Before we begin...a quick Table Top
blog
► Start at the station assigned – NO SITTING DOWN ► Write down an appropriate answer to the question
at the table OR
► Put your initials by a statement you agree with ► Rotate through each station
► You must write at least 1 statement on 1 of the
papers
► When finished, go back to assigned station
Revisit Table Top Blog
►W2L: What understanding have changed
for you from the video concerning the table top blog question?
What is a theory? What is science?
What does it mean to believe in something?
What is evolution?
What does evidence mean?
►What questions do you have about
evolution/what do you want to know?
What is evolution?
►Biological evolution, simply put, is descent
with modification. This definition
encompasses small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale
evolution (the descent of different species from a common ancestor over many
generations). Evolution helps us to understand the history of life.
What is evolution?
►Theory stating that life changes over time ►Is the basis of modern biology
►Based on a collection of evidence, and
Charles Darwin
► A naturalist who sailed on the HMS
Beagle from 1831 – 1836 around the coast of South America
► He spent 5 weeks on the different
Galapagos Islands making
observations, collecting specimen, and journaling the geological
features of the different islands
► After returning home from the 5
year journey, he was so intrigued by what he saw that he spent the rest of his life researching and
What Darwin Observed
► Species of organisms
that live no where else on earth
13 different species of finches
Marine iguanas
Giant tortoises
Galapagos penguins
Prickly pear cactus
Your Turn – What differences do
you observe?
Your Turn –
What
differences do
you observe?
► W2L: Why do you
think these animals are so different?
► W2L: How do you
think these animals got this way?
Galapagos Marine Iguana
What Darwin Observed
► The Galapagos Islands are
usually dry, harsh lands that make living on them difficult
► Because of this, Darwin
observed that species had to adapt to this difficult terrain, or die
► Certain traits the organisms
had better suited them for survival on the different islands
► He called this observation
Natural Selection
► The process by which individuals that are
better suited to their environment survive
and reproduce most successfully; also called “Survival of the Fittest”
►Natural Selection takes place without human
control or direction.
►Natural Selection cannot be seen directly; it
can only be observed as changes in a population over many successive
Mechanisms of Change
► In order for evolution to occur, there MUST be
variation in the traits of a species, one source of this is sexual reproduction
► Throughout the years since Darwin first
recognized changes in species, scientists have been able to recognize 4 major mechanisms for Evolution:
1. Natural Selection
2. Mutations
3. Genetic Drift
1. Natural Selection
There are 4 steps for Natural Selection to occur:
► overproduction of
offspring
► variations exist in
populations
► Some variations are
favorable, some are not
► Populations evolve, or
Some Clarifications…
►Individuals do NOT evolve, only
populations do and only over a number of generations.
►“Favored” means “more likely to be
passed on” not stronger, bigger, etc. (i.e., fitness = reproductive success).
►What is favored in one environment may
Natural Selection
► Adaptation - An adaptation is a
feature that is common in a
population because it provides some improved function.
Adaptations are well fitted to their function and are produced by
natural selection.
Adaptations can include structural
traits like color or shape, or it could be a behavioral trait – bird
migration, or physiological
adaptation – like a protein that works better at a certain temperature.
► Adaptations must be:
Heritable – passed on to offspring
Functional – perform the predicted function
Adaptive – it must benefit the organism
Natural Selection
►Variations are different than adaptations ►It may be good or bad
►Adaptations come from variations that are
good, and over time are inherited by all members from a population
►Adaptations are the result of natural
selection
►An organism can be thought of as a bundle
Natural Selection
►So, when people say that evolution is the
“survival of the fittest,” it isn’t exactly correct
►Natural selection does maintain populations
based on certain traits, but they may not be the best traits, just good enough
►So the saying really should go “Survival of
EXAMPLES OF NATURAL
SELECTION
►Pink River Dolphins
W2L: Pink River Dolphins
►W2L: After watching the video, do a 2
minute quick write that discusses the adaptations of the Amazon pink river dolphin and how this is an example of natural selection
►http://www.teachersdomain.org/resource/k
Industrial Melanism/ Peppered Moth-
An example of Natural Selection
► The light-colored form (typica) of the moth was the predominant form in
England prior to the beginning of the industrial revolution. The light colored moth's speckled wings are easy to spot against a dark background, but
would be difficult to pick out against the light-colored bark of many trees common in England.
