BIOL TERMS

Page 1: Introduction to Evolution Before Darwin

Historical Views

  • 4th Century BC Philosophers

    • Plato: Believed life was unchanging; observations were limited to current events.

    • Aristotle: Asserted organisms do not change; proposed the Scale of Nature (Scala Naturae).

      • Ranked organisms from simple (inorganic) to complex (humans and angels).

      • Influenced by the Old Testament—humans viewed as perfected creations by God.

Revolutionary Ideas

  • Linnaeus: Developed a classification system categorizing organisms by genus and family.

  • Hutton: Introduced the theory of gradualism—change occurs gradually over time.

  • Lamarck: Proposed a theory of evolution through use and disuse of traits.

  • Lyell: Published Principles of Geology, suggesting fossils as evidence of past life.

  • Darwin: Known for his voyage on the HMS Beagle and for publishing Origin of Species.

  • Wallace: Sent observations on natural selection to Darwin, prompting further discussion.

  • Mendel: Established principles of inheritance through experiments with pea plants.

Key Concepts in Paleontology

  • Paleontology: Study of fossils, important for understanding life history.

  • Fossils: Remains of hard parts of organisms found in rock strata.

  • Sediment: Carried by erosion; older fossils found in deeper layers of rock.

  • Mineralization: Process where remains disappear and new forms appear.

  • Catastrophism: Hypothesis suggesting natural disasters cause extinction of species.

Lamarck's Theories

  • Use and Disuse: Characteristics gained or lost through use or lack thereof could be inherited.

Page 2: Key Observations from Darwin

  • Darwin’s Voyage: On HMS Beagle, Darwin noted adaptations in finches based on bill size related to habitat and diet.

Key Concepts in Evolution

  • Descent with Modification: Refers to gradual change in traits over generations influenced by environmental pressures.

  • Tree of Life: Concept of life’s history viewed as a branching tree, not a ladder (as proposed by previous thinkers).

Key Observations Made by Darwin

  • Variation in Populations: Examples include observable differences in morphology, such as in ladybug coloration.

  • Overproduction of Offspring: Species tend to produce more offspring than can survive, leading to competition.

  • Natural Selection: Process where individuals with advantageous traits are more likely to survive and reproduce.

Page 3: Evidence for Evolution

Darwin’s Explanation vs. Lamarck

  • Neck Lengths in Giraffes: Darwin explained variations in neck lengths through genetic differences, while Lamarck attributed changes to use and disuse.

  • Artificial Selection: Example of how domesticated plants or animals diverge from their wild ancestors such as wolves to dogs and wild mustard to various vegetables.

Evolutionary Tree

  • Branch Point: Represents a common ancestor in evolutionary trees.

Evidence of Evolution

  1. Resistance:

    • Pest Resistance: Pests adapt to pesticides, leading to populations resistant to chemicals.

    • Drug Resistance: Example: MRSA survives due to inadequate antibiotic dosing.

    • Studying Beak Size: Soapberry bugs exhibit varying beak lengths depending on fruit types.

  2. Homology:

    • Shared anatomical structures due to common ancestry, e.g., forelimbs of bats and whales.

Page 4: Homologous Structures

  • Embryonic Development: Observing similar structures during development reveals evolutionary relationships (e.g., pharyngeal pouches, post-anal tail).

  • Molecular Homologies: Similarities in DNA and protein sequences; closer relatedness inferred from higher percentage of amino acid similarity.

Convergent Evolution

  • Distinct evolutionary lineages develop similar traits due to similar environmental pressures (e.g., flying creatures like sugar gliders vs. flying squirrels).

Page 5: Phylogeny and Classification

Definition of Phylogeny

  • Phylogeny: Evolutionary history and classification system based on shared common ancestors.

  • Systematics: Classifying organisms and determining their evolutionary relationships utilizing fossil and DNA evidence.

Binomial Nomenclature

  • Developed by Linnaeus, includes a two-part naming system for species using genus and species names.

  • Taxonomic Hierarchy: Levels include kingdom, phylum, class, order, family, genus, and species.

Understanding Phylogenetic Trees

  • Branch Point: Indicates divergence of lineages.

  • Polytomy: Unresolved pattern in divergence indicating multiple lineages.

Conservation Biology

  • Use of mitochondrial DNA comparison to assess legality of species harvesting.

Homology vs. Analogy

  • Homology: Shared characteristics due to common ancestry.

  • Analogy: Similar traits arise from adaptations to similar environments (e.g., different species exhibiting similar flying traits).

Page 6: Molecular Homology

  • DNA Sequencing: Comparisons of DNA sequences involve aligning sequences to determine degree of homology.

  • Challenges: Errors from DNA replication, such as deletions or insertions complicate comparisons.

  • Measurement Standard: At least a 25% similarity required for homology.

