Biology Chapter 23: Systematics and Evolution

Chapter 23: Systematic, Phylogenies, and Comparative Biology

• Systematics

  • All organisms share many characteristics (cells, DNA, physical traits, metabolism, ATP)
  • Difficult to determine close relationships

• Branching Diagrams

  • Show relatedness among things
  • Various ways to represent relationships
  • Indicate who is more closely related to whom

• Similarity and Evolution

  • Similarity does not always predict evolutionary relationships
  • Evolutionary rates can vary, some genes may evolve faster than others
  • Evolution may not be unidirectional: e.g., manatees evolved from land to water, then back to water
  • Convergent evolution is possible
  • Question: How much time has passed since divergence influences similarity of species.

• Cladistics

  • Analyze ancestral traits and derived traits
  • Ancestral characteristics are inherited from the most recent common ancestor of a group
  • May not distinguish between individuals in the same group

Cladistics Methods

• Ancestral vs. Derived Characters

  • Presence of hair is a shared derived feature in mammals
  • Traits being ancestral or derived can change depending on context
  • Lung presence in mammals is an ancestral trait

• Characters can be morphological, physiological, behavioral, and ecological

• Other Cladistics Method Concepts

  • Character states for example presence or absence of tail in vertebrates
  • Using outgroups to create comparisons of groups
  • Synapomorphy: A new derived trait of a group
  • Symplesiomorphy: A shared ancestral trait in a group and an outgroup

Chapter 20: Evolutionary Change

• Processes that lead to evolutionary change
  • Natural selection affects allele frequencies

Population Genetics

• Study of genes in populations
  • Understanding genetic variations within populations
  • Natural populations contain considerable genetic variation

Hardy-Weinberg Principle

• This principle explains when populations do not evolve

• Proportions of genotypes remain constant under certain conditions (no mutation, no gene flow, and no selection)

• If these conditions aren't met, change in allele frequencies occurs showing a population is evolving

• Agents of Evolutionary Change

  • Mutation: Fundamental unit of change
  • Natural Selection

• Factors influencing evolution

  • Gene flow
  • Non-random mating
  • Genetic drift
  • Random allele frequency change

Evidence for Evolution

• Beaks of Darwin's Finches

  • Darwin collected finches from Galapagos Islands
  • Studied beak diversity in relation to what they eat
  • Beak shape as a result of food selection

• Artificial Selection

  • Changing species characteristics through breeding
  • Examples in dogs, crops (e.g., brassicas), etc.

Chapter 21: Fossil Evidence

• Fossil Evidence

  • Organisms buried in sediment form fossils

• Fossil age estimation

  • Relative position to determine age (deeper = older)
  • Isotopic dating to calculate precise age
  • Potassium and Carbon dating methods

• Evolutionary Transitions

  • Evidence of transitions from one form to another
  • Examples: lizards to birds, apes to humans
  • Intermediate forms have been found

• Anatomical Evidence

  • Examining anatomical structures (similar structures = shared ancestor)
  • Examples: comparing forelimbs in diverse organisms

• Embryology

  • Studying early stages of development
  • Embryonic similarities in diverse organisms

• Vestigial Structures

  • Structures with reduced function, but still present
  • Examples: human appendix, whale pelvis

Biogeography

• Studying distribution of organisms and their relationships to their environment and evolution
• Distribution patterns can reflect common ancestry

Chapter 23: Additional

• Evolution by Natural Selection

  • Natural selection: The differential survival and reproduction of organisms based on traits.
  • Necessary conditions: variation, variation causes differences in offspring, genetic influence of variation

• Fitness

  • Measure of an organism's ability to survive and reproduce
  • "Fittest" organisms have the greatest reproductive success

• Sexual Selection

  • Selection based on an organism's ability to attract mates
  • Traits favored for mating may be detrimental for general survival

• Selection types

  • Stabilizing selection (favors average traits)
  • Directional selection (favors one extreme)
  • Disruptive selection (favors both extremes)

Chapter 23: Additional topics and selection

• Types of Selection

  • Stabilizing, directional, and disruptive selection
    • Selection types and how environmental pressures change the selection

• Maintenance of Variation

  • Frequency-dependent selection: The fitness of a phenotype depends upon its frequency within the population
    • Rare phenotypes can be favored, uncommon traits are favored
  • Positive frequency-dependent selection: favors common traits, tends to reduce variations
  • Negative frequency-dependent selection: rare traits are favored by selection, increases variability