Transcript Chapter 21
Chapter 21 The Evidence for Evolution 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Beaks of Darwin’s Finches • Darwin collected 31 specimens from 3 islands in the Galápagos Islands – Darwin was not an expert on birds – Took them back to England for identification – Told his collection was a closely related group of distinct species – All were similar except for beak characteristics – In all, 14 species now recognized 2 http://people.rit.edu/rhrsbi/GalapagosPages/Pictures/LandBirds/FinchTypes.jpeg Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Woodpecker finch (Cactospiza pallida) Large ground finch (Geospiza magnirostris) Cactus finch (Geospiza scandens) Note the beak shape and how it relates to feeding style Warbler finch (Certhidea olivacea) Vegetarian tree finch (Platyspiza crassirostris) 3 • Finches eat a diversity of foods – Darwin hypothesized that different beak shapes were related to food gathering – Darwin wrote “… one might really fancy that … one [original] species has been taken and modified for different ends.” 4 http://www.pbs.org/wgbh/evolution/library/01/6/image_pop/l_016_02.html Modern research has verified Darwin’s selection hypothesis • 3 conditions necessary for natural selection – Phenotypic variation must exist in the population – This variation must lead to differences among individuals in differential lifetime reproductive success – Phenotypic variation among individuals must be genetically transmissible (heritability) to the next generation 5 http://evolution.berkeley.edu/evosite/evo101/images/mechan_intro.gif http://www.princeton.edu/main/images/news/2009/06/20090619_GrantP_RM_008-thumb.jpg Peter and Rosemary Grant • Studied medium ground finch on Daphne Major • Found beak depth variation among members of the population • Average beak depth changed from one year to the next in a predictable fashion 6 http://californiasislands.files.wordpress.com/2011/04/daphnemajor.jpg Peppered moths • When the environment changes, natural selection often favors different traits in a species • Adult peppered moth, Biston betularia, come in a range of shades – Body color is a single gene – Black individuals have the dominant allele • Black color was rare in the population until 1850s • From that time on, frequency increased to near 100% • WHY? 8 http://www.cals.ncsu.edu/course/ent425/tutorial/Ecology/survival.html • J.W. Tutt hypothesized that light-colored moths declined because of predation – Light moths were easily seen by birds on darkened (sooty) trees – Soot came from factories starting with Industrial Revolution – Confirmed with separate field studies with a variety of experimental designs 9 “Industrial” melanism • Phenomenon in which darker individuals come to predominate over lighter ones – Other moths in other industrialized areas showed same trend to darken – Pollution control resulted in bark color being lighter again – Light-colored peppered moths now are dominant in the population 10 Artificial Selection • Change initiated by humans • Favored individuals with certain phenotypic traits are bred, passing their genes on to the next generation • This directional selection should result in evolutionary change 11 https://sites.google.com/site/selectivebreedingofplants/ http://en.wikipedia.org/wiki/Drosophila_melanogaster • Experimental selection on Drosophila melanogaster (fruit fly) – Selected fruit flies with many bristles on abdomen – At the start, average number of bristles was 9.5 – Chose only those with most bristles to reproduce – 86 generations later, average number of bristles had quadrupled to nearly 40 12 http://bio.illinoisstate.edu/kaedwar/other/Sexing_Drosophila.shtml 13 http://leahlefler.hubpages.com/hub/How-Animals-Are-Domesticated-Domesticated-Foxes-Demonstrate-Genetic-Changes • Domestication may lead to unintentional selection for some traits – Attempt to domesticate silver foxes – Chose most docile animals only to breed – Within 40 years, had many of the same behavioral & physical traits as domestic dogs (curled tails, floppy ears, color) – Are traits for behavior linked to other traits? • Pleiotropy or linkage at work? 14 http://heatherlindayoung.wordpress.com/2011/01/19/the-one-with-the-waggley-tail/ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Teosinte Intermediates Modern corn • Agricultural selection – Differences have resulted from generations of human selection for desirable traits, such as greater milk production and larger corn ear size 15 Can selection produce major evolutionary changes? • Most scientists think that natural selection is the process responsible for most evolutionary changes documented in the fossil record • Some critics accept that selection can lead to changes within a species, but not the substantial changes documented in the fossil record – This argument does not fully appreciate the extent of change produced by artificial selection – Separate dog breeds would be species if found as fossils – All came from domestication of wolves 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Domestication – Human-imposed selection has produced a variety of cats, dogs, pigeons, grains and others – Breeds may have been developed for specific purposes • Dachshunds for badger pursuit Chihuahua Dachshund Wolf Greyhound Mastiff 17 Canid Domestication 18 http://www.csus.edu/indiv/l/loom/lect%2036s07.htm Fossil Evidence of Evolution • Fossils are the preserved remains of once-living organisms – The age of fossils can be estimated by