Download Evolution

Theory of Natural Selection:
Darwin’s explanation for
HOW evolution works.
VOYAGE OF THE HMS BEAGLE : 1831 - 1836
7 Steps to Natural
Selection
4. Struggle for existence-
1. Overpopulation
competition for water, food, &
(overproduction)shelter
animals produce more
of the fittest- the
offspring than survive. 5. Survival
best adapted & strongest tend
to survive longer & produce
2. Variation- animals of
more offspring
the same species are
6. Inheritance- favored/best
different
fit/selected variations
3. Change in
(characteristics) are passed on
to offspring.
environment7. New species arise- “selected”
a) Biological - food,
individuals grow in number
predators, shelter, etc.
and become a new species
that cannot reproduce with
b) Physical…water,
original species
oxygen, temp, etc.
Darwin’s Observation: 13 or so species of finches on different
Galapagos islands; these finches resembled the South American
(mainland) finches more than say finches in Asia….
Same process for other
species!
Jean Baptiste Lamarck: the outcaste!
 used the fossil record as evidence
 proposed a theory of evolution
where organisms became better
and better
 Mechanism - ”use” and “disuse”
leads to:
 inheritance of acquired
characteristics (you ‘acquire’ a
phenotype in your lifetime and
pass it on to your kids)
 also means environmental
influences can be inherited
 DON’T BE LAMARCKIAN!
Hugo DeVries & Mutation
Theory
• New Characteristics suddenly appear
– Mutation
• These can be passed on and may or
may not help a species become more fit
• Helped to modify Darwin’s Theory
Evidences for Darwin’s
theory
•
•
•
•
Fossil record - horse lab
Homologous Structures
Vestigial structures
Artificial selection
•
Natural selection in action: the evolution of insecticide-resistance occurs in
nature - individuals with the best fit genes that can resist the insecticide will
survive….
Fig. 22.12
B) HOMOLOGIES –
• Similarities in characteristics
resulting from common ancestry is
known as homology.
• 1) Homologous Structures: Same
skeletal elements, but different
functions
Human hand, cat limb, whale flipper, bat wing - they all
have the same basic bone structure and design; So they
have ALL evolved
a common ancestor with
B)from
HOMOLOGIES
– a similar
‘limb design’.
HOMOLOGOUS STRUCTURES
C) Vestigial organs, structures that are not used,
but which had important functions in ancestors still retained in descendents, so
evolution/change has occurred.
Some Alleged Vestigial Organs in Man
Tonsils
Coccyx (tail bone)
Thymus
Little toe
Nipples on males
Nodes on ears "Darwin's
points"
Pineal gland
Adenoids
Nictitating membrane of
eye
Appendix
Wisdom teeth
Parathyroid
Ear muscles for wiggling
Body hair
C) Vestigial organs – spurs in snakes, hind
leg bones in whales.
Artificial Selection
• Artificial Selection: The selective
breeding of domesticated plants and
animals to encourage the occurrence of
desirable traits.
• Short period of time needed for Artificial
Selection
Heredity: Characteristics that are
passed down to offspring
Mutations: Changes that occur in the
hereditary material
Mutant: The new form that survives a
mutation and passes this trait on to
offspring
Adaptation: A favorable variation
within a species that may help an
organism survive
• Natural selection Predators/famine/space
shortage/disease/
environmental changes
Origin of life and Stanley
Miller’s Experiment
Abiotic synthesis of organic monomers
• Stanely Miller - simulated conditions on early
Earth (no oxygen, reducing environment with
inorganic gases like H2, CO2, NH3, CH4;
lightning/UV with no ozone. Favored the
synthesis of organic compounds from
inorganicmaterial
The Miller-Urey
experiments produced
a variety of amino
acids and other
organic molecules
(monomers).