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Central Question to Early Scientists: what explains the vast diversity and surprising similarity of life? Unity – All organisms share some traits. Diversity – Organisms are dramatically different. Unity RNA Protein Diversity • >1.5 million named species • Life in all corners of the word • Most species seem to ‘fit’ in with their environment • Some species have adaptations for seemingly different habitats • Why are there so many different species? A small sample of biological diversity How can we explain the diversity of life on this planet? History of evolution • History of science is important to understand the philosophy of science • How did scientists and society explain adaptations and how did this understanding shape their view of the world Fit of structure to function Fit of structure to function Similar features of different species Adapted to their environment Adapted to their environment Changing view of science through history • philosophy of science swung between rationalism and empiricism • Rationalism – ideas first, data later. Similar to mathematics based on ideal principles. Used by the Greeks • Empiricism – gather data then develop ideas. Developed by the British late 1700’s The Greeks • Were first to formalize scientific understanding • Others were doing science at the time but the Greeks codified these ideas Greek explanation of variation • Socrates/Plato: variance doesn't matter, only essences of forms • Different tables are simply variants of an ideal table. Aristotle/Plato – Ideal member of the species – Some where there is a perfect tiger or human or bird – All other organisms strive to approach this perfection – Variation of species are mistakes of this perfection – Do we think this way? Scala Naturae: great chain of being • Need to rank objects, organisms and objects on a scale of perfection • Humans (land owning Greek men) at the top rung, dirt and moss on the bottom rung • Does our culture have similar ideals? Middle ages in Europe • No human could approach the genius of the Greeks • Scholars copied texts • New ideas were not looked on favorably Middle ages in Arab countries • Mathematics and sciences continued • More empirical than Greek or Roman science • Scientific method similar to modern method • European countries were able to import these ideas Renaissance • Printing press – Allowed information to be quickly transmitted • Global travel – Brought new plants and animals to European attention – Maps expanded world view Accepted views in Europe • Scala Naturae: great chain of being ("ladder of life") • Inanimate objects • Plants • Lower animals • Man • Angels • God A new view of biologic variation • A Natural perspective viewed biologic variation not as a corruption of the ideal form but as characteristics. • A species could have some or all of these characteristics And scientists were finding ‘new’ species Figure 22-03 Catastrophism • Georges Cuvier an early 19th century French anatomist • Attempted to explain the patterns of extinction and succession observed in the fossil record • Thought Earth was young and species unchanging • Miracles are an agent of change 1800’s • Gradualism – Slow series of natural process – Laws of nature were not disrupted (no miracles) – Disturbances such as earthquakes and volcanoes were the result of natural not supernatural processes • Uniformitarianism – You can understand the past by looking at what is happening today. – The past is a multiplication of current processes Snake River Canyon Grand Canyon • James Hutton (‘father of geology’) gradualism (1788) and Charles Lyell: uniformitarianism: called • wrote the principles of geology that Darwin took with him on his travels. Jean Baptiste de Lamarck • Failed novelist • Botanist • Father of Paleontology (study of fossils) • Proposed that species changed through time (gradualism) Theory of Acquired Characteristics • Lamarck suggested a mechanism, inheritance of acquired characteristics. • Children inherit traits that their parents acquire through life. • So a giraffe got its long neck by stretching it and passing that longer on to its offspring. • Organisms strove to ascend the ladder of life plants strove to become animals, ect Two problems with Lamarck’s theory • It’s goal-oriented: suggests that evolution occurs to satisfy a need that a species has. • Inheritance of acquired characteristics. – How could we test this? Mid 1800’s Rationalism to Empiricism • Understanding that the Earth was many million of years old • Similarity of fossils and living organism • Many agreed with common decent • Evolution (change over time) was generally accepted • English and American scientists wanted a mechanism to explain diversity Charles Darwin • As a young man dropped out of medical school. • Entered the seminary • Convinced his father to let him travel for 5 years around the world Darwin’s Voyage on the Beagle Evidence Darwin found Geographic variation of species • Galapagos Islands: The resemblance of the different finches (a variety of bird) on the individual islands caused him to question the “fixed” nature of species. • On Continents: Observed differences between “fixed” species when they were separated by long distances on the mainland Adaptive radiation • Occurs whenever there are open niches. • Some individuals of a species expand into unfilled niches (roles) in the environment. • Thus, over LONG time periods through selective reproduction and genetic variation, the population may evolve slightly and better fit that role. Darwin talked to pigeon and plant breeders about artificial selection • By selective breeding, you can change appearance of birds, dogs, cattle Terminal bud Lateral buds Brussels sprouts Cabbage Leaves Flower clusters Kale Cauliflower Stem Flowers and stems Broccoli Wild mustard Kohlrabi Thomas Malthus • An Economist • Essay On the Growth of Populations gave Darwin the idea that not all young can survive. • Malthus worried that the Earth would soon overpopulate. Received letter from Alfred Russel Wallace • Darwin spent 20yrs working on Origin of Species • Darwin received Wallace’s paper about a theory of evolution by natural selection. • Wallace asked Darwin to publish his paper if he liked it Darwin’s Principles First Principle • For any species, population sizes would increase exponentially if all individuals that were born reproduced successfully. A mushroom produces millions of spores A mustard plant produces ¾ million seeds/yr A sea hare produces over a million eggs/yr Elephants • Gestation period of 22 months and produce one calf. – Say we start with 500 elephants. – And each female produces 1 calf every 22 months. – In only 50 generations there would be how many elephants (Hint, calculated the same as compound interest) 143,813,294 elephants But populations remain relatively stable WHY? Limited Resources • • • • • Food Water Nutrients Habitat Mating partners Second Principle • Survival of the fittest – The reproductive potential of populations exceeds the capacity of the environment to support them. Reproductive over capacity makes a struggle for existence among individuals inevitable. Reproductive Overcapacity Third Principle • Individuals of a population vary in their characteristics. Much of this variability is heritable. Population = a group of potentially interbreeding organisms that share the same gene pool and are geographically linked Millions of offspring=millions of variations that can be selected Fourth Principle • Individuals with heritable traits “best suited” to the local environment leave a disproportionately large number of offspring. Fourth Principle • Disproportional representation by individuals with the “best suited” traits increases the overall frequency of these traits in the next generation. Disproportionate Representation Fifth Principle • The effects of differential reproductive success accumulate over generations to bring about evolutionary changes in populations. LE 1-20 Population of organisms Overproduction and competition Hereditary variations Differences in reproductive success Evolution of adaptations in the population Summary of principles of evolution by natural selection 1. Genetic variation within a population 2. Reproduction exceeds carrying capacity (limited resources) 3. Competition for resources: Survival of the fittest 4. Survivors increase proportion of genes within population • Leads to evolutionary change of population over time Evolution is a Population Phenomenon Individuals do not evolve; populations do. • Individuals are either favored or disfavored by selection but individuals do not evolve in a heritable way. • However, selection can lead to changes in populations. Fitness • Fitness is the degree of success measured as the relative contribution to the next generation. • Fitness can be determined from the rate of survival through a selective phenomenon. Important to Remember • Evolutionary Success does not always go to the biggest or strongest but to the individuals who produce the most viable offspring. • Why do farmers need to re-apply pesticides to their fields? If a population lacks necessary variation they may go extinct Natural Selection Review Natural Selection • The environment acts as a filter favoring some variations over others. • Environmental factors vary from place to place and from time to time. • Therefore, the specifics of natural selection are regional and timely. Natural Selection • Differential reproductive success is made possible by variation and overproduction. Natural Selection • Selection does not create variations • Natural selection works as an ‘editor’ to existing variation Natural Selection • Selection is an editing process that increases the relative frequency of certain variations that arise randomly. • Natural selection is the mechanism that explains evolution. There are other factors to evolution such as mutation and genetic drift Natural Selection • Natural selection is not intentional. – Individuals do not decide to change. • Individuals do not change • individuals do no decide to mutate in order to adapt to changing environmental pressures. LE 1-21a Population with varied inherited traits LE 1-21b Elimination of individuals with certain traits LE 1-21c Reproduction of survivors LE 1-21d Increasing frequency of traits that enhance survival and reproductive success