Chapter 22- Descent With Modification: A Darwinian View of LifeDarwin 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 environmentsThese 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 creationo Genesiso Young Eartho Organisms unchanging Taxonomy- groupings of organisms1. 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 fossils2. 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.Geology3. Hutton- 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)4. Lyell- 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. Biology5. 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 Selection2. Fossils- Especially (weird) intermediate fossils- Reveals descent with modificationE.g. Archaeopteryx 150 myofossilsIntermediate to birds and reptilesIt 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 ANCESTORAnalogous 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 1location- Darwin’s explanation: Geographical isolation + Adaptation to explicit local resources = endemic species- E.g. finches on Galapagos IslandsChapter 23- The Evolution of PopulationsPopulation= SMALLEST unit of evolutionN. 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: Diploid1. Variants= alternative alleles at a locus2. Inherit 2 alleles/locus3. Dominant shows4. Law of segregation- random mating- re-associate (ensures mixing of alleles ina population).MODERN DEFINTION OF EVOLUTION= change in allele frequency in a population over timeN.S. changes allele frequencies Variation within the populationTypes of traitsPP ppSingle locus, no intermediate formsQuantitativePolygenetic traits (aka multiple genes for 1