JPEG http://www.anth.ucsb.edu/faculty/walker/classes/anth105/index_files/image002.jpg Variation is abundant. http://www.newscientist.com/data/images/ns/cms/mg20427342.500/mg20427342.500-1_300.jpghttp://images.mirror.co.uk/upl/m4/aug2009/6/1/baboon-2957207.jpg http://learn.genetics.utah.edu/content/begin/traits/images/hand_clasp.jpg EVOLUTION BY NATURAL SELECTION: 3 postulates 3. Variations are heritable Variations are heritable. Hitch-hiker’s thumb is a recessive trait. Non-roller is a recessive trait. Height is influenced by heredity and environment. http://www.newscientist.com/data/images/ns/cms/mg20427342.500/mg20427342.500-1_300.jpghttp://images.mirror.co.uk/upl/m4/aug2009/6/1/baboon-2957207.jpg http://learn.genetics.utah.edu/content/begin/traits/images/hand_clasp.jpg Galapagos finch species depicted here have all arisen from a common ancestor, but have evolved a remarkable diversity of beak shapes and sizes as they have adapted to exploit different food sources Depth and breadth of beaks controlled by calmodulin locus. Length of beaks controlled by BMP4 locus. The outcome of evolution by natural selection • Species are well adapted to their environment • Tremendous variety of species • Tremendous variety of organisms Well adapted organisms are the outcome of evolution by natural selection • Organisms with variants that make them better able to survive contribute disproportionately to the next generation • Over time, what happens? – Descendent organisms have different features, structures, behaviors than their ancestors. – Environmental inevitably changes. Adaptations are the features that improve survival. • Adaptations work. • Adaptations are not perfect. • The process is called natural selection, not natural perfection. • New features of organisms result from natural selection The Antarctic ice fish has several new features. It is related to the mackerel. Mackerel is like the ancestor fish. http://www.glaucus.org.uk/Mackerel.jpg Ice fish is descended from its ancestor with more modifications. http://www.underwatertimes.com/news.php?article_id=632194710 The ice fish have adapted to low ambient temperature and have low body temperature. • Icefish are pale because they do not make hemoglobin and don’t have red blood cells. They have ‘ice water’ in their veins. • Icefish are pale because they don’t make myoglobin. The Antarctic ice fish has no red blood cells, no hemoglobin, and no myoglobin. • • • • How can they survive? They adsorb oxygen from the water. How did this come about? Water temperature dropped from about 68 ºF to < º30 F in the past 55 million years. The genetic fossil record reveals the changes that caused the loss of hemoglobin and myglobin. • One hemoglobin gene is nonfunctional and one is just gone. • Myoglobin gene is non-functional. • We can see the remnants of these genes. They have ‘gone extinct’. Genetic changes resulted in the addition of antifreeze proteins in veins. • Antifreeze proteins are necessary to prevent freezing solid. • These antifreeze genes arose from a part of a gene that originally encoded a digestive enzyme. • Part of that enzyme broke off and relocated to another place in the fish genome, replicated, and now makes antifreeze. Icefish adaptations are examples of chance, necessity and tinkering. • • • • Improvised series of steps. Destruction of some old genetic code Tinkering with some code to make new genetic code. Icefish evolved from a warm-water, hemoglobindependent lifestyle to a very-cold-water, oxygen adsorbing, antifreeze-making lifestyle. Coat color of rock pocket mouse is another example of descent with modification that has occurred in many species. MC1R gene has two alleles. Two copies of light allele results in sandy color of mice. MC1R allele in humans and our ancestors accounts for blonde and red hair in modern humans and our ancestors including Neanderthals. Galapagos finch species depicted here have all arisen from a common ancestor, but have evolved a remarkable diversity of beak shapes and sizes as they have adapted to exploit different food sources Depth and breadth of beaks controlled by calmodulin locus. Length of beaks controlled by BMP4 locus. High-altitude natives are a natural experiment of adaptation to an extreme, lifelong stress: hypoxia. 100 %Sea Level PiO2 140 90 80 120 70 100 60 Inspired O2 , mmHg 80 50 60 40 0 1000 2000 3000 4000 Altitude, m 5000 6000 7000 % Sea Level PiO2 Inspired O2, mmHg 160 •Hypoxia is severe and unavoidable. •All residents at a given altitude are exposed to the same ambient stress. •All steps in the process of oxygen delivery are affected. The Tibet Plateau has an average altitude of 15,000’ and is about 1500 x 600 miles in extent and is extremely stressful. Qinghai Ladakh Qinghai-Tibet Plateau Phala Lhasa Shigatse India Nepal NASA image Phala’s is at 15,200-17,500’ altitude; Shigatse is at 13,000’. Hemoglobin carries less oxygen at high altitudes. • Altitude % Oxygen saturation Cleveland 98% Pike’s Peak 80% . Tibetans have genotypes for high or low oxygen saturation of hemoglobin. AA SAT=80 ++ 1% BB SAT=90 AB SAT=89 AB SAT=89 Altitude, Tibetans % Oxygen Saturation 4200m BB genotype 88% 4200m AA genotype 78% AA SAT=80 http://www.pennhealth.com/health_info/images/19443.jpg Women estimated to have genotypes for high oxygen saturation have more living children. Estimated Genotype Genotypic Means # Pregnancies/ livebirths # Living Children # Infant Deaths Low O2 Sat (AA) 4.6/4.5 1.6 1.7 High O2 Sat (AB) 4.9/4.8 3.6 0.6 High O2 Sat (BB) 4.8/4.6 3.8 0.3 The outcome of evolution by natural selection is organisms adapted to their environments. An adaptation is a characteristic that increases an organism’s chance of survival and reproduction. How do we identify adaptations? St. Mark’s Cathedral, Venice The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme STEPHEN JAY GOULD AND RICHARD C. LEWONTIN http://www.aaas.org/spp/dser/evolution/history/spandrel Spandrels of San Marco, Venice http://www.jssgallery.org/Essay/Venice/San_Marco/Basilica_San_Marco/Basilica_San_Marco_interior.htm Adaptationist Program, I • Why does this trait exist? • What is the function of a given structure or organ? • How has this trait contributed to reproductive success? • What is the evolutionary history of the feature? • Is the trait part of some other adaptive machinery? Adaptationist Program, II • Develop a functional hypothesis • Develop a test or tests of that hypothesis • Predict other, unknown, aspects of human biology and test those hypotheses, too There are potential pitfalls. • It is necessary to demonstrate the operation of natural selection rather than to assume it. • Current function may not explain why a trait evolved. • If we start with the wrong trait, we get the wrong explanation. http://australianmuseum.net.au/Uploads/Images/9667/DSC_0027_big.jpg The Spaniels of St. Marx and the Panglossian Paradox: A Critique of a Rhetorical Program http://www.honeybet.co.uk/photos/doggroupweb.jpg