Download 6.1_EVOLUTION_DARWIN VS LAMARCK

Darwin &
Evolution by
Natural Selection
Cactus
eater
Insect eaters
Seed eaters
Bud eater
2006-2007
Darwin & Lamarck
Written by Jennifer Folsom
Background Information Natural Selection is a scientific theory that has been supported by
tremendous amounts of scientific evidence. In this lesson, students will be exposed to Natural
Selection and an earlier alternate theory—Acquired Inheritance. Both of these theories are
founded on the belief that animal species change over time and that offspring inherit traits from
their parents. The two theories differ on how animals change and what traits offspring inherit
from their parents. The theory of Acquired Inheritance was introduced by Jean Baptiste Lamarck.
It was based on his belief that individual organisms made changes in themselves and passed those
changes on to their offspring. In his theory, individual organisms had the ability to change their
physical characteristics. Giraffes that needed longer necks, or elephants that needed longer trunks
would use them more and they would extend them through use. Lamarck not only believed that
animals could make these changes, but also that they could pass them on to their offspring. For
example, when mama giraffe stretched her neck a little to reach more food, it would stay
stretched, and her new baby would have that long neck too. Charles Darwin introduced Natural
Selection to the scientific community. He said that organisms could neither willfully change
themselves nor pass those changes on to their offspring. He said that individuals survived (or
didn’t) based on the specific traits they possessed. His well-known saying “survival of the fittest”
meant that out of the entire population of one type of organisms, only the fittest will survive in an
environment with limited resources. Those with the best adaptations for survival stayed alive and
were most likely to reproduce. When they reproduce, they passed on their beneficial traits to their
offspring. Eventually, the population had a higher percentage of individuals with those more “fit”
traits. If the environment changed again in some way, the process happened again. As long as
environments continue to change, so will makeup of populations of organisms. Natural Selection
is the driver behind evolution.
Incorrect Theories of Evolution:
Lamarck
• Lamarck proposed an incorrect mechanism
for how organisms evolve.
– Believed organisms could pass on aquired traits
to offspring
– Simple life forms continually came into
existence from dead matter
– Continually become more complex
– More "perfect" -- as they transformed
into new species.
• He correctly pointed out that change in
species is linked to an organism’s
environment.
Charles Darwin
• Proposed a way how
evolution works
– How did creatures change
over time?
– by natural selection
• Collected a lot of
evidence to support his
ideas
– 1809-1882
– British naturalist
– -Wrote the Origin of
Species
Voyage of the HMS Beagle
• Invited to travel around the world
– 1831-1836 (22 years old!)
– makes many observations of nature
• main mission of the Beagle was to chart
South American coastline
Robert Fitzroy
Voyage of the HMS Beagle
• Stopped in Galapagos Islands
– 500 miles off coast of Ecuador
Galapagos
Recently formed volcanic islands.
Most of animals on the
Galápagos live nowhere else in
world, but they look like species
living on South American
mainland.
800 km west of Ecuador
Darwin’s Observations
• Animals on the coast of
S. America:
– Resembled those on the
nearby islands
– Evolved differences
Or
– Descended w/
modification after
separating from a
common ancestor.
Darwin found…many unique
species
Many of Darwin’s observations made him
wonder… Why?
Darwin asked:
Why were these creatures found only on the
Galapagos Islands?
Darwin found…clues in the
fossils
Darwin found:
Evidence that creatures
have changed over time
present day Armadillos
Darwin asked:
ancient Armadillo
Why should extinct
armadillos & modern
armadillos be found on
same continent?
Darwin found… more
fossils
Darwin found:
Evidence that creatures
have changed over time
present day Sloth
(extinct) Giant ground sloth
Darwin asked:
Why should extinct
sloths & modern
sloths be found on
the same continent?
Darwin found:
Different shells on tortoises on different islands
Darwin asked:
Is there a relationship
between the environment &
what an animal
looks like?
But Darwin found… a lot of finches
Darwin was amazed to
find out:
All 14 species of birds
were finches…
But there is only one
species of finch on the
mainland!
Large
Small
ground finch
Finch?ground
Sparrow?
Finch?
Sparrow?
QuickTime™ and a
Photo - JPEG decompressor
finch
are needed to see this picture.
Darwin asked:
If the Galapagos finches
came from the mainland,
why are they so different
now?
Warbler
finch
Woodpecker?
Woodpecker?
Tree finch
Warbler?
Warbler?
The finches cinched it!
Darwin found:
The differences between
species of finches were
associated with the
different food they ate.
different beaks are inherited
variations
 serve as adaptations
that
help birds
Darwin
said:compete for
food
Ahaaaa!
 these birds survive &
Aground
flock
Large
Big seed
eater of South
Small
ground
seed
eater
finch
Finch?
