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The Theory of Evolution
Charles Darwin
• From England.
• Med school drop out, Clergy
drop out.
• Parents sent him on a boat to
get rid of him.
• Came up with the idea of
NATURAL SELECTION.
Natural Selection
• Concept that deals with and
explains how EVOLUTION
works.
• Evolution = changes in
populations over time.
Fossil Evidence
• Suggests that species have
changed over time.
• Geologic evidence suggests that
simple life forms appeared first
followed by more complex.
Darwin’s Voyage
• Age 21, 1831
• Job: ships Naturalist on the
HMS beagle.
• Spent 5 years collecting &
making observations.
Galapagos Islands
• Studied finches (small birds),
and other animals. All these
animals were unique to the
island but similar to other kinds
of animals.
• Spent the next 22 years
collecting, studying, reading
and conducting experiments.
• Then he wrote his book called
“ON the Origin of Species by
Natural Selection” in 1859.
Meanwhile back at the ranch...
• Thomas Malthus proposed that
populations grow faster than
their food supply.
• He knew that many species
produced many offspring but
never overran the Earth.
• Proposed that there was
competition for food, space,
mates, shelter, etc.
• It was a struggle to survive.
• Which individuals survive?
Darwin had an Answer
• By breeding pigeons Darwin
noticed he could breed birds
with favorable traits.
• Darwin proposes Natural
Selection.
Natural Selection
• Darwin reasoned that organisms
survive better if they have
certain traits that make them
more fit to compete.
• Organisms without these traits
struggled more and were less
likely to survive.
• As a result the parents with
favorable traits produced
offspring with favorable traits,
so they were more likely to
survive.
• Parents without favorable traits
produced offspring without
favorable traits who were less
likely to survive. Until the traits
become extinct.
Today’s evidence
• Volumes of scientific data have
been gathered in support of
Darwin’s theory.
• Most scientist accept the theory
of evolution as proposed by
Darwin.
However...
• Since the human life span is so
short and evolution take
millions of years to occur, direct
observation is hard to come by.
However...
• Many studies of organisms with
very short life spans have
shown conclusive evidence that
evolution does occur.
Evidence for Evolution
Structural Adaptations
• Structural adaptations over
time.
• Teeth, claws, blindness, thorns,
quills.
• Mimicry - structural adaptation
that enables one species to
resemble another species .
• Blow snake rattle its tail like a
rattle snake.
• Camouflage
• enables some species to blend
into their environment, making
it harder for predators to hunt
them.
Physiological
Adaptations
• Bacteria in Fleming’s day
(1929) were not resistant to
antibiotics. Today many are.
• Weeds, Insects.
Fossils
• Fossils show a sequence of life
from simple to complex.
• Some fossils look like
organisms of today.
Anatomy
• Homologous structures:
• The bones of a whale forelimb,
crocodile forelimb and a bird
wing all have the same bones.
• Analogous structures
• Insect wings and bird winds.
Totally different but serve the
same purpose.
• Different ancestors similar way
of life, evolved independently
of each other
• Vestigial structures
• A body structure that has no
function in a present day
organism but was probably
useful to an ancestor.
• Mole rats eyes, they are blind
but still have eyes.
• Humans tail bone, & appendix.
Embryology
• In the earliest stage of growth
many organisms have gill slits,
but loose them as they mature.
• Fish, reptile's, birds, and
mammals.
Biochemistry
• Comparisons of DNA and RNA
of different species produce
evidence for evolution.
Homework
• Page 411 #1-6
• Worksheet on biochemistry.
• Do Natural Selection Lab.
Mechanisms of Evolution
• Gene - codes for a trait
• Genotype - The actual type of
genes you have. (2, 1 from mom, 1
from dad)
• Phenotype - Outward expression
of your genes.
• Allele - Different manifestation of
the same gene.
Populations Genetics
and Evolution
• Darwin developed his theory
before genes were discovered.
• Since then the field of
population genetics has been
created to help study evolution.
• Organisms that have genes
(trait) that produce a phenotype
(visible trait) that is poorly
adapted to the environment,
may hamper the organisms
ability to survive.
