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EVOLUTION
• Jean Baptiste de Lamarck (1809) –
He developed a theory of evolution. He related
fossils to living animals based on similar
appearance.
• He was the first to state
that organisms change
over time, and new types
are modified descendents
of older types.
Lamarck stated that acquired traits could
be passed to offspring
(The Theory of Acquired Inheritance)
"All which has been acquired, laid down, or
changed in the organization of individuals
in the course of their life is conserved by
generation and transmitted to the new
individuals which proceed from those
which have undergone those changes.”
This means that according to
Lamarck, acquired traits could
be inherited by the next
generation.
The Giraffe example: The giraffe’s long
neck could be the result of generations of
giraffes stretching to reach leaves in high
branches over their lifetime. Parents slightly
stretch their necks and therefore have offspring
that inherit this modification acquired during their
parents’ life.
If a giraffe stretched its neck for leaves,
for example, a "nervous fluid" would flow
into its neck and make it longer. Its
offspring would inherit the longer neck,
and continued stretching would make it
longer still over several generations.
A new look at giraffe
neck adaptation
The Long-Legged Bird Example:
The long legs of wading birds arose when their
ancestors responded to a need to feed on fish.
As they waded in deeper water, they stretched
their legs to try and keep their bodies dry. This
trait would be passed to the next generation.
Example of webbed feet:
"The development of organs and their
force of action are constantly in ratio to the
employment of these organs."
Lamarck stated that there could be
changes in acquired traits through use
or disuse.
• Lamarck also proposed that organisms
were driven from simple to increasingly
more complex forms.
(Darwin argued that
increased complexity was the result of adaptation to
local environments from one generation to the next.)
• He did not think species
ever went extinct, they
just changed into
new forms.
Charles Darwin (1809 – 1882) After
college, a young Charles Darwin (22 yrs
old), in 1831, set sail aboard the HMS
Beagle as the ship’s naturalist. (The ship
was chartered for a five-year mapping
mission.)
Darwin 1840
Darwin was required to collect specimens and
carefully record his observations. Darwin was
often left at various sea ports for months at a
time, which enabled him to collect many fossils
and observe thousands of specimens.
Darwin’s Voyage
Darwin read Principles
of Geology by Charles
Lyell, who stated that
the geological
structure of the Earth
resulted from cycles
of observable
processes that
operate continuously
through time.
Darwin also read about
James Hutton’s work:
In 1795, Hutton, a
geologist,
published a theory
that the Earth is
shaped by
geologic forces that
take place over
Extremely long periods
of time. He estimated
the Earth to
be millions of years old.
During Darwin’s journey, he witnessed
a volcanic eruption, & an earthquake
that lifted a portion of shoreline and
noted that animal life in the water was
displaced.
Darwin also observed fossil shells of
marine organism in rock beds about
4,300 meters (14,100 ft) above sea level.
Darwin concluded that if the Earth
could change over time, then life could
change as well. He also assumed that
it would have taken many, many years.
The Galapagos Islands are a group of small
islands near the equator, about 600 miles off the
coast of South America. The observations and
specimens Darwin collected were especially
important to developing his theory.
white areas over
islands are clouds
Darwin’s Finches: Darwin collected many
specimens of finches from the
Galapagos Islands and found that he had
several similar but separate species.
Darwin had collected 13 different species, each
with a different bill specialized for a particular
food source.
• Since there were so many similarities,
he believed this implied that the finches
shared a common ancestor.
• He assumed the differences in the bills
of offspring were adaptations to
different environments.
• He also assumed that over many
millions of years, many large
differences could accumulate
between species.
Darwin’s tortoises: Darwin found that the
shapes of tortoise shells corresponded to
different habitats.
• The hood Island tortoise has a long neck and a shell that
is curved and open around the neck and legs, allowing
the tortoise to reach sparse vegetation.
• The Isabela Island tortoise has a dome-shaped shell & a
shorter neck. Vegetation on this Island is more abundant
and closer to the ground.
• Pinta Island tortoises have
an intermediate shell
between these two forms.
