Transcript EVOLUTION
EVOLUTION A SCIENTIFIC THEORY I. The History Carl Linneaus (18th century)– The father of taxonomy. Used binomial nomenclature, came up with the hierarchical classification theme, used visible characteristics to classify plants and animals. Thomas Malthus (18th – 19th century): Attempting to justify the conditions of the poor by stating that poverty and starvation were merely a consequence of overpopulation. http://www.pbs.org/wgbh/evolution/library/02/5/l_025_01.html Lamarck (18th – 19th century) – First to publish a reasoned theory of evolution: A) the idea of use and disuse B) inheritance of acquired characteristics Lyell (19th century) – natural processes form geological formations over a long period of time, erosion and other forces that shape rocks are very slow processes that take millions of years, so the earth must be older than previously believed. Wallace (19th – 20th century): theory of evolution by natural selection. Charles Darwin (19th century) – theory of evolution by natural selection. II. What is a scientific theory? A widely accepted explanatory idea that is broad in scope and supported by a large body of evidence. http://www.pbs.org/wgbh/evolution/library/11/2/e_s_1.html III. Natural Selection Natural Selection: The process in nature by which, only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated. As a result the POPULATION EVOLVES – or changes over time. The five aspects (steps) of natural selection: Variation – individuals exhibit variation in a population, they have a unique set of traits. Some of these traits improve their chances of survival while others are less favorable. Overproduction – populations produce too many young, many must die. Struggle for existence – food, water and other resources are limited, organisms are compete with one another for these resources. Differential reproductive success – those individuals that have the most favorable characteristics in an environment, has higher chance of reproduction. Descent with modification – the varying reproductive success result in a change in the population – the more successful traits become more common http://www.pbs.org/wgbh/evolution/library/01/6/quicktime/l_016_08.html http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html IV. Evidence of Evolution The fossil record – remains or traces of previously lived organisms (shells, amber, prints, skeletal remains). Mostly found in sedimentary rocks Their age can be determined by radiometric dating http://www.pbs.org/wgbh/evolution/library/03/3/l_033_01.html Comparative anatomy: homologous structures – structures that have similar origins but may look different from the outside. Analogous structures -- may look similar but have different origins Vestigial structures – structures that are not used any more but were used by our ancestors Biogeography of animals and plants and continental drifts (geographic distribution of species) – organisms with similar origin tend to live in the same area http://www.ucmp.berkeley.edu/geology/anim1.html -- so similar fossils from different continents could be found Developmental biology – the embryos of related species look similar during their early embryonal development. Artificial selection – humans select traits of organisms for human benefits (domestication) Molecular comparisons: Universal genetic code Proteins and DNA (the closer related two species are the more similar their DNA and proteins are) Molecular clocks Biogeography – geographic distribution of species. V. The Mechanisms of Evolution Natural selection – you already know this one. Mutations (small changes in the nucleotide sequence of DNA) result in new traits and increasing variation in the population. One mutation alone usually does not change the population, however, beneficial mutations can cause some change Genetic drift – change in the allele frequency in a population based on chance Founder effect – small group of organisms move away from the main population and give rise to a new population Bottleneck effect – after a natural disaster, a small group of organisms with different characteristics survive Gene flow – movement of organisms from one population to another Nonrandom mating – sexual selection, selecting mates because of their visual traits. http://www.youtube.com/watch?v=cEh-zclVo44 VI. Examples of Evolution Industrial Melanism Human birth weight Heterozygous advantage Darwin’s finches Antibiotic and pesticide resistance VII. Modern Evolutionary Theory Several scientists improved on Darwin’s theory and this improvement is still going on. We know that POPULATIONS EVOLVE NOT INDIVIDUALS Today we explain the causes of evolution with mutations, changes in DNA and sexual reproduction. Evolution is closely related to genetics. http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html Today’s definition of evolution: Genetic change in a population or species over generations; all the changes that transform life on Earth; these heritable changes produced Earth’s diversity of organisms Just for fun: http://www.youtube.com/watch?v=T1_vnsdgxII