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Evolution
Evolution
Change over time
 Process by which modern
organisms have descended
from ancient organisms
Charles Darwin
Born in England 1809
 Set sail on H.M.S. Beagle in
1831 for voyage around the
world
 Made numerous observations and
collected evidence that led him to
propose the theory of evolution –
how life changes over time
Darwin’s Voyage
Darwin’s Observations
Observed a tremendous
amount of diversity in plants and
animals
 68 different beetle species in
one day in a Brazilian forest
 Plants and animals well suited
to whatever environment they
inhabited
Darwin’s Observations
Intrigued by which organisms
survived and produced offspring
Collected fossils that
resembled organisms that were
still alive
 Most influenced by Galapagos
Islands
Galapagos Islands
Very different
climates on each
island
 Paid particular
attention to giant
tortoises, marine
iguanas, and finches
 Organisms varied in
predictable ways
from one island to
another
 ie. Tortoise shells
Galapagos Islands
Darwin proposed that animals
living on different islands had once
been members of the same species
 Species would have evolved from
an original South American
ancestor species after becoming
isolated from one another
Galapagos Tortoises
Pinta Island
Intermediate shell
Hood Island
Saddle-backed shell
Isabela Island
Dome-shaped shell
Darwin’s Influences
• Society was not receptive to Darwin’s
“radical” ideas
• Certain scientists who preceded
Darwin helped to shape his views
Hutton’s Theory
• Hutton’s Theory of Geological
Change
• James Hutton (1795) a geologist
– Rocks, mountains, and valleys are
shaped by a variety of natural forces
–i.e. Rain, heat, & cold temperatures
– Geological processes operate extremely
slowly therefore Earth had to be much
older than a few thousand years old
Lyell’s Principles
• Lyell’s Principles of Geology
• Charles Lyell (1833) geologist
–The processes that changed Earth
in the past are the same processes
that operate in the present
–Scientists recognize that Earth is
many millions of years old
Movement of Earth’s Crust
Sea
level
Sea
level
Sedimentary
rocks form in
horizontal layers.
When part of Earth’s
crust is compressed,
a bend in a rock
forms, tilting the rock
layers.
As the surface
erodes due to water,
wind, waves, or
glaciers, the older
rock surface is
exposed.
New sediment is
then deposited
above the exposed
older rock surface.
Lamarck’s Theory of
Evolution
• Jean Baptiste Lamarck French
naturalist (1809)
• proposed that by selective use or
disuse of organs, organisms acquired
or lost certain traits during their
lifetime.
– These traits could be passed on to their
offspring.
– Led to changes in species
Tendency Toward
Perfection
• All organisms have a innate
tendency toward perfection
–Ancestors of birds acquired an urge
to fly,
–Birds kept trying to fly,
–Their wings increased in size,
–Birds are now suited to flying
Use and Disuse
• Organisms could alter the size or
shape of particular organs by
using their bodies in new ways
–Birds try to use front limbs to fly,
they grew wings
–If a winged animal did not use its
wings they would decrease in size
and disappear
Inheritance of Acquired
Traits
• Lamarck thought acquired
characteristics could be
inherited.
–If you spent your life lifting
weights to build muscles then
your children would inherit big
muscles, too.
Crab Claws
http://www.youtube.com/watch?v=ad4CAu2S-j8&feature=related
Evaluating Lamarck
• Lamarck’s theory of evolution is incorrect
because:
– He did not know how traits are inherited.
– Behavior has no effect on genetics
• He was the first:
– to develop a theory of evolution
– First to realize that groups of organisms
do adapt to their environment
Population Growth
• Thomas Malthus (1798) – English Economist
• Observed that babies were being born faster
than people were dying.
• Malthus reasoned that if the human population
continued to grow unchecked, sooner or later
there would be insufficient living space and food
for everyone.
– Proposed that war, famine, and disease limit
the growth of human populations.
