Natural Selection and Darwinian Evolution

Introduction to Evolutionary Biology

• Speaker background in evolutionary biology and paleontology.

• Personal anecdote: speaker experiences sciatica, impacting lecture delivery.

Natural Selection and Evolution

• Evolution: Central theme in biology along with cell theory and genetics.

  • Explains changes in organisms over time and connects all life forms that have existed.

  • Darwin introduced natural selection as a mechanism for evolution.

• Descriptive Modification: The term "evolution" wasn't used in the 18th-19th centuries; instead, changes in lineages were referred to as such.

• Encourages inquiry about organismal change and classification relation to evolution.

Historical Context of Evolutionary Ideas

• Key Figures:

  • Carolus Linnaeus: Developed binomial nomenclature, focusing on structural similarities among organisms to promote understanding of nature.

  • James Hutton: Introduced geological principles that support Earth's changes over time.

  • Jean Baptiste Lamarck: Early advocate for species change, suggesting traits could be passed on through usage and disuse (e.g., giraffes' neck stretching).

Charles Darwin's Contributions

• Darwin (1809) benefited from wealth, quality education, and naturalistic studies.

• Most significant contribution: Mechanism of natural selection.

• Voyage of the Beagle: Provided observations leading to insights on evolutionary changes, especially in the Galapagos Islands.

  • Collected fossils and specimens that shaped his ideas.

Natural Selection Defined

• Natural Selection Process: Drives adaptation of organisms based on environmental pressures.

• Key Observations Leading to Natural Selection:

  • Overproduction of offspring creates competition for limited resources.

  • Variation among individuals affects survival and reproduction chances.

  • Organisms with advantageous traits (higher fitness) are more likely to survive and reproduce, tying observations to environmental conditions.

The Concept of Fitness

• Fitness: Ability to survive and reproduce in specific environments.

  • Traits advantageous in one environment might not be in another.

  • Influenced by adaptations to environmental pressures.

Descriptive Modification Simplified

• Organisms change over time due to natural selection acting on inherited variations.

• Long-term adaptations increase species diversification (e.g., rapid variation in dog breeds via human selection versus natural selection).

Malthusian Influence on Darwin

• Thomas Malthus: His population theory influenced Darwin on competition and survival driven by resource limitations.

• Resource availability leads to population struggles affecting natural selection.

Reproductive Success and Selection Pressures

• Differential Reproduction: Not all organisms have equal offspring success.

• Galapagos Finches: Variation in beak shapes correlates with available food sources, showing adaptation and specialization over generations.

Conclusion

• Evolution through natural selection is a cornerstone in biology, explaining life's interconnectedness and adaptation processes over time.

Key Concepts from Previous Lecture

• Evolutionary change impacts individuals within a population.

• Natural selection: Organisms more likely to survive lead to more offspring.

Evolutionary Mechanisms

• Common Ancestry: Assumes a single ancestor species for fish that migrated and adapted to the Galapagos.

  • Selection Processes: Varied environments lead to different adaptations in organisms.

  • Variants: Different beak shapes evolved for specific food types (large for seeds, smaller for fruits, long for insects).

Structural Adaptation Examples

• Evolutionary changes driven by food availability and predation (e.g., coloration for camouflage).

Microevolution vs. Macroevolution

• Microevolution: Small, observable population changes (e.g., allele frequency).

• Macroevolution: Large-scale evolutionary changes over time, leading to new species.

Role of Natural Selection

• Fitness: Traits that enhance environment matching lead to better survival.

  • Artificial Selection: Human-induced trait changes in domesticated species demonstrate selective changes.

Case Studies and Examples

• Peppered Moths: Color shift pre- and post-industrialization indicating natural selection.

• Honeycreepers in Hawaii: Example of distinct adaptations similar to finches.

  • Bacterial Resistance: Rapid bacterial adaptation to antibiotics.

  • Pesticide Resistance: Similar adaptive patterns in pests from chemical exposure.