• Remember the Natural selection
lab?
• Beads that were easily seen
were easily hunted, some to
extinction.
• Organisms cannot evolve a new
phenotype within their lifetime.
• If your phenotype is favorable
you have the advantage over
others who do not.
• Within a population however,
there are many different
phenotypes (remember the
beads, 100 beads, 10 of each
color)
• Evolution occurs as a
population’s genes and their
frequencies change over time.
• All the alleles in a population’s
genes is know as the gene pool.
The larger the gene pool the
greater variation you have
within the population.
• The percentage of any specific
allele in the gene pool is called
the allelic frequency.
• Scientists can calculate the
frequency of an allele the same
way a batting average is
calculated.
• When the frequency of alleles
remains unchanged over several
generations it is said that
genetic equilibrium has
occurred.
• Scientist look at different
populations and calculate the
allelic frequency, to determine
if the population is evolving or
not.
Causes for changes in
genetic equilibrium
• Mutations: random changes in
the DNA caused by radiation,
chemicals, or chance.
• Most mutations are lethal, some
however are useful, thus
becoming part of the
populations gene pool by
natural selection.
Genetic Drift
• The alteration of allelic
frequencies by chance event.
• Populations becoming isolated.
• Human populations isolating
themselves, religion, etc.
Gene Flow
• The transportation of genes
from one population to another.
• Genes are lost form one
population and added to
another.
Natural Selection
• Still considered the number one
cause of evolution.
Natural selection and
variations
• Variations of a single trait
sometimes increase or decrease
an organisms chances for
survival.
• Stabilizing, directional,
disruptive.
Stabilizing
• Natural selection that favors
average individuals in a
population.
• Average sized spiders survive.
• Small spiders have a hard time
finding food.
• Large spiders get eaten by
predators.
Directional selection
• Natural selection favors one
extreme variation.
• Deer with large antlers usually
get shot by hunters
• Deer with small antlers survive
better because they are hunted
less.
or
• Forest is infected with insects
that bore deep into a trees bark.
• Woodpeckers with longer beaks
could feed on the insect.
• Woodpeckers with shorter
beaks starve and die.
Disruptive selection
• Individuals with either extreme
of a trait’s variation are selected
for.
• Limpets - sea shell colors range
from white, to tan, to dark
brown.
• White Limpets on light colored
rocks survive.
• Dark brown Limpets on dark
rocks survive
• All the tan ones get eaten by
birds.
Speciation
• Species - a group of organisms
that look alike and can
interbreed to produce fertile
offspring.
• Speciation occurs when
members of similar populations
no longer interbreed.
Causes of speciation
• Physical barriers - break a
single large population into
smaller separate ones.
–Volcanoes, canyons,
continental drift…
• This causes geographic
isolation.
• This decreases the size of the
gene pool in the population thus
reducing each populations
chances to remain like one
another.
Reproductive isolation
• Occurs when formerly
interbreeding organisms can no
longer mate.
• Usually due to a change in the
genetic material that causes the
populations to become so
different that fertilization
cannot occur.
• Sometimes reproductive
isolation is caused by behavior.
• One kind of tree frog.
• Some mate at night, some mate
during the day.
• Eventually they become two
separate groups.
Patterns of Evolution
• Hawaiian honeycreepers found
only in Hawaii.
• 14 different kinds.
• Very similar body size and
structure.
• Colors and beaks differ sharply
Scientists hypothesize
• Honeycreepers evolved from a
single species.
• Suggests adaptive radiation
Adaptive radiation
• When an ancestral species
evolves into an array of species
to fit the number of diverse
habitats.
• adaptive radiation is a type of
Divergent evolution.
• Meaning one becomes many.
• Occurs when populations
adapting to different
environmental conditions
change to the point they become
a new species.
Convergent evolution
• A pattern of evolution in which
distantly related organisms
evolve similar traits.
• Occurs when unrelated species
occupy similar habitats in
different parts of the world.
• Euphorbs in African deserts
• Cactus in North and South
American deserts.
• Homework SA 15.2 page 421
#1-5.
• Vocabulary page 425.
• CA 15 page 425 # 1-25.