Download Darwin and Natural Selection PPT Lecture

Chapter 22
Descent with Modification: A
Darwinian View of Life
(PART 1)
Ms. Gaynor
AP Biology
Darwin made two major
points in his book called
Origins of Species:
1. Many current species are
descendants of ancestral
species
2. Natural selection is a
mechanism for this
evolutionary process
Resistance to the Idea of
Evolution
• The Origin of Species = Darwin’s book
–Shook the deepest roots of Western
culture
–Challenged a worldview that had
been prevalent for centuries
• Earth ONLY ~6000 yrs old
• It was unchanging!!!!
Nature and Classification of Species
• Greek philosopher Aristotle
– organisms were perfectly formed and adapted to
the world (fixed and unchanging)
• Old Testament
– Species individually designed by God and perfect
• Carolus Linnaeus
– Saw adaptations as evidence that a Creator had
designed each species for a specific purpose
– founder of taxonomy (biology concerned with
classifying organisms) & binomial
nomenclature (scientifically naming
organisms- Genus species)
Fossils, Cuvier, and
Catastrophism
• The study of fossils helped to lay
the groundwork for Darwin’s ideas
• Fossils
• remains or traces of organisms from
the past, usually found in
sedimentary rock, which appears in
the layers or strata
• Paleontology
• study of fossils
• developed by French
scientist Georges
Cuvier
• Cuvier advocated
catastrophism
• species disappear due to a
catastrophic event of earth’s
crust (volcano, earthquake…)
Hutton’s Theory of Geological
Change
• Changes in
Earth’s crust due
to slow
continuous
processes
• Idea Known as
Gradualism
Charles Lyell
Proposed theory of
Uniformitarianism
Geological processes
at uniform rates
building & wearing
down Earth’s crust
Proposed that the
Earth was millions of
years instead of a few
thousand years old
Lamarck’s Theory of
Evolution (1809)
• Lamarck hypothesized species
evolve through
• use and disuse and
• inheritance of
acquired traits
• The mechanisms he proposed
are unsupported by evidence
Lamarck’s Theory of Evolution
• Idea called Law of
Use and Disuse
• If a body part
were used, it got
stronger
• If body part NOT
used, it
deteriorated
s
• Will his
kids be
born with
big
muscles
because
he has
them?
WILL THE OFFSPRING BE NICELY PRUNED?
Principles of Populations
• Thomas Malthus (1798)
– Studied moths and natural
selection
• Capacity to over-reproduce is
seen in all species
• Eventually populations stop
increasing in size and reach a
steady state (carrying
capacity)
Charles Darwin
• LOVED nature
• Sails on HMS Beagle at 22 and
voyaged around world
• Noted flora and fauna on islands
off of South America
• Contributions of Lyell, Hutton and
Malthus lead him to his
mechanism for evolution
• species change through
natural selection
•
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
The Voyage of the Beagle
• Collected specimens of South American
plants and animals
• Observed adaptations of plants and
animals that inhabited many diverse
environments
• Main focus of geographic distribution of
species = Galápagos Islands near the
equator west of South America
The Galapagos Islands
• Small group of
islands 1000 km
west of South
America
• Very different
climates
• Animals on islands
unique
England
EUROPE
NORTH
AMERICA
PACIFIC
OCEAN
ATLANTIC
OCEAN
AFRICA
Galápagos
Islands
HMS Beagle in port
Equator
SOUTH
AMERICA
Darwin in 1840,
after his return
AUSTRALIA
Cape of
Good Hope
Cape Horn
Tierra del Fuego
Darwin returned 5
years later in
1836
Tasmania
New
Zealand
Darwin’s Focus on Adaptation
• Adaptation= a change in structure or
habits, often hereditary, to improve
survival and reproduction in environment
– Adaptation to environment and the origin of
new species  are closely related processes
• EXAMPLE
–Finches on the islands resembled a
mainland finch
–Finches had different types of beaks
adapted to their type of food gathering
LE 22-6
Cactus eater. The long,
sharp beak of the
cactus ground finch
(Geospiza scandens)
helps it tear and eat
cactus flowers and
pulp.
Seed eater. The large
ground finch (Geospiza
magnirostris) has a large
beak adapted for cracking
seeds that fall from plants
to the ground.
Insect eater. The green warbler finch
(Certhidea olivacea) used its narrow,
pointed beak to grasp insects.
Darwin’s Overall Observations
• Left unchecked, the # of
organisms of each species
will increase
• In nature, populations
tend to remain stable in
size
• Environmental resources
are limited
More of Darwin’s Observations
• Individuals of a
population vary in
characteristics with
no 2 individuals
being exactly alike.
• Much of this
variation between
individuals is
inheritable.
Darwin’s Overall Conclusions
• Production of more
individuals than can be
supported by the
environment leads to a
struggle for existence
among individuals
• Only a fraction of
offspring survive each
generation
• Survival of the Fittest
Darwin’s Conclusion
• Individuals who inherit
characteristics (adaptations) that
are most fit (suitable/favorable)
for their environment are
likely to leave more offspring
than less fit individuals
•Called FITNESS
•High survival = more offspring =
more fit
Darwin’s Conclusion
• Natural Selection
–gradual, nonrandom process by which traits
become more/less common in a population
–Acts on PHENOTYPES (adaptations), which
influences GENOTYPES
–only organisms best adapted to
environment tend to survive and transmit
genetic traits to future generations while
those less adapted tend to be eliminated
–Key mechanism to evolution
http://www.pbs.org/wgbh/evolution/educators/teac
hstuds/svideos.html
•Video #4: How Does Evolution Really Work?