  • Camouflage in Praying Mantises: Adaptations improve survival through environmental blending.

Foundations of Evolutionary Theory

• Natural selection pressures act on existing traits.

• Only populations evolve over generations; individuals do not.

• Evolutionary theories (cell and gene) explain biological diversity.

Fossil Record as Evidence

• Fossils: Evidence of prehistoric life (bones, traces).

  • Show transitions between ancient and modern species (e.g., terrestrial ancestors to aquatic mammals).

  • Highlight vestigial structures indicating evolutionary remnants.

Conclusion

• Evolution is complex and influenced by various pressures, from microevolutionary shifts to macroevolutionary changes, enriching biological understanding through time.

In-Depth Notes on Evolutionary Evidence and Mechanisms

• Natural Selection: Process evidenced by fossil records indicating changing organisms over time.

• Functional Anatomy: Study of how structures relate to function, informing organism lifestyles.

• Transitional Series: Shows evolution from one form to another (e.g., terrestrial to aquatic mammals).

Comparative Anatomy

• Definition: Comparison of anatomical structures across species (e.g., forelimbs of various mammals).

• Homologous Structures: Similar structures due to common ancestry, showing evolutionary ties.

  • Types: Humerus, radius, and ulna across mammals and their connections through evolution.

  • Analogous Structures: Structures serving similar functions but evolved independently, indicating no common ancestry.

Classification and Evolutionary Relationships

• Utilize structural similarities and evolutionary relationships for classification (homology vs. analogy).

  • Vestigial Structures: Indicate past adaptations (e.g., whale pelvic bones).

Embryological Evidence

• Embryology reveals similarities in embryonic stages among related organisms, though misinterpretations like ontogeny recapitulating phylogeny are incorrect.

Molecular Biology and Phylogenetics

• Phylogenetic Trees: Show evolutionary relationships based on structures or genetic data, enhanced through computing advancements.

  • Genomic Changes: Relationship between genotype and phenotype, complexities in genome size and evolution.

Noncoding DNA and Functions

• Noncoding DNA comprises 75% of the human genome, regulating vital processes.

  • Transposable Elements: DNA sections that influence expression; types include transposons and retrotransposons.

Summary of Key Concepts

• Homology vs. Analogy: Distinct meanings regarding evolutionary significance and adaptation mechanisms.

• Classification: Based on shared derived characters for accurate evolutionary depiction.

Ongoing Research**: Continued molecular biology studies refine genetic relationships and evolutionary processes.

In-Depth Notes on Hardy-Weinberg and Evolutionary Change

Hardy-Weinberg Principle

• Overview: Tool to assess evolutionary change in populations, predict allele frequencies.

• Equilibrium Conditions: Strict conditions for Hardy-Weinberg equilibrium (e.g., large sizes, no mutations, random mating).

  • Real-World Impact: Natural populations rarely achieve this equilibrium due to frequent violations.

Agents of Change

• Natural Selection: Differentiates survivability based on traits affecting fitness, leads to frequency increases of advantageous traits.

• Genetic Drift: Random changes impacting allele frequencies, particularly in small populations (bottleneck and founder effects).

• Gene Flow: Movement between populations changing frequencies, can quickly alter genetic diversity.

• Non-Random Mating: Alters allele frequencies through selective mate preference.

Types of Natural Selection

• Stabilizing Selection: Favors intermediates, promotes uniformity.

  • Example: Pocket mice in a homogenous habitat.

• Directional Selection: Favors one extreme, shifting population traits.

  • Example: Dark-colored pocket mice favored in post-fire landscapes.

• Disruptive Selection: Favors extremes leading to potential speciation.

  • Example: Mice adapting to both light and dark habitats.

Variation Maintenance Mechanisms

• Mutation: Source of new alleles for variability.

• Heterozygote Advantage: Higher fitness in heterozygous individuals (e.g., sickle cell trait).

• Sexual Selection: Leads to sexual dimorphism through distinct mating pressures.

