7.2 Darwin’s Theory

• Darwin was encouraged to publish his work, because in 1858 Alfred Wallace was coming up with similar conclusions
• A year later Darwin published “The Origin of Species”
• 1844, Darwin outlined his “ideas”, but didn’t release it to the public, wanted more evidence
• Origin of Species:

  1. All species of organisms living on Earth today are descended from ancestral species (i.e. species evolve over time)
  2. The mechanism that causes species to change over time is Natural Selection
• Early organisms spread into various

  habitats over millions of years.
• In the different habitats, they accumulated different modifications or adaptations to create diverse ways of life.
• Darwin used the term “descent with

  modifications” not “evolution”.
• Natural Selection exists because of:

  1. Struggle for existence
  2. Variation
  3. The Role of the Enviroment
• The Struggle for Existence: All species tend to produce excessive numbers of

  offspring. More individuals being produced than an environment can

  support leads to struggle.
• Variation: Refers to differences amoung members of the same species.

  • Certain variations that suited the environment were more likely to be passed onto offspring
• The Role of the Environment: The environment selects from organisms with variations that are best suited for that environment (e.g. Lamarck’s giraffes)
• Natural Selection: Process by which individuals with inherited characteristics well suited for their environment leave more offspring on

  average than do individuals with adaptations less suited to

  the environment
• Fitness: The ability of an individual to survive and reproduce in it’s environment
• Evidence for Evolution:

  1. The Fossil Record
  2. Geographic Distribution
  3. Comparative Anatomy
  4. Comparative Development
  5. Molecular Biology
• The Fossil Record: The record of past life forms preserved in rocks.
• Geographic Distribution: The distribution of a species in a particular area.
• Comparative Anatomy: Study of the similarities and differences between organisms.
• Homologous Structures: Structures that are similar in structure but not function.
• Analogous Structures: Structures that have similar functions but are not identical.
• Vestigial Structures: Structures that are no longer used but are still present in the body.
• Comparative Development: The study of the differences in the development of countries and their people.
• Molecular Biology: The study of the structure and function of molecules and their interactions.
• Artificial Selection: The process by which humans selectively breed organisms to produce desired characteristics.
• Antibiotic Resistance in Bacteria:

  • Bacteria have many variations
  • Many people don’t take their full prescription
  • Drug-resistant bacteria are able to survive due to N.S. and reproduce and become more common