Transcript Evolution Notes - Harrison High School

Evolution
What is evolution?
• Evolution is defined as “descent with modification”
– a.k.a. “Change over time”
Leaves on trees
change color and
fall over several
weeks.
Mountain ranges
erode over
millions of years.
Over a large number of
years, evolution produces
tremendous diversity in
forms of life.
Isn’t Evolution ‘just’ a theory?
• Scientific theories are explanation that are based on
lines of evidence, enable valid predictions, and have
been tested in many ways.
• In contrast, there is also a popular definition of theory –
a “guess” or “hunch”
These conflicting definitions cause some confusion when it
comes to evolution…
Descent with modification???
• We’ve defined evolution as descent with modification from a common
ancestor, but exactly what has been modified?
• Compare these two examples of change in beetle populations. Which one
is an example of evolution?
– Beetles on a diet
• Imagine a year or two of drought in which there are few plants that these beetles can
eat.
• All the beetles have the same chances of survival and reproduction, but because of
food restrictions, the beetles in the population are a little smaller than the preceding
generation of beetles.
– Beetles of a different color
• Most of the beetles in the population (say 90%) have the genes for bright green
coloration and a few of them (10%) have a gene that makes them more brown.
• Some number of generations later, things have changed: brown beetles are more
common than they used to be and make up 70% of the population.
• Which example illustrates descent with modification—a change in gene
frequency over time?
Who is Charles Darwin?
• An English scientist
• Considered the “father of
modern evolutionary
theory”
• Studies animal and plant
life as a ship’s naturalist.
From these findings he
was able to develop his
theory of evolution
The Galapagos Islands
• Aboard the H.M.S Beagle,
Darwin traveled to the Galapagos
Islands
– The Galapagos supports a great deal
of diversity in both plant and
animal life
– Darwin studied & compared the
anatomy of many species of:
• Reptiles
• Insects
• Birds**
• Flowering plants
All of which were unique to the
island, but similar to species found
around the world
Darwin notices struggles
• Competition for space & food
–
–
–
–
Need to escape from predators
Need to find enough prey
Ability to find AND secure shelter
SURVIVAL OF THE FITTEST…
What is Natural Selection?
• Natural selection is one of the basic mechanisms of
evolution, along with mutation, migration, and
genetic drift.
• Darwin’s grand idea of evolution by natural
selection is relatively simple but often
misunderstood.
To find out how Natural Selection
works, imagine a population of beetles:
• There is variation in traits.
– For example, some beetles are green
and some are brown
• There is differential reproduction.
– Since the environment can’t support
unlimited population growth, not all
individuals get to reproduce to their
full potential. In this example, green
beetles tend to get eaten by birds and
survive to reproduce less often than
brown beetles do.
To find out how Natural Selection works,
imagine a population of beetles (continued…)
• There is heredity.
– The surviving brown beetles have
brown baby beetles because this trait
has a genetic basis.
• End result:
– The more advantageous trait, brown
coloration, which allows the beetle to
have more offspring, becomes more
common in the population. If this
process continues, eventually, all
individuals in the population will be
brown.
Natural Selection Overview
• In nature, there is a tendency
towards the overproduction of
offspring
• In any population of organisms,
individuals will exhibit slight
variations
– Individuals with variations that are
favorable for a particular environment
are more likely to survive and pass
those variations on to the next
generation than are individuals with
less-favorable variations
– Gradually, offspring of survivors will
make up a larger proportion of the
population and eventually a population
may look entirely different
What is fitness?
• Biologists use the word fitness to describe how
good a particular genotype is at leaving offspring
in the next generation relative to how good other
genotypes are at it.
The brown beetles have a greater fitness
relative to the green beetles.
• Fitness is a relative thing. A genotype’s fitness
depends on the environment in which the
organism lives.
Fitness in Nature
C
A
B
Caring for your offspring (A), and producing
thousands of young — many of whom won't survive
(above right), and sporting fancy feathers that attract
females (left) are a burden to the health and survival
of the parent. These strategies do, however, increase
fitness because they help the parents get more of their
offspring into the next generation.
