Download Darwin`s Theory of Evolution

Darwin’s Theory of Evolution
Historical Context (early 1800s)
• Aristotle, Judeo-Christian culture,
book of Genesis…
–The earth is only 6000 years old
–All living species are “static” (put
here ‘as is’)
Pre-Darwin
• Lamarck (early 1800s)
• Buffon
• Inheritance of Acquired
Characteristics
Inheritance of Acquired Characteristics
• Why do giraffes have long
necks?
Because they stretch them
during their lifetime, then
their offspring have long
necks
The theory of “Use & Disuse”
Who was Darwin?
• Surgeon in training
• Minister
• Recruited by captain of HMS
Beagle
• Set sail in 1831 at the age of 22
Not just the Galapagos…
Not just finches…
Darwin made 3 main observations…
• 1. Members of a population vary in their
physical traits.
• 2. Many physical traits are inherited from
parent to offspring.
• 3. All species are capable of reproducing more
offspring than the environment can support.
And drew 2 conclusions:
• 1. Individuals who inherit traits that give
them a better chance of surviving tend to
leave more offspring than other individuals
• 2. This unequal reproduction of offspring
causes ‘favorable’ traits to accumulate in a
population over generations.
(“survival of the fittest; struggle for existence)
• Darwin called these
conclusions “Descent with
Modification”
• We call it “Natural Selection”
Important!!
• What is ‘favorable’ in one
environment may not be in another
environment.
• The environment determines what is
favorable and unfavorable.
4 Take-home Points about Natural
Selection
• 1. Individuals DO NOT evolve.
Evolution refers to generation-togeneration changes in a population.
• 2. Natural selection can only amplify
or diminish traits that are
inheritable.
4 Take-home Points about Natural
Selection
• 3. Evolution is NOT goal-directed.
No notion of “perfect species.”
Environmental factors vary in place &
time…’favorable’ traits will also vary.
4 Take-home Points about Natural
Selection
• 4. Evolution is about compromise.
It’s all about timing…
• Darwin formulated his idea of
natural selection in the early 1840s.
• He did not publish them until 1858.
Alfred Wallace