Darwin, Wallace & Lamarck

• Jean-Baptiste Lamarck's early theory of evolution suggested that organisms could acquire new traits during their lifetime, and that these traits could be passed to their offspring.
• According to Lamarck's theory, giraffes have long necks because:

  1. Giraffes started with short necks adapted to lower vegetation.
  2. They stretched their necks to reach higher branches for food, resulting in longer necks during an individual's lifetime.
  3. This acquired longer neck trait was passed to offspring, and successive generations have longer necks for reaching higher branches.
• Lamarck's theory was proven incorrect by modern genetics:

  We now know that characteristics acquired by an organism during its lifetime do not affect the DNA sequence of the organism, and cannot be passed down from one generation to the next. 
• Charles Darwin made a number of important observations:

  1. Individual organisms within a species show a wide range of variation for a specific trait.
  2. Darwin observed variations between species adapted to different environments.
  3. Older layers of rock contained fossils of less complex organisms, while more recent layers showed more complex organisms.
• According to Darwin and Wallace's theory, giraffes have long necks because:

  1. Some giraffes had longer necks than others, due to variation within the species.
  2. Giraffes with longer necks were better adapted to their environment, as they could eat leaves from taller trees.
  3. Giraffes with longer necks had a higher chance of surviving and reproducing, and passed on the trait of long necks to their offspring.
  4. Over many generations, this process produced modern giraffes, with very long necks.
• It took time for the theory of evolution to become widely accepted

  Many people didn't accept Darwin and Wallace's theory, for several reasons:

  • Religious reasons 
  • Darwin's theory challenged the religious belief that God created all life forms.
  • Lack of evidence - a lack of hard evidence made many scientists hesitant to accept Darwin & Wallace's theory.
  • DNA hadn't been discovered yet the mechanism for inheritance and variation, now understood through genetics, was unknown during Darwin's time.