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Evolution Lectures 2005 Modified 2008 M.Elizabeth Evolutionary Evidence • Comparative anatomy - living things are • • • constructed along the same lines Taxonomy - life is hierarchical (“tree of life”) Geology - Earth is ancient, fossils record evolution, small changes can have big effects Biogeography - same environment yields different organisms Definition: Evolution • 'Evolution' is a description of AND an explanation of the history of species their origins, how they change, survive, become extinct. • So evolution concerns BOTH a historical account of life on earth AND an attempt to explain how observed changes have happened. • Defined as the slow change of organisms over time and a change in the frequency of certain alleles in the population. Overview of Lecture Evidence that evolution has occurred •Comparative anatomy •Taxonomy •Geology and fossils •Biogeography How does evolution occur? •Malthus and natural selection •How does “perfection” arise? •How does novelty arise? A changing world view (200-300 years ago) Earth is young In the 17th century Archbishop James Ussher used the Bible to date the origin of the earth as 4004 B.C. (Vice-chancellor of Cambridge refined this to the morning of Sunday, October 23rd, 4004 B.C.) Fixity of species Species are permanent, natural kinds. They do not change. A fixed plan of creation. Design Living things seem designed for a purpose, and a design implies a designer A changing world view Earth is ancient Approximately 4,500,000,000 years old (radioactive isotopes) Species evolve Living things are constantly changing, new species arise and others go extinct The history of life is contingent Adaptation Fit between organisms and their environment is due to natural selection (“blind watchmaker”) Organisms are often imperfectly created Darwin’s place in science Unity How we are the same and yet different All living organisms contain four macromolecules –carbohydrates –lipids –proteins –nucleic acids Life is constructed on a similar plan Human and chimpanzee facial expressions Human and chimpanzee chromosomes Life is constructed on a similar plan – homologous structures. Vestigial organs The eye bulbs of blind, cavedwelling creatures, such as the grotto salamander (Typhlotriton spelaeus). The anthers and pollen of asexual dandelions. Vestigial organs in humans Appendix Nictating membrane in eye What is Embryology? • Embryology is the study development of the embryo. • An embryo is the young animal undergoing development within the egg or womb. • Embryology is used to illustrate common ancestry because there are similarities between organisms' embryological development. Hind limbs in whales Whale embryo Modern whale Fossil whale Human embryo at 5 weeks Similarities during embryonic development 7 properties of life 1.Ordered structure 2.Reproduction 3.Growth and development 4.Energy utilization 5.Response to environment 6.Homeostasis 7.Evolutionary adaptation • How do we recognise evolution? • What causes evolution? • Does evolution lead to perfection? What is evolution? Decent with modification What is evolution? Time t+x Time t Low High Trait value We can redefine evolution as a change over time • How do we recognise evolution? • What causes evolution? • Does evolution lead to perfection? Causes of Evolution There are 5 causes ‘The accidental toolkit’: • Natural selection • Genetic drift • Mutation • Gene flow • Nonrandom mating Causes of Evolution 1. Natural Selection There are 3 important points: • Variation • Differential success Causes of Evolution 1. Natural Selection There are 3 important points: • Variation • Differential success • Inheritance Over time there will be mainly white individuals Causes of Evolution 1. Natural Selection Differences in reproductive success Fitness - relative contribution to the next generation • survival • access to mates • breeding success Causes of Evolution 1. Natural Selection Example: the peppered moth Coloration is a camouflage: Causes of Evolution 1. Natural Selection % black form Example of the industrial melanism of the peppered moth 1800 1900 2000 Causes of Evolution 2. Genetic Drift Random changes in the frequency of traits to chance factors Occurs under 2 conditions: founder effect bottleneck effect Causes of Evolution 2. Genetic Drift Founder effect - when a new population is a small sample of a large population Example: Porphyria 1 / 80,000 King George III 1 / 8,000 Causes of Evolution 2. Genetic Drift Bottleneck effect - when only a small fraction of the population survives that is no longer representative Example: Lions living in the Ngorogoro 100 Before crash 50 1960 1975 1990 RARE Causes of Evolution 2. Genetic Drift Bottleneck effect - when only a small fraction of the population survives that is no longer representative Example: Lions living in the Ngorogoro 100 After crash 50 1960 1975 1990 COMMON Causes of Evolution 3. Mutation Changes in an organism’s DNA Hopeful monsters Probably of little importance Causes of Evolution 4. Gene Flow Changes due to movement from one place to another 20% RED + 2 REDS 27% RED Causes of Evolution 5. Nonrandom Mating Individuals with particular traits are more likely to mate Sexual Selection Boys fight Boys look fetching Causes of Evolution 5. Nonrandom Mating Boys fight - inter-sexual competition The winner will mate Causes of Evolution 5. Nonrandom Mating Boys look fetching - intra-sexual competition The male with the best ornament will be chosen • How do we recognise evolution? • What causes evolution? • Does evolution lead to perfection? Does Evolution lead to Perfection Does the ability to perform improve? - ADAPTATION Just-so-stories The elephant’s child Does Evolution lead to Perfection Foraging efficiency How do we know there is an ADAPTATION? Bill size Adaptation happens only by selection, all other changes are like a lottery Does Evolution lead to Perfection The course of evolution depends on: • Existing variation • Historical constraints • Compromise • ‘Accidental toolkit’ The Tale of the Monkey T HE H OR I G I N BF BV OF S P E C I E S GDE F J F T KNHL OE A The Tale of the Monkey T HE OR I G I N OF S P E C I E S H BF BV GDE F J F T KNHL OE A YHXGO KGE NBAF NCL E C I E Z B H E O H I G I N O F C S ME C I E S 1 10 20 Natural Selection Edits Variation Evolution is not