Evolution part 1

• 250 years ago, no one knew Earth's age
• Scientists learned that Earth is millions of years old (or older), but many believed that a creator made all species in their present form
• Today's scientists, relying on a wide range of evidence, accept evolution as the explanation for life's diversity
• Evolution


  Descent with modification
• Descent


  Inheritance
• Modification


  Changes in traits from generation to generation
• Evolution occurs in a population


  Biologists say that evolution occurs in a population when some alleles become more common, and others less common, from one generation to the next
• Evolution


  Genetic change in a population over multiple generations
• Gene pool


  Entire collection of genes and their alleles
• Evolution


  A change in allele frequencies
• Because an individual's alleles do not change, evolution occurs in populations, not individuals
• Human populations originating in different regions of the world have unique allele frequencies
• Blond hair, blue eyes (European countries)

  • Darker color (Asian continent)
• Aristotle recognized that all organisms are related in a hierarchy of simple to complex forms, but he believed that all members of species were created identical to one another
• This idea influenced scientific thinking for nearly 2000 years
• "Special creation"


  Sudden appearance of organisms on Earth
• People believed that this creative event was planned and purposeful, that species were fixed and unchangeable, and that the Earth was relatively young
• Georges-Louis Buffon


  Suggested that closely related species arose from a common ancestor and were changing
• Jean Baptiste de Lamarck


  Proposed the first scientifically testable evolutionary theory, reasoning that organisms that used one part of their body repeatedly would increase their abilities, and disuse would weaken an organ until it disappeared
• Lamarck surmised (incorrectly) that these changes would pass to future generations
• With these new theories and ideas, people were beginning to accept the theory of evolution but DID NOT yet understand how it could result in the formation of new species