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1

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.

2

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.

3

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.

4

Chromosome Theory of Inheritance

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

5

Tree Of Life

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

6

Scientific Method

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

7

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.

8

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

9

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.

10

  • 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

11

Mechanism of Natural Selection

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

12

Misconceptions Clarified

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