JM

Darwin And Evolution L4

Darwin And Evolution Lecture 3 Notes

Heritable Change in Evolution

  • Definition: Heritable change refers to changes in a population of organisms that are passed down from one generation to the next.
  • Population: A group of individuals of the same species inhabiting the same area, with potential for interbreeding.

Charles Darwin (1809-1882)

  • Description:
    • English naturalist, geologist, and biologist.
    • Proposed that all species of life descended from a common ancestor.
    • Developed the theory of natural selection, which later became recognized as the basic mechanism of evolution during the modern synthesis (~1950s).

Theory of Natural Selection

  • Definition: The process which eliminates individuals that are less likely to survive and reproduce in a particular environment, while allowing other individuals with traits that confer greater reproductive success to increase in numbers.

Charles Darwin's Studies

  • Studies conducted on:
    • Beetles
    • Fish
    • Marine invertebrates
    • Pigeon breeders
    • Fossils
    • Barnacles
  • Key aspects of Darwin’s theory:
    • Descent with modification through variation & natural selection.

Descent with Modification

  • Concept: Existing species result from modifications of pre-existing ones through common ancestors.

Variation in Traits

  • Heritable traits: Traits that are passed from parents to offspring; foundational to the study of genetics.
  • Natural Selection:
    • In each generation, organisms with traits better suited for their immediate environment produce more offspring.
    • As a result of natural selection, traits favoring reproductive success become more common in a population over time.

Genetic Change and Evolution

  • Evolutionary change involves changes in genetic material (molecular level):
    • DNA (Deoxyribonucleic Acid): The blueprint for the organization, development, and function of all living things.
    • Passed from parents to offspring.
    • Generally stable across generations.
  • Genes: Segments of DNA.
    • Govern characteristics or traits of organisms by encoding proteins.
    • Changes in genetic material can lead to the formation of new proteins.
    • Mutations: Heritable changes in genetic material.

Mutations and Their Impact

  • Definition of mutations: Heritable changes in genetic materials that can produce observable effects (phenotypes).
    • Phenotype: Observable characteristics of an individual resulting from the interaction of its genotype with the environment.
  • Types of effects from mutations:
    • Neutral: No observable effect.
    • Beneficial: Enhancements in survival and reproduction.
    • Detrimental: Impairment in survival and reproduction.
  • Environmental factors play a role in determining whether mutations are seen as beneficial, neutral, or detrimental.
  • Without reproduction, mutations cannot be passed through a lineage.

Evolutionary Change in Genetic Material: Vertical Descent with Mutation

  • Concept: Genetic material is passed down across generations, with mutative changes accumulating over time. Effects may be neutral, detrimental, or beneficial concerning the organism's current environment.

Vertical Descent with Modification

  • New species arise from pre-existing species over time.
    • Fossil Records: Provide evidence for evolutionary change (e.g., the evolution of whales from terrestrial mammals).
    • Examples of transitions:
    • Pakicetus: Ancestral form spending time in fresh water.
    • Ambulocetus: Intermediate form with swimming adaptations.
    • Rhodocetus: Adaptations for a fully aquatic lifestyle, with physical changes such as reduced hind limbs and a tail fluke.
    • Modern Whales: Exhibit traits such as blow holes and lost hind limbs.

Atavistic Traits

  • Definition: Modifications of biological structures where ancestral genetic traits reappear after being lost through evolutionary changes in previous generations.

Evolutionary Change in Genetic Material: Horizontal Gene Transfer

  • Process: Gene transfer between organisms (especially bacteria).
    • Unlike vertical evolution, the recipient does not need to be the offspring of the donor or even of the same species.
    • Example: Antibiotic resistance is facilitated through horizontal gene transfer.
  • Horizontal gene transfer accounts for about 20-30% of genomic variation in modern bacterial species.

Summary of Key Points

  • Evolution is characterized by heritable change in populations over generations.
  • Individual organisms do not evolve; populations do.
  • Key Concept: Natural Selection is a mechanism leading to evolution.
    • Selective pressures act on variations to favor advantageous traits, leading to a gradual change in populations over time.

Examples of Natural Selection

  • Darwin's Finches: Example of variation in beak size due to adaptation to different food sources across different islands.
  • Seahorse & Blue Dragon nudibranch: Develop adaptations such as camouflage due to natural selection.
  • Whales: Fossil records illustrate transitions from land mammals to aquatic forms, showcasing progressive anatomical changes like the reduction of hind limbs and development of the blowhole.

Homologous vs. Analogous Structures

  • Homologous Structures: Similar structures resulting from a common ancestry (e.g., bat wing, dolphin flipper, human arm).
  • Analogous Structures: Similar structures arising from convergent evolution without common ancestry (e.g., squid eye vs. human eye).

Genetics Role in Evolution

  • DNA: The hereditary material that remains stable across generations.
  • Genes: Segments of DNA that code for proteins.
  • Mutations: Changes in DNA that can affect protein functions.
    • Types: Neutral, beneficial (increase fitness), and harmful (decrease fitness).