Sparrow?
reproduce
finch American finches were
 pass on the genes for those
stranded on the
more fit beaks
Galapagos…
 over time nature selected for
different species with
different beaks

QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Insect
Warbler
eater
finch
Woodpecker?
Tree finch
Leaf
& bud eater
Warbler?
Relationship between species (beaks) & food
Darwin’s finches
• Darwin’s conclusions
– variations in beaks
• differences in beaks in the original flock
• adaptations to foods available on islands
– natural selection for most fit
• over many generations, the finches were selected for
specific beaks & behaviors
– offspring inherit successful traits
• accumulation of winning traits:
both beaks & behaviors
– separate into different species
From 1 species to 14 species…
Warbler finch
Cactus finch
Woodpecker finch
Sharp-beaked finch
Small
insectivorous
tree finch
Large
insectivorous
tree finch
Small
ground
finch
Cactus
eater
Insect eaters
Medium
ground
finch
Seed eaters
Vegetarian
tree finch
variation
Bud eater
natural selection for best
survival & reproduction
Large
ground
finch
Growth of Populations
• Darwin was influenced by Thomas Malthus
• He wrote:
Populations grow as much as the environment allows.
Evolution by Natural Selection
• The process of:
“Survival of the Fittest”
• Organisms that adapt
to their environment
survive while those
that do not adapt
disappear
• N.S. leads to
adaptations in a
population.
ADAPTATIONS LEAD TO
FITNESS
Living things that are well adapted to their environment survive
and reproduce. Those that are not well adapted don’t survive and
reproduce.
An adaptation is any characteristic that increases fitness, which
is defined as the ability to survive and reproduce.
 YOU CANNOT AQUIRE AN ADAPTATION, MUST BE AN
INHERITED TRAIT.
Label Paper:
1. Genetic Variation
a.
b.
Natural
Selection Video
http://www.pbs.org/wgbh/evol
ution/library/11/2/e_s_4.html
6 min 39 sec
2. Overproduction of
Offspring
a.
b.
3. Struggle for Existence
a.
b.
4. Differential Survival &
Reproduction
a.
b.
SUMMARY: Individuals best suited to their environment
survive and reproduce most successfully. The characteristic
that make them best suited to their environment are passed on
to offspring.
Individuals whose characteristics are not as well suited to
their environment die or leave fewer offspring.
Species change over time. This is natural selection.
Over long periods of time, natural
selection causes changes in the
characteristics of a species, such
as in shape and form. New
species arise, and other species
disappear.
Species alive today have descended with modifications form
species that lived in the past.
African wild
Jackal
Fox
dog
Thousands to
millions of
years
of natural
selection
•These five canine
species evolved from a
common ancestor
through natural selection
Fox
Coyote
Wolf
Ancestral canine
Darwin’s Ideas Updated
1) Change Within Populations
• N.S. causes the frequency of certain alleles in a population
to change over time.
2) Species Formation
• Under certain conditions, change within a species due to
reproductive isolation can lead to new species.
3) The Tempo of Evolution
• Gradualism is a process of evolution in which speciation
occurs gradually
• Punctuated Equilibrium is a process in which speciation
occurs rapidly between periods of little or no change.
Examples of Evolution-Natural Selection at Work
1) Factors in Natural Selection
• Organisms w/traits helping them survive—
reproduce & pass genes.
2) Evolution of Antibiotic Resistance
• Experiments show that evolution through N.S. has
occurred within populations of antibiotic-resistant
bacteria
– Tuberculosis bacteria
3) Evolution in Darwin’s Finches
• Experiments show that evolution through N.S. has
occurred in beak size in Darwin’s Finches.
Formation of New Species
1) Speciation
• Speciation begins as a population adapts to its
environment.
2) Forming Subspecies
• Populations of the same species that differ
genetically b/c of adaptations to different living
conditions are called: subspecies.
• Newly formed subspecies are on the road towards
speciation.
3) Maintaining New Species
• Reproductive isolation through barriers keeps
species from breeding with one another.
Speciation
• Geographic isolation of populations
• Can lead to
• Reproductive isolation of population
• Can lead to
•
•
New Species
(unable to breed when together)
Geographic Isolation
• Members of
a population
may
become
isolated
from one
another by
geographic
boundaries
like
mountains,
rivers or
even oceans
Reproductive Isolation
Convergent Evolution
Divergent Evolution
(Adaptive Radiation)
Dichotomous Keys
• Tool used when new species is found
• Used to categorize different species based on
physical characteristics
• Classification is a way of separating a
large group of closely related organisms
into smaller subgroups.
• A Dichotomous Key is a listing of
characteristics, such as structure and
behavior, organized in such a way that an
organism can be identified or classified.