Transcript Evolution
Adaptations Mesophyll cell Night CO2 4-C compound CO2 4-C compound CO2 CO2 CALVIN CYCLE CALVIN CYCLE Bundlesheath cell 3-C sugar 3-C sugar Day C4 plant CAM plant Evolution Ch 13 Charles Darwin 1874 1859 Voyage of the HMS Beagle On the Origin of Species… • Descent With Modification • By means of Natural Selection How Did Darwin Come Up With His Ideas? • Scientific Method • Key observations – Traits vary in a population – Most traits are inherited from parent to offspring – More offspring are produced than the environment can support (Thomas Malthus) Recap • Limited resources • Overproduction of offspring • Heritable individual variation – Therefore, survival depends partly on inherited features Darwin’s Theory of Evolution • In a varied population, individuals whose inherited characters best adapt them to the environment are more likely to survive and reproduce. • Therefore, more fit individuals tend to leave more offspring than less fit individuals. • Natural Selection is the mechanism – Reproduction (differential) is Key Darwin’s Theory of Evolution • Natural Selection is the mechanism – Reproduction (differential) is Key • Fitness- degree of adaptation to a specific environment • Adaptive if it enhances individual’s fitness Natural Selection Artificial Selection Observing natural selection • Camouflage adaptations that evolved in different environments A flower mantid in Malaysia A leaf mantid in Costa Rica Figure 13.5A Pestacide Resistance Chromosome with gene conferring resistance to pesticide Pesticide application Survivor Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow Figure 13.5B Support for Descent with Modification • • • • Biogeography Fossil Record Molecular Biology, Biochemistry, Cell Biology Comparative Anatomy Biogeography • Geographic distribution of species – Galápagos animals resembled species of the South American mainland more than animals on similar but distant islands – Organisms may have common ancestor Fossil Evidence – Organisms evolved in a historical sequence A Skull of Homo erectus D Dinosaur tracks B Petrified tree C Ammonite casts E Fossilized organic matter of a leaf G “Ice Man” F Insect in amber Figure 13.3A–G Fossil Evidence Many fossils link early extinct species with species living today Figure 13.3I Comparative Anatomy • Comparison of body structures in different species – Homology- similar characteristics resulting from common ancestry – Homologous structures- features with different functions but structurally similar due to common ancestry Figure 13.4A Human Cat Whale Bat Comparative Embryology •Comparison of early stages of development among different organisms Pharyngeal pouches Post-anal tail Human embryo Chick embryo Figure 13.4B Molecular Biology •Comparisons of DNA and amino acid sequences between different organisms to reveal evolutionary relationships Table 13.4 Unit of Evolution •Evolution acts on individuals, affects whole populations –Populations are the unit of evolution – Group of individuals of the same species living in the same place at the same time Unit of Evolution • Evolution is change in prevalence of heritable traits in population through time • A gene pool – Is the total collection of genes in a population at any one time • Microevolution – Is a change in the relative frequencies of alleles in a gene pool Hardy-Weinberg Equilibrium • Frequency of alleles in a stable population will not change over time – Very large population – Population is isolated – Mutations don’t alter gene pool – Random mating – All individuals are equal in reproductive success • In reality, this never happens Agents of Change • Genetic Drift – Bottle neck affect – Founder affect • • • • Gene Flow Mutation Non Random Mating Natural Selection Variation •Extensive in most populations •Mutation and sexual recombination generate variation and can create new alleles. Figure 13.11 Endangered species often have reduced variation • Low genetic variability • May reduce the capacity of endangered species to survive as humans continue to alter the environment Figure 13.10 Selection Models Sexual Selection • Sexual Dimorphism • Sexual Selection- where individuals with certain characteristics are more likely to obtain mates than others. – Intrasexual selection – Intersexual selection Selection • Heterozygote advantage – Balancing selection • Ex: Sickle cell anemia – Frequency-dependent selection • Fitness of genotype depends on frequency it occurs • Ex: mimicry – Neutral Variation • Little to no impact on phenotype or fitness • Natural Selection cannot distinguish alleles Natural Selection is Limited • • • • Only act on existing variation Historical constraints Compromise Chance, selection and the environment