Page 7: Phylogeny Continued

  • Shared Characteristics: Utilized to construct phylogenetic trees and classify groups (taxa).

Types of Groups



a. Monophyletic Group (Clade): Grouping that includes one common ancestor and all its descendants.b. Paraphyletic Group: Group that doesn’t include all descendants of a common ancestor.c. Polyphyletic Group: Group that includes organisms with multiple evolutionary ancestors due to convergent evolution.

Branch Length

  • Significance: Indicates genetic change and relative time of divergence in evolution.

Page 8: Maximum Parsimony and Molecular Clocks

  • Maximum Parsimony: Simplest explanations aligned with facts are more likely accurate (Occam's razor principle).

  • Example: Closest living relatives of birds are crocodilians based on shared traits like a 4-chambered heart.

Molecular Clocks

  • Concept: Measures evolutionary change over time based on consistent gene/region mutations.

  • Limitations: Back estimation becomes unreliable; useful for events not evident in fossil records.

    • Key Points:

      1. Patterns of descent versus phenotypic similarities.

      2. Branching sequences don't indicate absolute ages.

      3. Closest taxa evolved from common ancestors, not directly from one another.

Page 9: Interpreting Evolution

Life Domains

  • Three Kingdoms of Life: Eukarya, Bacteria, Archaea.

Horizontal Gene Transfer

  • Movement of genes between organisms outside traditional reproduction methods, e.g. via plasmids or viral infection.

  • Endosymbiosis: Theory explaining the origin of mitochondria and chloroplasts in eukaryotic cells.

Population Genetics

  • Genetic Variation: Controlled by alleles; studied through discrete and quantitative characters.

    • Heterozygosity: Average percentage of loci that are heterozygous within a population.

Sources of Genetic Variation

  1. Mutation: Errors in DNA replication during meiosis can create new alleles.

  2. Sexual Reproduction: Provides genetic recombination leading to variation.

Page 10: Hardy-Weinberg Principle

  • Hardy-Weinberg Equation: Used to test if a population is evolving.

  • Key Terms:

    • Gene Pool: Total alleles in a population.

    • Allelic Frequency: Proportion of a particular allele in the gene pool.

    • Genotypic Frequency: Proportion of individuals of specific genotypes.

    • Hardy-Weinberg formula: p² + 2pq + q² = 1.

      • Calculation example: AA = 17, Aa = 2, aa = 1.

Conditions for Hardy-Weinberg Equilibrium

  1. No mutations.

  2. Random mating occurs.

  3. No selection pressures.

  4. Very large population size.

  5. No gene flow between populations.

Page 11: Evolution Mechanisms

Genetic Drift

  • Random events causing allele frequency changes; affects small populations more critically.

    • Founder Effect: Small group breaks off and forms a new population.

    • Bottleneck Effect: Large population significantly reduced by an event, altering allele frequencies.

Effects of Genetic Drift

  • Can lead to reduced genetic variation and fixation of harmful alleles, diminishing population viability.

  • Natural Selection: More effective with greater genetic variability.

Gene Flow

  • Exchange of alleles reduces differences between populations.

Modes of Selection

  1. Directional Selection: Favors one extreme phenotype.

  2. Disruptive Selection: Favors both extreme phenotypes.

  3. Stabilizing Selection: Favors average phenotypes.

Balancing Selection

  • Maintains genetic diversity; can involve advantageous heterozygote traits, e.g., sickle cell anemia's protective advantage against malaria.

Page 12: Sexual Selection

Concepts

  • Sexual Dimorphism: Two distinct forms (males and females).

    • Examples: Lions, deer, and birds.

  • Polymorphism: Many forms exist within a species.

Types of Sexual Selection

  • Intrasexual Selection: Competition among males for female attention.

  • Intersexual Selection: Females selecting mates based on specific traits or behaviors.

Neutral Variation

  • Traits with no significant effect on reproductive success.

Natural Selection's Limitations

  • Cannot generate perfect organisms; only works with available variations and existing structures.

Page 13: Origin of Species and Speciation

Speciation Defined

  • Process of one species diverging into two or more species.

Biological Species Concept

  • Defines species based on reproductive isolation; interbreeding groups must be naturally isolated from other groups.

Reproductive Isolation Mechanisms

  1. Prezygotic Barriers: Prevent mating or fertilization.

  • Examples: habitat, temporal, and behavioral isolation.

  1. Postzygotic Barriers: Affect hybrid viability and fertility after fertilization.

  • Examples: reduced hybrid viability, infertility, hybrid breakdown.

Other Species Definitions

  1. Morphological Species: Defined by physical traits.

  2. Ecological Species: Defined by ecological niches.

  3. Phylogenetic Species: Based on evolutionary relationships to a common ancestor.