comparing strata (relative dating) and by isotopic dating (determines absolute age) 19 http://pubs.usgs.gov/gip/fossils/numeric.html http://www.agiweb.org/news/evolution/figures/dating1.jpg Fossil Evidence of Evolution • Process of fossilization is rare event • Rock fossils are created when three events occur – Organism buried in sediment – Calcium in bone or other hard tissue mineralizes – Surrounding sediment hardens to form rock 20 http://jpostema.napsk12.org/blob/full/150186.gif Evolutionary transitions • Given the low likelihood of fossil preservation and recovery, it is not surprising that there are gaps in the fossil record • Many intermediate forms have been found • Oldest known bird fossil is Archaeopteryx 21 – Clearly intermediate between bird and dinosaur – Possesses some ancestral traits and some traits of present day birds http://universe-review.ca/I10-72-Archaeopteryx2.jpg 22 Archaeopteryx http://www.healthstones.com/dinosaurdata/a/archaeopteryx/archaeopteryx.html • Recent “transitional” discoveries – Four-legged aquatic mammal • Important link in the evolution of whales and dolphins from land-dwelling, hoofed ancestors 23 http://biologos.org/blog/evidences-for-evolution-part-2b-the-whales-tale Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Modern toothed whales Rodhocetus kasrani's reduced hind limbs could not have aided it in walking or swimming. Rodhocetus swam with an up-and-down motion, as do modern whales. 24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ambulocetus natans probably walked on land (as do modern sea lions) and swam by flexing its backbone and paddling with its hind limbs (as do modern otters). Pakicetus attocki lived on land, but its skull differed from that of its ancestors and exhibited many characteristics seen in whales today. 25 http://news.sciencemag.org/sciencenow/2011/02/scienceshot-snake-legsgoing-going.html • Recent “transitional” discoveries – Fossil snake with legs 26 • Recent “transitional” discoveries – Tiktaalik: a species that bridged the gap between fish and the first amphibian 27 http://scienceblogs.com/pharyngula/2006/04/05/tiktaalik-makes-another-gap/ • Horse evolution – Modern Equidae are all large, long-legged, fastrunning animals adapted to life on open grasslands – First horse was small with short legs • Wooded habitats – Path to modern horse involved… • Changes in body size • Toe reduction • Changes in tooth size and shape – Adaptations to climate change Early, overly • As grasslands became more widespread simplistic view • changed from browsers to grazers 28 Modified from http://www.tutorvista.com/content/biology/biology-ii/heredity-and-evolution/palaeontology.php Oligocene 30 MYA 45 MYA 50 MYA 55 MYA 60 MYA Hyracotherium (browsers) Orohippus Eocene Hyracotherium 40 MYA Epihippus 35 MYA Mesohippus (browsers) Mesohippus Anchitherium (browsers) Merychippus (mixed feeders) Neohipparion (grazers) Nannippus (grazers) – Rates of evolution have varied widely – Modern horse diversity is relatively limited – At peak of horse diversity there were 13 genera in North America alone Equus Dinohippus Onohippidion Astrohippus Pliohippus Calippus Protohippus Cormohipparion Nannippus Merychippus Parahippus Desmatippus Archaeohippus 25 MYA Miohippus 20 MYA Kalobatippus 15 MYA Hypohippus Miocene Anchitherium 10 MYA Megahippus 5 MYA Pseudhipparion browsers grazers mixed feeders Pliocene Hipparion Pleistocene Neohipparion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Equus (grazers) 29 Anatomical Evidence for Evolution • Homologous structures – Structures with different appearances and functions that are all derived from the same body part in a common ancestor – The bones in the forelimb of mammals are homologous structures – Different functions, same ancestor structure 30 • Early embryonic development – Strongest anatomical evidence supporting evolution comes from comparisons of how organisms develop – Embryos of different types of vertebrates, for example, often are similar early on, but become more different as they develop 32 http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/Recapitulation.html • Early embryonic development – Ex: early vertebrate embryos possess pharyngeal pouches that develop into • In humans: glands and ducts • In fish: gill slits 33 Color-coded pharyngeal arches and pouches indicate origin of same structure in fetus http://www.answersingenesis.org/articles/2007/03/14/fishy-gill-slits • Imperfections – some organisms do not appear perfectly adapted – Workable but imperfect solutions – Natural selection does not produce perfectly adapted structures • Selection acts on what is available • Produces “what works” • Environment constantly changing (“moving the bar”) 34 – Ex: most animals with long necks have many vertebrae for flexibility • Geese: 25 • Plesiosaurs: 76 • Mammals: 7 – But giraffes have 7 vertebrae, very large in size, to make up for the length of the neck Giraffe cervical vertebrae (neck bone) 35 http://www.boneclones.com/ http://fossil-chick.blogspot.com/2007_11_01_archive.html Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blind spot Vertebrate eye Photoreceptor cells Interneuron Molluscan eye Photopigment Nerve fibers Photoreceptor cells Light Light Photopigment Nerve impulse a. To brain via optic nerve Nerve fibers to brain b. – Example: eyes of vertebrates • Photoreceptors face backward – Nerve fibers slightly obscure light and create a blind spot – Mollusks’ eyes are more optimally designed with no obstruction or blind