► Around the middle of the 19th century, however, a new form of the moth
began to appear. This dark-colored form is known as carbonaria, and it is easiest to see against a light background. As you can well imagine,
carbonaria would be almost invisible against a dark background, just as
typica would be difficult to see against a light background.
Another example of Natural Selection
►Hummingbirds’ Bill Length
Video: How does Evolution really work anyways
?
2. Mutations
► Mutation is a change in DNA, the hereditary material of
life. An organism’s DNA affects how it looks, how it
behaves, and its physiology—all aspects of its life. So a change in an organism’s DNA can cause changes in all aspects of its life.
► Mutations are RANDOM
► Causes of Mutations
Incorrect DNA replication
Exposure to mutagens (radiation, chemicals, etc.)
Watch sickle cell anemia video:
Where does Variation in a population
come from?
►The ultimate source of all genetic variation
is mutation
►Other sources: sexual reproduction and
3. Genetic Drift
► Genetic Drift = By chance, certain genes in a
populations’ gene pool become more
common than others.
Northern Elephant seals were hunted almost to extinction. Now on the rebound, they have lost much of their genetic variety due to the fact they had so few numbers to re-populate
The same story can be told about the Giant Tortoises of the Galapagos Islands.
► Genetic drift affects the genetic makeup of the population
but, unlike natural selection, through an entirely random process. Although genetic drift is a mechanism of
evolution, it doesn’t work to produce adaptations.
Small field of white and red flowers…..
A Landslide randomly wipes out half the
population. All of the white flowers are
killed.
The future generations are all red flowers.
4. Migration
► Migration is the
movement of a
population of a species from one area to
another
► If this population mixes
Evolution Notes (cont)
Evidence supporting Evolution
►Fossil Evidence
►Anatomical Evidence
►Biogeographic Evidence ►Genetic Evidence
Video: How do we know evolution really happens.
Fossil evidence
► provides snapshots of
the past that when assembled shows
evolutionary change over the past four billion
years.
► W2L: How can you tell
the age of a fossil based on its location in rock? (remember relative
Transitional Forms
► Fossils that show the
intermediate states between an ancestral form and that of its descendants.
► numerous examples of
Anatomical evidence
►Homologous Structures-
some animals share parts that are very similar even though they may have
entirely different functions
► Vestigial structures -are body
parts that are reduced in size and appear to serve no function.
Homologies in Embryos
► Embryologic evidence
– embryos from many organisms go through very similar stages of development even
Fish
salamander
tortoise chicken pig cow rabbit
Biogeographic Evidence
► The distribution of living
things provides
information about the past histories of both living
things and the surface of the Earth.
► This evidence is consistent
Genetic evidence
► Structure of DNA in universal ► 20 amino acids
► Similarities in proteins
► Example: The hemoglobin molecule in humans is much more similar to that of a
chimpanzee than a dog
► The more similarities in protein structure/function the more
similar the DNA is between organisms
► The more similar the DNA the more closely related the
organisms are
Examples
►Video: Genetic Evidence:
►http://www.pbs.org/wgbh/evolution/library/
How do these mechanisms lead to
new species?
►A species is defined as a group of
individuals that actually or potentially
interbreed in nature. In this sense, a species is the biggest gene pool possible under
natural conditions.
►Sometimes its easy to tell the difference
between species, sometimes its not
Cocker spaniel and golden retriever? Horse and donkey?
How do new species originate?
► Speciation – when populations are isolated from each
other. This keeps the gene pools from mixing
► Isolation can be of two ways:
Geographical: physical barrier
Behavior : behavior barrier – for example, mating seasons are different
► Also known as reproductive isolation
► http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo
How long does it take for new
species to originate?
► There are different theories on the rate at
which evolution occurs and how they occur:
1. Gradualism – evolution takes place at a slow
but steady rate
2. Punctuated equilibrium – long periods of
stability interrupted by periods of change
3. Mass extinctions – something causes masses
to die off, leaving niches to be filled
► These theories are currently being researched
Some of the questions that
evolutionary biologists are trying to
answer include:
►Does evolution tend to proceed slowly and
steadily or in quick jumps?
►How does evolution produce new and
complex features?
►Are there trends in evolution, and if so,
what processes generate them?
Credits
►Many of the pictures, illustrations, and text
came from the website:
http://evolution.berkeley.edu/evosite/evohom e.html
