What is Biology?

• Biology is the study of life and living organisms.
• All living things share five fundamental traits:
  1. Cells: All organisms are made of membrane-bound cells.
  2. Replication: All organisms reproduce.
  3. Evolution: Populations evolve over time.
  4. Information: Genetic information is encoded in DNA.
  5. Energy: Organisms acquire and use energy.

Cell theory

• Developed by Schleiden, Schwann, and Virchow.
• Two main tenets:
  • All organisms are made of cells.
  • All cells come from preexisting cells.
• Implies a common ancestry among all life forms.

Theory of Evolution by Natural Selection

• Proposed by Darwin and Wallace.
• Two components:
  • Pattern: Species change over time and share common ancestry.
  • Process: Natural selection causes evolution.
• Natural selection requires:
  • Variation in traits.
  • Heritability of traits.
  • Differential reproductive success.

Chromosome Theory of Inheritance

• Genes are located on chromosomes.
• DNA is the molecule of heredity.
• Central Dogma: DNA → RNA → Protein.

Tree Of Life

• Phylogenetic tree shows evolutionary relationships.
• Three domains:
  • Bacteria
  • Archaea
  • Eukarya
• Based on ribosomal RNA sequences.

Scientific Method

• Steps: Observation → Hypothesis → Experiment → Analysis → Conclusion.
• Hypotheses must be testable and falsifiable.
• Controlled experiments isolate variables.

Darwin & Wallace’s Contributions

• Proposed that species change over time and share common ancestry.
• Introduced population thinking: variation among individuals is key.
• Evolution is a scientific theory—testable and supported by evidence.

Historical Context

• Plato: Typological thinking—species are fixed and perfect.
• Aristotle: Scale of Nature—species arranged by complexity.
• Lamarck: Species evolve by moving up the scale; traits acquired during life are inherited

Evidence for Evolution

• Fossil Record: Shows changes over time and transitional forms.
• Law of Succession: Extinct species resemble living species in the same area.
• Transitional Features: Traits in fossils that are intermediate between ancestral and derived forms.
• Vestigial Traits: Reduced or nonfunctional traits inherited from ancestors.

• Homology: Similar traits due to shared ancestry.
  • Genetic homology: Similar DNA sequences.
  • Developmental homology: Similar embryonic development.
  • Structural homology: Similar body structures.
• Artificial selection demonstrates how traits can change under selective pressure

Mechanism of Natural Selection

• Individuals with advantageous traits reproduce more.
• Over generations, these traits become more common.
• Evolution occurs in populations, not individuals.

Misconceptions Clarified

• Evolution is not goal-directed.
• Individuals do not evolve—populations do.
• Natural selection does not give organisms what they “need.