Evolutionary Theories: Lamarck's Contribution

Key Figures and Their Theories

Jean-Baptiste Lamarck (1744-1829)

• Believed evolution occurs through natural laws, driven by two forces:
  • One force drives organisms up a ladder of complexity
  • Another force adapts organisms to local environments through use and disuse of characteristics
• Inheritance of Acquired Characteristics:
  • Frequent use of an organ strengthens and enlarges it
  • Disuse weakens it
  • Acquired traits are passed to the next generation
• Example: Giraffes' necks lengthening over generations from reaching high leaves

Thomas Robert Malthus (1766-1834)

• Focused on population growth and resource limitations
• Key idea:
  • Populations grow until resource limits are reached
  • Resource availability influences population size
• Human factor:
  • Struggle for existence based on cost-benefit decisions in sex, work, and children
• Influenced Darwin's application to plants and animals, noting competition for resources within and between species

Sir Charles Lyell (1797-1875)

• Geologist and Uniformitarianism theorist
• Natural processes in the past are the same as those today
• Earth's features formed through small changes over long periods
• Rejected Lamarck's use and disuse theory, suggesting centers of creation instead
• Influenced Darwin by supporting long-term change ideas and encouraging him to publish "On the Origin of Species"

Charles Darwin (1809-1882)

• Traveled on the HMS Beagle, studying geology, fossils, and organisms
• Influenced by Malthus' theory on population growth vs. resource competition
• Theory: Natural Selection
• Favorable traits are preserved, while unfavorable ones are destroyed
• Led to the evolution of new species over time from common ancestors
• Published "On the Origin of Species" (1859), providing a logical explanation for the diversity of life
• Favorable heritable traits become more common in successive generations, while unfavorable traits become less common