Themes of Biology and Evolution: Study Notes

Chapter 1: Themes of Biology and Evolution

Major Themes in Biology

• Organization: Biological systems are structured in a hierarchy, from molecules to the biosphere. Emergent properties arise at each level due to the arrangement and interactions of parts.

• Information: Life processes depend on the transmission and expression of genetic information, primarily through DNA.

• Energy and Matter: Living organisms require energy to grow, reproduce, and maintain organization. Energy flows through ecosystems (e.g., sunlight to chemical energy), while chemicals cycle within them.

• Interactions: Organisms interact with each other and their environment, leading to feedback mechanisms such as negative feedback (e.g., regulation of blood glucose).

• Evolution: The process by which populations change over time, explaining both the unity and diversity of life.

Cell Types and Genetic Information

• Eukaryotic cells: Contain membrane-bound organelles, including a nucleus (e.g., plants, animals, fungi, protists).

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles (e.g., bacteria, archaea).

• DNA: The molecule that stores genetic information; transmitted from parent to offspring.

Producers vs. Consumers

• Producers: Organisms (usually plants and algae) that convert energy from sunlight into chemical energy via photosynthesis.

• Consumers: Organisms that obtain energy by eating other organisms.

Feedback Regulation

• Negative feedback: A process in which a system responds to a change by returning to its original state (e.g., body temperature regulation).

Climate Change

• Caused by increased greenhouse gases, leading to global temperature rise and ecosystem impacts.

Domains of Life

• Three domains: Bacteria, Archaea, and Eukarya.

Scientific Inquiry

• Inductive reasoning: Drawing general conclusions from specific observations.

• Deductive reasoning: Making specific predictions based on general principles.

• Hypothesis: A testable explanation for an observation.

• Theory: A broad explanation supported by a large body of evidence.

• Variables: Independent variable is manipulated; dependent variable is measured.

Chapter 22: Natural Selection

Foundations of Evolutionary Theory

• Charles Darwin: Developed the theory of evolution by natural selection.

• Natural selection: The process by which individuals with advantageous traits survive and reproduce more successfully.

• Evolution: Change in the genetic composition of a population over generations.

• Unity and diversity of life: Explained by descent with modification from common ancestors.

Historical Context

• Paleontology: Study of fossils; Cuvier contributed to understanding extinction.

• James Hutton & Charles Lyell: Proposed gradual geological changes over time (uniformitarianism).

Key Concepts in Natural Selection

• Adaptations: Inherited traits that enhance survival and reproduction.

• Descent with modification: Species change over time, giving rise to new species.

• Artificial selection: Humans select for desirable traits in organisms (e.g., dog breeding).

• Darwin’s Observations:

  • 1. Members of a population vary in inherited traits.

  • 2. All species can produce more offspring than the environment can support.

• Darwin’s Inferences:

  • 1. Individuals with advantageous traits leave more offspring.

  • 2. Favorable traits accumulate in the population over generations.

• Allele frequency: Proportion of a specific allele among all alleles in a population.

• Populations evolve, not individuals.

Evidence for Evolution

• Direct observations: e.g., antibiotic resistance in MRSA.

• Homology: Similarity due to shared ancestry (e.g., mammal forearm bones).

• Vestigial structures: Remnants of features that served a function in ancestors.

• Convergent evolution: Independent evolution of similar features in different lineages (e.g., wings in bats and birds).

• Analogous traits: Similar function, different ancestry.

• Homologous traits: Similar ancestry, may have different functions.

• Biogeography: Geographic distribution of species.

Chapter 23: Evolution of Populations

Mechanisms of Evolution

• Four mechanisms:

  • Natural selection

  • Genetic drift

  • Gene flow

  • Mutation

• Microevolution: Change in allele frequencies within a population.

• Macroevolution: Broad patterns of evolutionary change above the species level.

Genetic Variation

• Mutation: Source of new alleles; can be beneficial, neutral, or harmful.

• Types of mutations: Point mutations, insertions, deletions, duplications.

• Sexual reproduction: Increases genetic variation through recombination.

Hardy-Weinberg Principle

• Describes a non-evolving population; allele and genotype frequencies remain constant.