Darwin Presents His Case
• Publication of On the Origin of Species
* Darwin’s discoveries went totally
against the scientific ideas of the
1800’s
* He did not publish his research until
he read Alfred Russel Wallace’s
essay, which summarized Darwin’s
thoughts on evolution.
* Published 25 years after his trip
Natural variation and
artificial selection
• Darwin’s critics believed that all
species were perfect and unchanging
• Natural variation: differences among
individuals of a species, found in all types
of organisms.
– Darwin proposed that much of the
variation in populations can be inherited,
or passed on to the next generation
Artificial Selection
• Darwin actually made some of his
greatest progress studying English
farmers and breeders
• Artificial selection: nature
provides variation among different
organisms, humans select and
breed for those variations that they
find useful.
Artificial Selection
Evolution by Natural
Selection
* The struggle for existence
* Competition for resources
* Food, water, shelter, mates,
etc.
“Survival of the Fittest”
• The better suited an organism is to its
environment, the better chance it has at
surviving
• The inherited characteristics that
increase an organism’s chance of survival
or ability to reproduce– adaptations
– The ability of an individual to survive and
reproduce in its specific environment –
fitness
Descent With Modification
• Over time, natural selection has
produced species that are
different than their ancestors
• Looking backwards in time you
should find the common ancestor
of all living things – common
descent
Darwin’s
Tree of
Life
Tree of Life
Evidence of Evolution
Fossil Record
• Darwin believed that life on Earth
has been evolving for millions of
years
• Darwin saw the fossil record as
a detailed record of life on
Earth
Evidence of Evolution
Geographic Distribution of
Living Species
• Darwin found that organisms living
under similar ecological conditions
end up evolving similarities without
being related – Convergent
Evolution
• Ex – Fish and whales
Convergent Evolution
Adaptive Radiation
(Divergent)
Adaptive radiation
• A species can diversify enough over time to become
entirely different species
– There are 14 species of small land birds of the
Galápagos Islands.
– All the finches derive from a single species of grounddwelling, seed-eating finch that probably emigrated
from the South American mainland.
– Because the environmental niches, or habitats, were
unoccupied on the isolated islands, the ancestral
stock was able to differentiate into diverse species;
• 3 species are ground-dwelling seedeaters,
• 3 live on cactus plants and are seedeaters,
• 1 is a tree-dwelling seedeater, and
• 7 are tree-dwelling insect eaters.
Evidence of Evolution
• Homologous Body structures
* The limbs of birds, reptiles, and
mammals may have different looks but
they form from the same embryonic
tissue – Divergent Evolution
* Similarities of Early Development
* Animals have similar embryological
development
Homologous Structures
Turtle
Alligator
Typical primitive fish
Bird
Mammals
Embryonic Development
Summary of Darwin’s
Theory
1. Variations are inherited
2. In nature, tendency towards
overpopulation
3. Not all organisms survive –
compete for resources
4. Natural Selection– struggle
for existence
Summary of Darwin’s
Theory
5. Individuals best suited to their
environment survive and
reproduce most successfully
6. Species change over time
7. Populations today come from
modifications of species of the
past
8. All organisms are united into a
single tree of life by common
decent
Allelic frequency
• The number of times an allele appears in
the gene pool
http://www.thetech.org/ge
netics/news.php?id=13
• Gene pool- all genes including all the
different alleles for that gene that are
present in a population
• Gene pool can be affected by:
• Genetic drift
– Chance occurrences change the allelic
frequencies in a population
– Happens most often in small populations
• Equal number of red worms and yellow worms
• Someone steps on the yellow worms, only red
worms left to pass on red worm allele
Genetic equilibrium
• Situation in which allelic frequencies
remain constant unless one or more
factors causes them to change
• To maintain equilibrium requires
1. random mating
2. very large population
3. no movement into or out of population
4. no mutations
5. no natural selection
Not met = evolution