• 1844
• Darwin wrote an essay on natural
selection but did not publish it
• 1858
• Alfred Russell Wallace developed
a similar theory of natural selection to
Darwin’s (organisms evolve from
common ancestors)
• Darwin quickly finished The Origin of
Species and published it the next year
Darwin’s Descent with Modification
• descent with
modification
• refers to idea that
all organisms are
related through
descent from
common ancestor
that lived in the
remote past
• the history of life is
like a tree
Darwin’s
st
1
Idea: Evolution
• What is evolution?
– All accumulated changes across successive
generations in inherited characteristics of populations
– A change over time in the genetic combination in a
population  give rise to diversity
• Darwins definition = Descent with
modification
Darwin’s 2nd Idea:
Natural Selection
•If an environment changes over time, natural
selection may result in adaptation to these new
conditions  new species can also evolve
Natural Selection vs.
Artificial Selection
• Recall Natural selection
– http://bcs.whfreeman.com/thelifewire/content/chp23/2
302001.html
• In artificial selection,
• humans modify other species over many
generations by selecting and breeding
individuals with desired traits
What is a “hypothesis” is
science?
• An educated prediction based on
observation
• IT MUST BE TESTABLE!!
• Usually supported or rejected through
experimentation or more observation
–A hypothesis can be disproven but it can
NOTbe proven true.
What is a “theory” is
science?
• Scientific definition of theory is different
from everyday meaning
– non-scientific context of “theory” implies that
something is unproven or speculative
• Scientific definition refers to a comprehensive
explanation of some aspect of nature that is
supported by a vast (A LOT)
body of evidence (data).
What is a “theory” is science?
• summarizes a hypothesis(es) that have been
supported with repeated testing
• If enough evidence accumulates
to support a hypothesis, it moves to the next
step—known as a theory—in the scientific
method and becomes accepted as a valid
explanation of a phenomenon
• a theory is an explanation or
model based on observation
– theories can be proven or rejected, just like hypotheses.
What is the difference between the
scientific method and a “theory” is
science?
• In the scientific method, there is a clear
distinction between facts, which can be
observed and/or measured
• In a theory, scientists create explanations
and interpretations of the facts which have
been observed and/or measured
REPEATEDLY using the scientific method
– A good theory is that it formed from a number of
hypotheses that can be tested independently.
What is a “law” is science?
• A theory is an explanation of an
observations
• A law is a description of observations
– no exceptions have been found to a law
– laws explain things, but they do not describe them.
• One way to tell a law and a theory apart is to ask if the
description gives you a means to explain 'why'.
– Many laws are mathematical equations.
– EXAMPLE:
• Kepler's Laws of Planetary Motion, for example, describe the
motions of planets but do not provide an explanation for
their movements.
What is a “belief”?
• Definition
–trust, faith or confidence in someone
or something
• faith almost always implies certitude
even where there is no evidence or
proof
Often not based on REPEATED collected data!
Is Evolution JUST a
THEORY??? Is it SCIENCE
based?
• http://www.pbs.org/wgbh/evolution/educa
tors/teachstuds/svideos.html
• Video #1: Isn’t Evolution Just a Theory?
1. Homology
• a similarities in characteristic traits resulting from
common ancestry
2. Anatomical Homologies
• anatomical resemblances that represent
variations on a structural theme present in a
common ancestor
• Called HOMOLOGOUS STRUCTURES
• Same development, different
function
LE 22-14
Human
Cat
Whale
Bat
3. Vestigial
organs
• remains of structures
once important in
organism’s ancestors
–Example: tailbones
in humans,
appendix, wings on
ostrich, wisdom
teeth in humans
4. Comparative Embryology
5. Molecular Homologies
• Similar genes (DNA), RNA or
amino acid sequences
–Example
• genes shared among organisms
inherited from a common ancestor
• Ex #1: Homeobox is a DNA
sequence in genes that regular
development in plants, animals and fungi
• http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.
html
LE 22-16
Species
% of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
Human
100%
95%
Rhesus monkey
87%
Mouse
69%
Chicken
54%
Frog
Lamprey
14%
Ex #2:
Amino
Acid/
Protein
sequence
6. Biogeography
• the geographic distribution of species
Sugar
Glider
Marsupial
•Some similar mammals that
have adapted to similar
environments have evolved
independently from different
ancestors
Flying
Squirrel
Eutherian
(placental)
7. Genetic Changes over
time
• Bacteria becomes resistant
to antibiotics
7. Fossil Records
• Paleontologists have discovered
fossils of many transitional forms
• Shows variety on organism across
time
Key Concepts
What is the raw material necessary for
the mechanism of Natural Selection?
• Heritable variations
What is the smallest unit of evolution?
• Populations (NOT individuals)
• Darwin incorporated Lyell’s gradualism into
biological evolution combined with Malthus’
observations regarding populations
Some Cool Evolution Videos…
• Poison Newts
– http://www.pbs.org/wgbh/evolution/library/01/3/l_013_07.ht
ml
• Camouflage “Leaves”
– http://www.pbs.org/wgbh/evolution/library/01/1/l_011_03.ht
ml
• Evolution of the Eye
– http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.ht
ml
• Why Does Evolution Matter Now? (Video #6)
– http://www.pbs.org/wgbh/evolution/educators/teachstuds/svi
deos.html