spot 36 • Vestigial structures – Have no apparent function, but resemble structures their ancestors possessed • Human ear wiggling muscles, tail bone (coccyx) • Hip bones in boa constrictors 37 http://science.halleyhosting.com/sci/ibbio/ecology/notes/natselect/evidence.htm http://explosionsoflife.tumblr.com/post/22639983292/ichthyologist -antarctic-ice-fish http://jeb.biologists.org/content/209/10/1791/F1.expansion.html Antarctic fish lacks RBCs and a functional hemoglobin gene, but still has remnants of mutated gene. Blood from typical fish with hemoglobin (right) and Antarctic fish (left) • Vestigial structures – Genetic relicts fossil genes (pseudogenes) • Nonfunctional genes are retained, but mutated • Example is hemoglobin gene in Antarctic fishes – Oxygen content is so high in cold waters that they don’t need hemoglobin to carry oxygen, blood is colorless – However, mutated hemoglobin gene is still found in their DNA http://science.halleyhosting.com/sci/ibbio/ecology/notes/natselect/evidence.htm 38 Biogeography • Study of the geographic distribution of species • Reveals that different geographical areas sometimes exhibit groups of plants and animals of strikingly similar appearance, even though the organisms may be only distantly related • Natural selection appears to have favored parallel evolutionary adaptations in similar environments Note the similar forms of unrelated ant-eating mammals, an example of convergence of form 39 http://www.pbs.org/wgbh/evolution/library/01/4/image_pop/l_014_01.html Convergent evolution • Similar forms having evolved in different, isolated areas because of similar selective pressures in similar environments • Marsupial and placental mammals – Only marsupials found in Australia – Australian marsupials resemble placental mammals on other continents 40 http://carolguze.com/text/102-15-evolution1.shtml Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Niche Placental Mammals Burrower Anteater Mole Nocturnal Insectivore Climber Glider Stalking Predator Chasing Predator Flying squirrel Grasshopper mouse Wolf Australian Marsupials Ocelot Ring-tailed lemur Lesser anteater Numbat Thylacine Spotted cuscus Marsupial mole Marsupial mouse Flying phalanger Tasmanian quoll 41 • Convergence among fast-moving marine predators – Hydrodynamics of moving through water require a streamlined body shape to minimize friction – Sharks, tuna, icthyosaurs, and dolphins 42 Biogeographical studies • Darwin noted on his voyage that – Islands are often missing plants & animals common on continents • Can live there if introduced – Species present on islands often diverged from continental relatives • Occupy niches used by other species on continents • Island species usually are more closely related to species on nearby continents http://squamates.blogspot.com/2011/01/attempt-to-reduceinvasive-predators-in.html Adult Key deer in the Florida Keys are smaller than whitetail deer 43 • Darwin concluded: – Many islands have never been connected to the mainland – Species arrive on islands by dispersing across the water – Dispersal from nearby areas is more likely than distant sources – Species that can fly, float or swim are more likely to inhabit islands – Colonizers often evolve into many species 44 http://www.guardian.co.uk/science/punctuated-equilibrium/2011/nov/02/hawaiian-honeycreepers-tangled-evolutionary-tree Darwin’s critics • Evolution and natural selection are nearly universally accepted by biologists • Source of controversy for some in the general public • Seven principle objections 1. Evolution is not solidly demonstrated • “Just a theory” • In science, theories have a lot of supporting evidence • Theories of gravity, relativity, plate tectonics, evolution 45 Darwin’s critics 2. There are no fossil intermediates • Actually many intermediates have been found since Darwin’s time • See examples above & http://www.talkorigins.org/indexcc/CC/CC200.html 3. The intelligent design argument • Too complex for a random process • Natural selection is not random but it is not directed • Vestigial structures refute an “intelligent designer” 46 Darwin’s critics 4. Evolution violates Second Law of Thermodynamics • Things become more disorganized • Earth is not a closed system and energy is constantly added from the Sun • Biology does have organization 5. Proteins are too improbable • Probability of hemoglobin as random event = (1/20)141 • Can’t argue backwards – what are the odds of students having the birthdates they do in class – Statistics might predict the likelihood of having another class with the same birthdays (looking forward) 47 Darwin’s critics 6. Natural selection does not account for major evolutionary changes • • • • No scientist has evolved a fish into a frog Artificial selection has produced differences more distinctive than those between wild species Fossil transitions, over millions of years, is strong evidence that small changes accumulate Evolutionary development (“evodevo”) studies show changes to a few regulatory genes can have major impact on body form 48 Darwin’s critics 7. The irreducible complexity argument • Intricate machinery of cell cannot be explained by evolution from simpler stages • Natural selection can act on a complex system because at every stage of its evolution, the system functions • Parts are added to enhance function, some may be lost in the process…but still a product of selection over long periods of time • With careful study, the pathway of complex structures may be found 49