Download Ch. 15, Darwin`s Theory of Evolution

Definitions to Know
• Scientific Theory = a wellsupported, testable explanation
of phenomena that have
occurred in the natural world.
• Evolution = change over time,
the process by which modern
organisms descended from
ancient organisms
Charles Darwin (1809-1882)
• British naturalist famous for his theories of
evolution and natural selection.
• Like several scientists before him, Darwin believed
all the life on earth evolved (developed gradually)
over millions of years from a few common
ancestors.
• In 1831, Darwin took a trip around the world on the
ship, the M.S. Beagle, where he collected
evidence that led him to propose his famous
Theory of Evolution.
Charles Darwin
Darwin’s Voyage on M.S. Beagle
Starting point:
1831, England
Ending point:
1836, England
Did you know there are no rabbits in Australia?
No kangaroos in England? No monkeys in
North America? No elephants in Alaska?
Darwin’s observations showed him there were
patterns to the diversity of life on Earth. Organisms
are adapted to the environment where they live.
Fossils
• Darwin didn’t just observe and collect living animals,
he also collected fossils.
• Fossils = preserved remains of ancient organisms
• This led to questions like….
– “Where did all these organisms go?” “Why aren’t
they still here?” “Why do they resemble organisms
we have living today?”
Glyptodon = dead
Armadillo=
alive
The Galapagos Islands
• The most important, influential
stop on Darwin’s trip was the
Galapagos Islands
• The islands had different
climates, and therefore, had
different varieties of animals and
plants
1.
Giant Tortoises
3. Finches
2. Iguanas
Galapagos Turtles
Pinta
Tower
Marchena
Pinta Island
Intermediate shell Fernandina
Hood Island
James
Saddle-backed shell
Santa Cruz
Isabela
Santa Fe
Floreana
Isabela Island
Dome-shaped shell
Hood
The shape of each turtle’s shell is
different and the different shapes
depend on the turtle’s habitat.
Darwin’s Finches
• Darwin also collected finches, birds, matching
their beak and body shapes with different
islands- just like the tortoises.
• Beak shapes in the finches indicated their
type of diet, what they ate, and this told him
where they lived
Tree Finch
Ground finch
Darwin’s
Finches
FYI, each beak is
designed for a
different purpose.
Box 12
Leaves
Seeds and Fruit
Seeds
Insects
Grubs
Tool using
What took him so long? 25 years
later….
• In 1858, Alfred Wallace sent Darwin an essay with
the same ideas about evolution!
• They presented their work together at a conference,
but….
• This pushed Darwin to publish
his work, before Wallace
• The Origin of the Species
– Proposed a mechanism for evolution, called
Natural Selection
– Presented evidence that evolution has
been happening for millions of years
Artificial Selection and Natural
Selection
• Variation exists in nature and animal and plant breeders use this
through artificial selection
– A farmer may like a see a plant with bigger tomato and use
the seeds of that plant for next year’s crop
– Or he may breed the two best milk cows to get a cow who is
an even better producer of milk
• Darwin’s greatest contribution was his concept of natural
selection
• In the struggle for survival, the most fit- the fastest prey, the
strongest predator, the one with the sharpest claws, wins the
game of survival. Survival of the fittest.
• Fitness = the ability to survive and reproduce in a specific
environment
Adaptation = any inherited
characteristic that increases
an organisms chance of
survival
Proof for Evolution
Beaver
Muskrat
Beaver and
Muskrat
Coypu
• Fossil record = Darwin argued that
the fossil record provided evidence
that living things have been evolving
for millions of years
Capybara
Coypu and
Capybara
• Geographic Distribution of living
species:
Descent with modification, says that
similar species in similar
environments but in different
locations, were products of different
evolution paths
• They developed similar
characteristics because of their
environment.
Homologous Body Structures
Homolgous structures all
develop from the same
embryo tissues but have
different functions in the
adult organism.
• What does Homo mean?
– Homo = same, similar
• Remember these?
– Homozygous- same allele for a trait, tt, TT
– Homologous chromosomes- same chromosome,
one from mom one from dad
Turtle
Alligator
Ancient lobe-finned fish
Bird
Mammal
Vestigial organs
• Why do we need our appendix?
• It’s useless now, but it may have served some
function in our past
• Vestigial organs = organ with little or no
function, left over from the past, ex. appendix
If you can live without
it, with no medical
help, then it’s useless!
Ch. 16, Evolution of Populations
• Why are we all so different?
• Variation in populations is the raw
material for evolution
• 2 main sources of variation:
– Mutations = any change in a
sequence of DNA, some are
harmful, some are beneficial and
some don’t have any effect at all
– Gene shuffling = mixing of genes
due to random sexual mating
• 23 pairs of chromosomes can
produce 8.4 million different
combinations of genes
• Crossing over during Meiosis
Variation and Gene Pools
• Genetic variation is studied in POPULATIONS,
not individuals
• Members of a population share a Gene Pool
• Gene pool = consists of all genes, including all the
different alleles that are present in a population
– Why?
– They descended from a common ancestor
• Relative frequency of an allele = number of
times an allele occurs in a gene pool
• So, evolution is any change in the relative
frequency of alleles in a population
Natural Selection and
Speciation
• Natural Selection= (Dr. Malone’s definition) when
individuals who have what it takes survive and
reproduce best; survival of the fittest, it’s a dog eat
dog, you got to step on someone else to get where
you want to go, world
• Founder Effect = when a population shrinks down to
only a few members, then rebounds so all of the
future members have the “founder’s” genes
• Speciation = when natural selection and
other random effects lead to the creation
of a new species
– Reproductive Isolation = populations become
reproductively isolated from each other, so it
leads to evolution of a new species
Speciation
• Behavioral Isolation = when two populations can
interbreed, but their different behaviors, or
reproductive strategies, just don’t turn each other
on, get it?
• Geographic Isolation = two populations are
separated by geographic barriers, like mountains or
oceans and they can’t interbreed
•Temporal Isolation = two populations are
separated by different reproductive
It’s tootimes
Move mountain!
Move mountain!
far to fly!