Another important idea that aided Darwin’s
conclusions about the change in organisms
was proposed by Thomas Malthus in 1798.
He stated that the human population could
double & redouble, except for
the presence of war, disease,
or limited food supplies.
Darwin’s conclusions:
• 1) Darwin reasoned that all organisms have
environmental limits to their growth which
decrease their rate of reproduction or increase
their rate of death.
• 2) Organisms compete for limited resources.
• 3) Certain traits are beneficial to an organism’s
survival, as well as greater reproductive
success. If the trait increases the reproductive
success, & is inherited, it is passed to many
offspring.
• 4) Organisms adapt to their environment as
their proportion of genes for favorable traits
increases.
• 5) The resulting change in genetic makeup is
evolution. The genetic contribution to the next
generation termed fitness.
• 6) An individual with a high fitness is welladapted to its environment and reproduces
more successfully than an individual with
low fitness.
Natural Selection -“Survival of the fittest.”
Individuals best suited
to their environment
survive and reproduce
the most successfully,
and pass their favorable
traits to offspring. While
those with more poorly
-suited traits die, or
leave fewer offspring.
• Species change over long periods of time.
Natural selection causes the changes in
species. New species arise, while others
Species alive today descended, with
modifications from species that lived in the
past. All organisms on Earth are united
in a single tree of life by common descent.
Darwin and Lamarck
Darwin did not accept an arrow of complexity driving
through the history of life. He argued that complexity
evolved simply as a result of life adapting to its local
conditions from one generation to the next.
Darwin also argued that species could go extinct rather
than change into new forms.
But Darwin also relied on much the same evidence for
evolution that Lamarck did (such as vestigial structures
and artificial selection through breeding).
Artificial Selection and Natural Selection:
Breeding organisms with specific traits
in order to produce offspring with identical
traits is called “Artificial selection.”
Darwin used the term
“Natural selection” to
describe nature’s forces
Selecting which traits
are favorable and which
organisms are better fit to survive.
Natural Selection, the key evolutionary
mechanism Darwin identified, is really
four key processes
• genetic variation (difference in genomes among
organisms in a given population)
• overproduction of offspring
• struggle for existence
(competition for food, mating resources etc.)
• differential survival and reproduction
(higher fitness, & better adaptation leads to more
offspring).
Natural Selection (Modern Biology pg 300)
Natural Selection and peppered moths:
As pollution darkens the trees which moth
is favored to survive?
Darwin was asked by the naturalist Alfred Wallace, in
1856 (22 years after Darwin returned to England on
the Beagle) to review his paper on “Natural Selection”
as a mechanism for Evolution.
Darwin decided to publish his own work on evolution.
Both papers were presented to the Linnaean Society
of London in 1858.
Darwin wrote his now famous
book, On the Origin of
Species by Means of
Natural Selection, more
commonly
known as
The Origin
of Species.
What causes changes in a population of
organisms?
Darwin did not know how heredity worked.
Therefore he did not know the source of the
variation that was
central to his theory,
or how these traits
were passed to offspring.
Two main sources of genetic variation:
• 1) Mutations - Mutations do not always affect
an organism’s phenotype, but some may enhance
an organism’s ability to survive and reproduce.
• 2) Sexual reproduction - The Genetic
“shuffling” that results from sexual reproduction
causes variations in a population.
Genes mutate from one form to another. New alleles are
introduced into the population, and allele frequencies change.
-------This can lead to evolution.
Populations, Not Individuals Evolve
Within an organisms lifetime, it cannot evolve a
new phenotype by natural selection.
Natural selection
acts on
the range
of phenotypes
in a population.
All the genes of a population
are referred to the gene pool.
The percentage of any allele
in that pool is the allele
frequency.
If there are no changes in
the allele frequencies, then
there is genetic equilibrium
evolution does not occur.
• Environmental factors can affect the
allele frequencies and cause evolution.
• Mutations can be causes by chemicals
etc. and bring about useful variations and
new genes in the gene pool.
• The gene pool can be affected by
movement of individuals in and out of
the population.
The change in alleles has been
naturally selected.