Mechanisms of Evolution
• Mutation
– A mutation could cause parents with
genes for bright green coloration to have
offspring with a gene for brown
coloration.
– That would make the genes for brown
beetles more frequent in the population.
• Migration
– Some individuals from a population of
brown beetles might have joined a
population of green beetles.
– That would make the genes for brown
beetles more frequent in the green beetle
population.
Mechanisms of Evolution
• Genetic Drift
– Imagine that in one generation, two brown
beetles happened to have four offspring
survive to reproduce.
• Several green beetles were killed when
someone stepped on them and had no
offspring.
• The next generation would have a few more
brown beetles than the previous generation—
but just by chance.
• These chance changes from generation to
generation are known as genetic drift.
• Natural Selection
– Imagine that green beetles are easier for birds
to spot (and hence, eat).
• Brown beetles are a little more likely to
survive to produce offspring.
• They pass their genes for brown coloration on
to their offspring.
• So in the next generation, brown beetles are
more common than in the previous
generation.
Evolution Mechanisms Understood
• Mutation…
• Migration…
• Genetic Drift…
• Natural Selection…
– All of these mechanisms can cause changes in the
frequencies of genes in populations, and so all of them
are mechanisms of evolutionary change.
– However, natural selection and genetic drift cannot
operate unless there is genetic variation—that is, unless
some individuals are genetically different from others.
•If the population of beetles were 100% green, selection and
drift would not have any effect because their genetic make-up
could not change.
Natural Selection & Adaptation
•Adaptation
– Any trait that aids the chances of survival and
reproduction of an organism
– Can be explained by applying Darwin’s theory
of natural selection
– We will focus on two types of adaptations:
•Structural
– Changes in the structure of body parts
•Physiological
– Changes in an organism’s metabolic processes
Structural Adaptations
• Can be used as defense
mechanisms
– Mimicry
•A structural adaptation that
provides protection for an
organism by copying the
appearance of another, more
threatening, species
– Camouflage
•A structural adaptation that
enables an organism to blend
in with its surroundings
Non-poisonous
king snakes
mimic
poisonous coral
snakes.
Katydids have
camouflage to
look like leaves.
Physiological Adaptations
• Anti-biotic implications
– Individual bacteria in a population show variation
– Some bacteria possess a gene that makes them resistant to some
antibiotic
– When the population is exposed to the antibiotic, some
individuals die, but resistant bacteria survive
– Resistant bacteria survive and reproduce
– In time, the entire population is resistant to a certain antibiotic
“Why does Evolution matter NOW?”
http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1notes.html
“The Evolution of Antibiotic Resistance”
http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1.html
“Why does Evolution matter
NOW?” Video Questions
http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1notes.html
1.
Why is the Russian prison system considered to be "ground
zero" in the fight against TB?
2.
What is responsible for the evolution of TB strains that are
resistant to multiple drugs?
3.
How does the misuse of antibiotics affect the evolution of
disease-causing bacteria? Use the theory of natural selection to
explain the growing resistance to antibiotics.
4.
Why should we care about a resistant strain of TB in Russia?
Evidence for Evolution
• Fossils can show evolutionary changes
over time
• Anatomical structure indicate
evolutionary relationship
– Analogous structures show similarity in
structure based on adaptation for the
same function, not common descent.
• Functionless structures indicate
evolutionary pathways
– Seemingly functionless parts are called
vestigial organs or structures.
Evidence for Evolution
• Embryological development
shows evolution from a common
ancestor
– Structures that are embryologically
similar, but have different
functions, are called homologous
structures.
• Genetic comparisons may reveal
hidden relationships.
• Amino acid sequences are similar
in related organisms!
Jean Baptiste Lamarck
• French Biologist
• Believed in SPONTANEOUS
GENERATION
• Believed that living things evolved in a
continually upward direction, from dead
matter, through simple to more complex
forms, toward perfection
• Believed that organisms altered their
behavior in response to an environmental
change; these changes caused modification
to their organs & internal structure. He
further believed that these modifications
were inherited by the organism’s offspring
• Didn’t believe that species died out in
extinctions, but instead they changed into
other species