Conclusion

• Natural selection usually decreases variation while mutations and gene flow can introduce new alleles.

• Isolation and differing pressures promote significant evolutionary changes, potentially resulting in new species.

Speciation

Barriers to Reproduction

• Biological Species Concept: Defines species based on reproductive viability (or lack thereof).

Prezygotic and Postzygotic Barriers

• Prezygotic Barriers: Prevent fertilization through various mechanisms (e.g., habitat, temporal, behavioral).

• Postzygotic Barriers: Affect offspring post-fertilization (e.g., hybrid viability, fertility).

• Limitations: Not applicable to fossils or asexual organisms.

Species Concepts

• Morphological Species Concept: Structural features used for identification in paleontology.

• Ecological Species Concept: Focused on interactions with environments.

• Phylogenetic Species Concept: Based on shared derived characteristics.

Modes of Speciation

1. Allopatric Speciation: Geographic isolation changes genetic diversity.

2. Sympatric Speciation: Occurs without isolation (e.g., polyploidy, habitat differentiation).

Complex Factors

• Environmental changes may reintroduce formerly isolated populations.

Rates of Speciation

• Varies considerably; two models - gradualist and punctuated equilibrium characterize trends.

Genetic Changes in Speciation

• Number of changes for speciation differs; single gene changes causing reproductive incompatibilities illustrated.

Detailed Study Notes on Macroevolution

Introduction to Macroevolution

• Transitioning to macroevolution, focusing on larger-scale changes beyond species.

• Key events include the first prokaryotic cells, eukaryotic development, and mass extinctions affecting speciation.

Formation of the Solar System

• Nebular Hypothesis: Solar system forms from a rotating gas-cloud, explaining planet material differences.

Earth's Structure

• Earth consists of 3 layers: Inner Core, Outer Core, and Mantle; tectonic movements create geological processes.

Plate Tectonics

• Plate Boundaries: Divergent, Convergent, and Transform movements impacting geology and biodiversity.

Continental Drift Hypothesis

• Suggests continent migrations influence evolution through fossil evidence affirming shared ancestry across divided landmasses.

Early Environment and Life

• Earth’s initial atmosphere and conditions favorable for life formation evolved over billions of years.

Origin of Life

• Early Earth Conditions: Recreated in experiments, leading to insights on organic compound formations.

Steps to Life Formation

1. Abiotic synthesis of organic molecules.

2. Macromolecule formation.

3. Protocell formation.

4. Origin of self-replicating molecules.

Role of RNA

• RNA’s self-replicating capability makes it pivotal in early life processes.

Extraterrestrial Origins of Organic Molecules

• Meteorites contributing organic materials highlight potential life's origins.

Understanding Early Cellular Life

Evidence of Early Life Forms

• Stromatolites: Earliest fossils comprising sediment and bacteria, leading to domain classifications.

Metabolic Processes of Early Cells

• Anaerobic processes in early cells included fermentation and chemolithotrophy.

Development of Photosynthetic Organisms

• Cyanobacteria emerged, significantly contributing to Earth's oxygen.

Geological Evidence Supporting Oxygen Evolution

• Bands of oxidized/unoxidized iron demonstrate past environmental changes with oxygen accumulation.

Evolution of Eukaryotic Cells

• Fossil evidence and hypotheses support eukaryotic origins via membrane infolding and endosymbiosis.

Advantages of Eukaryotic Cell Structure

• Increased efficiency through internal membranous organelles aids organism complexity.

Evolution of Multicellularity

• Support via fossil records detailing transitions from unicellular to multicellular life.

Timeline of Life Events

• Key geological timelines highlighted for the evolution of life forms across billions of years.

Cambrian Explosion

• An increase in diversity representing the beginnings of modern animal phyla within complex ecosystems.

Summary of Macroevolution

• Emphasizes patterns observed in evolution over time, correlating with significant geological and environmental changes, thus contributing to the biodiversity we observe today.