Download 15.3 Darwin Presents His Case

15.3 Darwin Presents His
Case
Darwin Presents His Case
• The specimens Darwin brought back had
the scientific community in a buzz
• Learned that Galapagos species are
found nowhere else in the world
• They looked similar to South American
mainland species but were clearly
different
Darwin’s Book
• Published his ideas about
species diversity and
evolution in On the Origin of
Species
• Proposed a mechanism for
evolution called natural
selection
• Many agreed with Darwin
while others strongly
opposed him
Natural Variation
• Scientists used to believe species were
perfect and unchanging
• Darwin argued natural variation
(differences among species) is found in all
types of organisms
– Some cows give more milk
– Some plants give larger fruit
Artificial Selection
• Darwin also studied English
farmers and breeders
• Used selective breeding to breed
the “best” individuals
– Largest hogs, fastest horses
• Darwin called this artificial
selection
• Still used today!
Evolution by Natural Selection
• Darwin believed that evolution occurred
through natural selection
• Natural selection = the process by which
only the organisms best adapted to their
environment will survive and reproduce
• 3 main parts to natural selection
1. The Struggle for Existence
• There are more living
things than resources
• Results in competition
• Competition = the
struggle among living
things to get their
needs for life
2. Survival of the Fittest
• Individuals that are better suited to their
environments survive (high fitness)
• Individuals not suited to their environment
will die (low fitness)
• Fitness – the ability of an individual to
survive and
reproduce in
its environment
– Is a result of
adaptations
2. Survival of the Fittest
• Adaptation – any inherited characteristic
that increases an organism’s chance for
survival
– Long necks in giraffes
– Long toes / webbed feet
in birds
– Coloring / Camouflage
3. Descent with Modification
• Each living species has descended, with
changes, from other
species over time
• Implies all organisms
are related to one
another
– Known as common
descent
Evidence for Evolution
• Fossil Evidence
– When living things from the past are
compared to living things today, we can see
that change has occurred
Evidence for Evolution
Beaver
Beaver
NORTH
AMERICA
Muskrat
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Capybara
SOUTH
AMERICA
Coypu
Coypu and
Capybara
• Geographic distribution
of living things
– Species are located in
different parts of the
world but share
similarities
– Beavers and capybara
are similar
– Muskrat and coypu are
similar
Evidence for Evolution
• Homologous body structures
– Limbs (arms, wings, legs, flippers) have
different form and function but are
constructed from the same bones
Turtle
Alligator
Typical primitive fish
Bird
Mammals
Evidence for Evolution
• Vestigial structures
– Body parts that no longer have
functions
– i.e. Pink lump in corner of eye
• Remnant of a third eyelid
• Frogs and turtles have third eyelid
to see underwater
– Appendix
• In many mammals the appendix is
used to help digest food
Evidence for Evolution
• Embryology
– Studying embryo
development to
look for similarities
and differences