the work of a designer, but the work of a tinkerer. Variation is the fuel of evolution - next Natural Selection: If variation of a trait within a population has a genetic basis, and some variants have greater survival and reproduction, then, over time, the favored trait will predominate in the population. Requirements: C Variation in a trait within a population. (Giraffe's necks) C More individuals are born each generation than can survive: the "Struggle for Existence" C Giraffes with longer necks get better food, have more babies (have an advantage in the struggle for existence) C Longer necks beget longer necks (variation is heritable) Results: Over time, average neck length increases Under other conditions, over longer periods of time, new species form (e.g. the Okapi) Evolution as a result of chance events (e.g. Dinosaurs!) Role of chance in evolution: Extinctions Catastrophic Event • Cretaceous-Tertiary (KT) transition: • – Dinosaurs disappear “instantaneously” 65 myr ago Meteorite event – Luis and Walter Alvarez: transition rich in iridium (Ir), like in meteorites – High KT Ir the same around the world – High abundances of osmium, gold and platinum – Shocked quartz: formed at high temperature and pressure – Spherical rock droplets: molten rock solidifies in air – Soot (some sites): widespread fires – 200 km crater in Yucatán peninsula: 10 km meteorite Mass Extinctions Methods – ~108 hydrogen bombs – Tidal wave up most of low-lying North America – Forest fires worldwide harsh winter plants die lack of food – Acid rain kill life in the oceans too – 99% of all living died, 75% of all species became extinct Colonization of Land • Microbes • – Hard to know when colonization occurred – Easy to find water and UV protection on land Larger organisms – Remained in the oceans longer, particularly animals – Need to draw water from the soil but energy from sunlight – Plant colonization of land began ~ 475 myr ago • Ozone – Main UV protection, but history even more uncertain than that of oxygen • Algae – DNA: plants evolved from algae – Algae plants in small pools during periods of dryness? • Carboniferous period – Animals followed plants to land within 75 myr – Large forests ~ 360 myr ago coal Other Mass Extinctions • Multiple mass extinctions – – – – – – At least 5 big ones Many smaller ones Event like KT every ~100 myr Old seafloor craters would be gone by now Nearby supernova explosions also every ~ 100 myr Magnetic reversals every few myr remove cosmic-ray protection of the magnetosphere • Evolution – Catastrophes create opportunities, not just disaster – May have more effect than gradual evolution Continuing Impact Threat • Impact objects – Meteor: small (<1 cm), ~ 25 million per day, burn in atmosphere – Fireball (not UFO): medium (10 cm 1 m), explode in the atmosphere – Meteorite: large (> few m), vaporizes solid rock, leaving a crater – Tunguska meteorite (1908): <30 m, energy of several atomic bombs, sound heard round the globe, no crater (comet?) • Future – Probability declines rapidly with size – Currently able to detect threat, but not divert it Colonization of Land • Microbes – Hard to know when colonization occurred – Easy to find water and UV protection on land • Larger organisms – Remained in the oceans longer, particularly animals – Need to draw water from the soil but energy from sunlight – Plant colonization of land began ~ 475 myr ago • Ozone – Main UV protection, but history even more uncertain than that of oxygen • Algae – DNA: plants evolved from algae – Algae plants in small pools during periods of dryness? • Carboniferous period – Animals followed plants to land within 75 myr – Large forests ~ 360 myr ago coal KT Event • Cretaceous-Tertiary (KT) transition: – Dinosaurs disappear “instantaneously” 65 myr ago • Meteorite event – – – – – – – Luis and Walter Alvarez: transition rich in iridium (Ir), like in meteorites High KT Ir the same around the world High abundances of osmium, gold and platinum Shocked quartz: formed at high temperature and pressure Spherical rock droplets: molten rock solidifies in air Soot (some sites): widespread fires 200 km crater in Yucatán peninsula: 10 km meteorite – – – – – ~108 hydrogen bombs Tidal wave up most of low-lying North America Forest fires worldwide harsh winter plants die lack of food Acid rain kill life in the oceans too 99% of all living died, 75% of all species became extinct • Mass extinction Other Mass Extinctions • Multiple mass extinctions – – – – – – At least 5 big ones Many smaller ones Event like KT every ~100 myr Old seafloor craters would be gone by now Nearby supernova explosions also every ~ 100 myr Magnetic reversals every few myr remove cosmic-ray protection of the magnetosphere • Evolution – Catastrophes create opportunities, not just disaster – May have more effect than gradual evolution Continuing Impact Threat • Impact objects – Meteor: small (<1 cm), ~ 25 million per day, burn in atmosphere – Fireball (not UFO): medium (10 cm 1 m), explode in the atmosphere – Meteorite: large (> few m), vaporizes solid rock, leaving a crater – Tunguska meteorite (1908): <30 m, energy of several atomic bombs, sound heard round the globe, no crater (comet?) • Future – Probability declines rapidly with size – Currently able to detect threat, but not divert it Moth Camouflage - Selection Genetic Drift: Bottleneck Founder Effect Bottleneck Founder Effect Phylogeny and Molecular Evolution • The history of the genes can provide us with information • about the structure and function, and significance of a gene or family of genes We can also use the reconstructed history to test hypotheses about evolution itself: – Rates of change – The degree of change – Implications of change, etc • We can then pose and test hypotheses about the evolution of phenomena unrelated to the genes – Evolution of flight in insects – Evolution of humans – Evolution of disease Assumptions made by phylogenetic methods: • • • • • • • The sequences are correct The sequence are homologous Each position is homologous The sampling of taxa or genes is sufficient to resolve the problem of interest Sequence variation is representative of the broader group of interest Sequence variation contains sufficient phylogenetic signal (as opposed to noise) to resolve the problem of interest Each position in the sequence evolved independently