Evolution Ch 13

Historical Theories Anaximander (~2500 yrs ago) Aristotle Georges Buffon (1700’s) Jean Baptist Lemark (late 1700’s - early1800’s) Erasmus Darwin

Charles Darwin

Voyage of the HMS Beagle

On the Origin of Species… Descent With Modification By means of Natural Selection

Support for Descent with Modification Biogeography Fossil Record Molecular Biology, Biochemistry, Cell Biology Comparative Anatomy

Biogeography Geographic distribution of species – Darwin noted that 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 C Ammonite casts B Petrified tree E Fossilized organic matter of a leaf G “Ice Man” Figure 13.3A–G F Insect in amber

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 Human CatWhale Bat Figure 13.4A

Comparative Embryology Comparison of early stages of development among different organisms Post-anal tail Pharyngeal pouches Chick embryo Human embryo Figure 13.4B

Molecular Biology Comparisons of DNA and amino acid sequences between different organisms to reveal evolutionary relationships Table 13.4

How Did Darwin Come Up With His Ideas? Scientific Method Key observations – Traits vary in a population & most are inherited from parent to offspring – More offspring are produced than the environment can support (Thomas Malthus)

Trait Variation

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, they tend to leave more offspring than less fit individuals. Natural Selection is the mechanism – Reproduction (differential) is Key

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 Pesticide application Survivor Chromosome with gene conferring resistance to pesticide Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow Figure 13.5B

Antibiotic resistance The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria Colorized SEM 5,600  Figure 13.13

Natural Selection Experiment Darwin Finches (Galapagos Finches) Similar EXCEPT for beaks – Beaks = specialization

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 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

Types of Selection

Sexual Selection Sexual Dimorphism Sexual Selection- where individuals with certain characteristics are more likely to obtain mates than others. – Intrasexual selection – Intersexual selection

Diploidy Heterozygote advantage Balancing selection Frequency-dependent selection

Natural Selection is Limited Only act on existing variation Historical constraints Compromise Change, selection and the environment