Biology 1202 Test 1 Descent with Modification A Darwin View of Life The first convincing case of evolution was published by Charles Darwin in 1859 Evolution is the transformation of life forms on earth over time Descent with modification Evolution is change over time o A change in the frequency of the alleles of a population Mutation which favors one allele over another Mutation which creates a new allele that is favored o Change over a time period of generations For bacteria a day or two For humans maybe 200 300 years o Evidence of evolution Changes in phenotypes Look at the DNA genotype This is the fastest way Darwin s Ideas Were Opposed by Western Philosophy Creationism o All species were created exactly as they exist today o Most popular hypothesis o European Culture o Could be either strictly biblical or involve continual creation Fossils and a Record of Change Fossils are preserved remnants or impressions of an organism or something related to an organism that lived in the past o A succession of organisms is seen in the fossil record o The differences between fossils and living species are profound These results were not used to support evolution Catastrophism o A theory which states that the major changes in the earth s crust are the result of catastrophic events rather than gradual process of change o A French anatomist Georges Curvier founded the Science of Paleontology in the late 1700s The study of fossils o Curvier explained the layers of different species were caused by separate catastrophic events Geological Gradualism The predecessor of evolution In the late 1700 s a Hutton proposed that the large changes seen in the fossil records were the result of uniformitarianism o The principle that profound change is the cumulative product of slow continuous process o This was the first indication that the changes seen on earth were usually slow o If the changes were slow then the theological timeline of 6000 years must be in error Championed by Hutton and Curvier Pre Darwinian Theory of Evolution Lamarck placed fossils in an evolutionary context Lamarck compared modern species to the fossil record and identified several line of descent consisting of a succession of o Older fossils younger fossils modern species in 1809 Lamarck s comprehension model was published Lamarck envisioned many ladders of evolution which organisms could climb o The least complex organisms at the bottom of the ladders were spontaneously generated o The complexity of organisms increased in a march toward perfection and the most complex organisms were at the top of the ladder The mechanism of change involved two principles o Use and disuse Use it or lose it philosophy Acquired traits can be passed along to the next generation These ideas turned out to be wrong Darwin and the Voyage Charles Darwin 1809 1882 was born the year Lamarck published his work on evolution o Darwin was a nationalist He sailed on the voyage of the Beagle 1831 o Observed that South American organisms differed form European forms o Species of finches in Galapagos Islands were unique but resembled species of South America Darwin s work was preceded by the work of Wallace whose work in complete agreement with the hypotheses championed by Darwin o This work prompted a hesitant Darwin to complete the work he began years earlier Darwin s observations lead to The Origin of Species published in 1859 o Was a much more detailed book This is why we hear about Darwin and not Wallace Darwin used a tree as a metaphor for the history of life o At each branch or fork the species have a common ancestor Similar species have branched recently Species with greater differences branched long ago Most branches are dead ends Natural Selection Darwin s book focused on the role of natural selection in adaptation Darwin s observations and their inferences o Observation 1 Populations have potential for exponential o Observation 2 Population size is normally stable Inference 1 survival is a struggle only a fraction will o Observation 3 Traits are variable among individuals of a growth survive population Inference 2 Survival is not usually random but is largely dependent upon heritable traits Survival of the fittest o Observation 4 Most of those variable traits can be inherited Inference 3 Unequal survival of individuals will lead to gradual change in population Natural Selection is the differential success in the reproduction of different phenotypes resulting from the interaction of organisms with their environment Nature picks the phenotypes that will survive The result of natural selection is the adaptation of organisms to their environment o This adaptation is evolution Natural selection occurs from the interaction between the environment and the variability of the population o Variations arise by chance mutations o Environmental factors are defined by criteria Natural selection is insured by and excess of offspring and variation in the population Small changes accumulated each generation can result Biology 1202 Test 1 The Evolution of Populations Evolution and Population Evolution is the change in gene frequencies in the population Population is a localized group of individuals that belong to the same biological species o The smallest relevant evolutionary unit Individuals don t evolve Evolution measured by change in population Evolution acts only on heritable traits Populations Show Variations Some variation is the result of heritable changes mutation and or genetic recombination and some variations is non heritable Variation Between Populations Population of the same organism can show variations This population variation can often be geographic The variation between populations can be discrete or continual Frequently continual variation in a population will exist as a cline o Cline a graded variation in a trait that parallels a gradient in the environment The Integration of Darwinism evolution and Mendelism When the field of evolution and the study of populations merged with genetics the science of population genetics was formed o Population is the unit of evolution o Natural selection is the primary mechanism for evolutionary Population Genetics is the study of how populations change change genetically over time A Population Has a Genetic Structure Defined By Its Gene Pool The genes in a population make up the gene pool for that population any one time o Gene Pool is the total aggregate of genes in a population at All the alleles at all loci for all
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