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Evolution
Chapter 6
Pre-Darwinian Theories
http://anthro.palomar.edu/evolve/evolve_1.htm
Darwin’s Voyage
 Where
did he go and why?
 5 year trip around the world on the
HMS Beagle in 1831
 To learn about living things as the
ship’s naturalist
 Saw many living things different
from life in England
H.M.S. Beagle
A Brief Biography of
Charles Darwin
Darwin's Observations
 Amazed
by the diversity of life
 Large sloth & armadillo bones in
Argentina
 Diversity in the Galapagos Islands
 Species: a group of similar
organisms that can mate with each
other and produce fertile offspring
Similarities and Differences
How did Darwin think plants and animals
had originally come to the Galapagos
Islands?
He inferred:
 Blown out to sea during a storm
 Adrift on a fallen log
 Reached the islands, reproduced
 Offspring eventually became different
from mainland species
 Species differed island to island

Adaptations
Adaptation:
a trait that helps
an organism survive and
reproduce
Tortoises’ shells
Finch beaks
Adaptations are controlled by
genes!
Disney Imagineering
Take Some Notes About
Animal Adaptations That help Them
Specifically:
Communicate!
• Elephants
• Dolphins
• Naked Mole Rats
• Meerkats
For Example:
WITH NO
THUMBS YOU
COULDN’T….
Adaptations
New Adaptation?
Nothing Works All The Time!
Darwin’s “Dangerous” Idea
 Perhaps
the species became better
adapted to the new conditions
 He did not know how it happened
 Thought it might be similar to
selective breeding
 evolution: gradual change in a
species over time
Artificial Selection
“Selective Breeding”
Artificial Selection Myth?
Samurai crab, H. japonica and stylized Kabuki samurai face
Natural Selection
 Explanation
proposed by Darwin and
Alfred Russel Wallace about how
evolution occurs
 Process by which individuals better
adapted to environment are more
likely to survive & reproduce
 Factors: overproduction –
competition – variations - selection
Overproduction
 Most
species produce more
offspring that can survive
 Not enough resources available
for all: food; water; space
 Ex: sea turtles – many are born
but few survive
 Darwin wondered why?????
Adult female Sea Turtles return to the
beach where they were born to lay up to
200 soft-shelled eggs in the sand. When
the baby turtles hatch, they immediately
head for the nearby water. Many young
turtles are eaten by birds and other
predators during this difficult trip. It has
been estimated that only 1% of these
hatchlings will reach adulthood. No one
knows how the females find the beach
where they were born.
Variations
 Difference
between individuals of
same species
 Genetic!
 EX: some turtles are faster than
others
 Could help them survive
•Happy Face Spiders
•look different, but can interbreed
•they are the same species: Theridion grallator.
Variations in the Species!
Adaptation/Competition
Indirectly
for available
resources
Not usually physical
Ex: some turtles don’t find
food
Some don’t escape predators
Selection
Some variations = better adapted
 More likely to reproduce
 Offspring may inherit helpful alleles
 More individuals have trait after many
generations
 ENVIRONMENT does the “selecting”
 Natural selection can lead to evolution
over a long period of time
 Ex: many faster turtles

Natural Selection
The Role of Genes in Evolution
Darwin
knew nothing of
genes or mutations
He could not explain how
traits were passed on
Now: Only inherited traits are
acted upon by natural
selection
Evolution in Action
 1977
study on Daphne Major
 Little rain led to fewer plants
 Fewer plants = fewer seeds
 Finches ate large, tough seed pods
 Many small-beaked finches did not
survive drought
 Next year = more finches with
larger, stronger beaks
Evolution in Action
 Peppered
moths of England
How Do New Species Form?
 Geographic
isolation
 A group of individuals remains
isolated long enough to evolve
different traits
 Ex: Kaibab & Abert squirrels
Kaibab Squirrel
Abert Squirrel
The Kaibab squirrel
is isolated in the
Kaibab Plateau.
South of the canyon
and elsewhere, the
similar Albert
squirrels may be
found.
How Do New Species Form?
•isolation = when some
members of a species are
cut off from the others
•a new species can form when a
group of individuals remains
separated from the rest of his
species long enough to evolve
different traits
How Do New Species Form?
Continental Drift
 As
continents separated species
became isolated
 Began to evolve independently
 Australia and the marsupials and
monotremes
Continental Drift
Pangaea &
Continental
Drift
Pangea