Chapter 22 Descent With Modification A Darwinian View of Life Darwin Observed 3 Things 1 Adaptations organisms well adapted to their environment organisms can change 2 Many shared characteristics Are they related 3 Rich Diversity consequence of adaptation to specific environments These observations were explained by the concept of Descent With Modification aka Evolution Adaptations that are beneficial to the current environment are passed on to progeny but only heritable adaptations i e genetically encoded Previous Theories Before Darwin Early World View Aristotle Greek philosopher who suggested that life might have changed gradually over time o Viewed species as fixed unchanging o Conclude that life forms could be arranged on a ladder or scale from smallest to most complex Scala Naturae Old Testament account of creation o Genesis o Young Earth o Organisms unchanging Taxonomy groupings of organisms 1 Linnaeus Father of Taxonomy Groupings based on shared characteristics then used morphology LRG Domain Kingdom Phylum Class Order Family Genus Species SML He did not interpret these shared characteristics as evidence of evolution Darwin however saw shared characteristics as originating from a common ancestor Paleontology study of fossils 2 Cuvier Father of Paleontology Fig 22 3 Fossils indicate extinction occurs Catastrophism a local catastrophe led to the extinction of local species causing fossils Different species would repopulate the area then the process would continue He did not contribute this to evolution He thought the species was unchanging but had moved to a new area Geology 3 Hutton 4 Lyell Gradualism small movement but over time can totally change the landscape Darwin thought Gradualism was an analogy for biological change I e evolution descent with modification Uniformitarianism the rate of geological change is constant and very slow Darwin thought uniformitarianism made enough time for evolution of extant existing species to have occurred Both concepts led to the conclusion that the Earth is very old Biology 5 Lamarck Believed Evolution occurs Characteristics that benefit are passed on Species adaptation evolution Problem acquired or environmentally induced traits CANNOT be inherited Fig 22 4 ex steroids child will not inherit physical strength Darwin realized that only genetically encoded heritable characteristics were passed on 6 Maltus Observed that species over produce More individuals than resources can support All of this led to DARWIN S THEORY Competition between individuals Survival of individual best adapted to current condition Survival of the Fittest Charles Darwin Darwin s Beagle Voyage 1831 1836 Galapagos Islands isolated volcanic islands supposed to travel 2 years but travelled 5 years Animals were not quite the same as those on the mainland but did resemble them Darwin s Finches Beaks specialized due to island adaptation fig 22 6 food Adaptation due to process of Natural Selection Finch species share characteristics common ancestor Decent with Modification South America Temperate plant species resemble local plants NOT temperate plants in climate Temperate climate plants evolved from a local plant species DARWIN S MECHANISM OF EVOLUION Natural Selection analogous to the practice of artificial selection the mechanism driving adaptation fig 22 9 Natural forces do the selection E g climate conditions predation intra species competition Implicit in this is o There is variation with a population o Individuals vary in their adaptations o Some variation is genetically encoded Natural Selection only acts on this o Some variation is acquired Survival of the Fittest o Fitness ability of an individual to survive and reproduce and pass its genes on to its progeny N S is not due to chance Darwin s Theory of Evolution explains observations such as 1 Natural Selection 2 Fossils Especially weird intermediate fossils Reveals descent with modification E g Archaeopteryx 150 myofossils Intermediate to birds and reptiles It has characteristics of both Darwin s Descent w Modification explains how reptiles evolved to birds and that this fossil is in an intermediate state 3 Homology Organism of species share characteristics b c of a common ancestor same structure but different function Many points of similarities Not always the same function Adaptations in common ancestor homologous traits Fig 22 7 Anatomical vs Molecular Anatomical shares physical traits Ex limbs humans bats whales etc very similar Molecular Share genes proteins Ex electron transport is fundamental to all cells genes encoding ETC proteins in bacteria and humans are very similar 4 Convergent Evolution Analogy Fig 22 17 Same adaptation to similar challenge same function but different structure Few other common characteristics Adaptation NOT IN A COMMON ANCESTOR Analogous Vs Homologous Count points of similarity Do the organisms have other points of similarities YES many homologous NO few analogous convergent Evol 5 Biogeography Fig 25 14 Distribution of species especially endemic species species found in 1 location Darwin s explanation Geographical isolation Adaptation to explicit local resources endemic species E g finches on Galapagos Islands Chapter 23 The Evolution of Populations Population SMALLEST unit of evolution N S acts on individuals in population affecting their survival The population composition changes and evolution occurs Evolution Only genetically encoded heritable characteristics count Phenotype o Environmentally induced o Genetically encoded this one counts Genotype alleles at a locus phenotype expression application of a trait Mendel s Law of Inheritance Diploid 1 Variants alternative alleles at a locus 2 Inherit 2 alleles locus 3 Dominant shows 4 Law of segregation random mating re associate ensures mixing of alleles in a population MODERN DEFINTION OF EVOLUTION change in allele frequency in a population over time N S changes allele frequencies Variation within the population Types of traits PP pp Single locus no intermediate forms Quantitative Polygenetic traits aka multiple genes for 1 trait vary over a continuous range Sources of Genetic Variation 1 Recombination random mating random association of gametes Fresh combination of alleles new phenotypes MAJOR source of variation for DIPOID ORGANISMS 2 Mutation minor source for diploids DNA genome mutation rate is VERY LOW Point Mutations Not all mutations are bad detrimental Missense alter codon change in Amino Acid Non sense altered codon