DARWIN 2012CHAPTER 10.1-3

Darwin’s voyage provided insight on evolution.

Darwin’s Observations• Darwin observed variation (difference in a physical

trait) among species.– Galápagos tortoises that live in areas with tall plants

have long necks and legs.

– Darwin noticed that the finches’ beaks seemed to be specific to their diet. Example: Galápagos finches that live in areas with hard-shelled nuts have strong beaks.

Darwin’s Observations• Observations of variations,

especially from island to island led Darwin to believe that species somehow adapt to their environment.– An adaptation is a feature that

allow an organism to better survive in its environment.

– Adaptations can lead to genetic change in a population.

• Darwin noted that traits of domesticated animals can be changed or “selected” by artificial selection (the process by which humans select traits through breeding).

neck feathers

crop

tail feathers

• Darwin proposed that the environment could “select” the best traits for the organisms within it. – Natural selection, “survival of the fittest,” is a

mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.• Fitness is the measure of survival ability and ability to

produce more offspring.• Darwin proposed that adaptations arose over many

generations.

• There are four main principles to the theory of natural selection.– variation

– overproduction– adaptation– descent with modification

VARIATIONOVERPRODUCTIONADAPTATION

• If an environment changes species with the most advantageous variation will live and the ones who don’t will die out

• Natural selection can act only on traits that already exist.• Structures can take on new functions in addition to their

original function. (Example: the panda wrist bone acts like a thumb.)

wrist bone

five digits