• Equation:

  • $p^2 + 2pq + q^2 = 1$

  • $p + q = 1$

• Where p and q are the frequencies of two alleles.

Genetic Drift

• Random changes in allele frequencies, especially in small populations.

• Founder Effect: A few individuals establish a new population (e.g., island colonization).

• Bottleneck Effect: Population size is drastically reduced, leading to loss of genetic diversity (e.g., cheetahs).

Gene Flow

• Movement of alleles between populations, reducing differences among populations.

Natural Selection and Adaptive Evolution

• Relative fitness: Contribution to the gene pool relative to others.

• Directional selection: Favors one extreme phenotype (e.g., larger beaks in finches).

• Stabilizing selection: Favors intermediate phenotypes (e.g., human birth weight).

• Disruptive selection: Favors both extremes over intermediates.

• Adaptations: Traits that increase fitness in a given environment.

• Sexual selection: Selection for traits that increase mating success.

• Environmental changes can impact selection pressures.

Chapter 24: Origin of Species

Speciation and Species Concepts

• Speciation: The process by which one species splits into two or more species.

• Biological species concept: Species are groups of interbreeding populations that are reproductively isolated from others.

Reproductive Isolation

• Prezygotic barriers: Prevent fertilization.

  • Habitat isolation: Populations live in different habitats (e.g., land vs. water).

  • Temporal isolation: Breed at different times (e.g., spring vs. fall).

  • Behavioral isolation: Different mating behaviors (e.g., bird songs).

  • Mechanical isolation: Physical differences prevent mating.

  • Gametic isolation: Sperm and egg are incompatible.

• Postzygotic barriers: Prevent hybrid offspring from developing into viable, fertile adults.

  • Reduced hybrid viability: Hybrids do not develop properly or are frail.

  • Reduced hybrid fertility: Hybrids are sterile (e.g., mule).

  • Hybrid breakdown: Offspring of hybrids are weak or sterile.

• Limitations: Some species do not fit the biological species concept (e.g., asexual organisms, fossils).

Modes of Speciation

• Allopatric speciation: Populations are geographically separated.

• Sympatric speciation: Occurs without geographic separation (e.g., cichlid fish in African lakes).

Hybrid Zones

• Regions where different species meet and mate, producing hybrids.

• Outcomes over time:

  • 1. Reinforcement: Strengthening of reproductive barriers.

  • 2. Fusion: Weakening of barriers, species merge.

  • 3. Stability: Continued production of hybrids.

• Punctuated equilibria: Long periods of stability interrupted by brief periods of rapid change.

Chapter 25: History of Life on Earth

Macroevolution and Early Earth

• Macroevolution: Evolutionary change above the species level (e.g., origin of mammals).

• Early Earth conditions favored the formation of simple molecules and eventually life.

Fossil Record

• Types of fossils: Body fossils, trace fossils, casts, molds.

• Fossil record shows changes in life forms over time, but is incomplete due to preservation biases.

• Fossils are more likely to form for organisms with hard parts, in aquatic environments, and rapid burial.

• Dating fossils:

  • Relative dating (stratigraphy)

  • Radiometric dating (using isotopes)

Major Events in Life’s History

• First single-celled organisms: Prokaryotes, including stromatolites.

• Photosynthesis and the oxygen revolution: Led to accumulation of atmospheric O2.

• First eukaryotes: Originated via endosymbiosis (e.g., mitochondria, chloroplasts).

• Origin of multicellularity: Enabled evolution of complex organisms.

• Cambrian explosion: Rapid diversification of animal forms (~535 million years ago).

• Colonization of land: Plants, arthropods, and tetrapods moved onto land.

Plate Tectonics and Mass Extinctions

• Plate tectonics: Movement of Earth’s crustal plates; formation and breakup of Pangaea.

• Mass extinctions:

  • Permian Mass Extinction: ~252 million years ago; loss of ~96% of marine species.

  • Cretaceous Mass Extinction: ~66 million years ago; extinction of dinosaurs.

  • Sixth mass extinction: Ongoing, largely due to human activity.

• Adaptive radiation: Rapid evolution of diverse species from a common ancestor, often following mass extinctions.