Transcript Do Now 9/09 Have you ever heard the term “survival of the fittest

Beginnings of Modern Evolutionary
Thought
• Charles Darwin hypothesized that species were
modified by natural selection.
• Natural Selection- organisms best suited for their
environment reproduce more successfully
• Over many generations, the proportion of
organisms with favorable traits increases in a
population.
How did Darwin Come up with his
hypothesis?
• Spent 5 years on a ship called the Beagle and
sailed around the world and made various
stops
• When the ship stopped in a new place, he
would collect specimens and keep careful
records of his observations
Darwin’s Theories
• Descent with modification- newer forms of
life are actually modified descendents of older
species
• All species had descended from one or a few
original types of life
• Based this on what he saw with the finches
from the Galapagos Islands
What other scientists influenced
Darwin?
• Thomas Malthus- studied populations
-found that populations can double or grow
exponentially
• - Darwin noticed that most populations did
not grow exponentially because
environmental factors limit growth
Because of Malthus….Darwin came up
with the following:
• Fitness- how well an organism does in an
environment defined by reproductive success
• An individual with high fitness is well adapted
to its environment and reproduces more
successfully (survival of the fittest)
-A population of organisms adapt to their
environment as their proportion of genes for
favorable traits increases
-Organisms don’t select traits, environments
do!
-If the environment changes so fast that the
organisms can’t adapt quickly enough, mass
extinctions occur.
Alfred Wallace
• He unknowingly came up with
the same theory of evolution as
Darwin
• He asked Darwin to read his findings and once
Darwin saw how similar his thoughts were to
his own he know he couldn’t put off
publishing his findings anymore.
Lamarck
• He believed that acquired traits
were passed on to offspring
• Acquired traits aren’t determined by genes,
they are something that arises during the
organism’s lifetime as a result of behavior or
experience
• Lamarck thought that a lizard that didn’t
use its tail would have offspring that
would have a smaller tail.
• He was the first to say that organisms
change over time, descending from older,
similar organisms
Lamarck’s “Use/Disuse Theory”
Charles Lyell
• Wrote a book called “Principles of Geology”
which was centered around the gradual
change of the earth
-ex: in Lyell’s book, he talked about how a
valley could have been formed by the gradual
weathering of the earth by a river
• Darwin applied this knowledge of the earth to
organisms