Transcript What is evolution?

EW: Why do organisms evolve?
Is it their choice to change?
Monday, May 12th, 2014
• LT: I will be able to discuss
the mechanisms of evolution.
Agenda:
-What is evolution? How do
organisms evolve?
-Natural selection
-peer to peer support for 3rd and
6th periods
-Hand out CH 17 and 18 V and C
Tomorrow:
-Charles Darwin’s findings
-Evidence for evolution
-species and populations
What is evolution?
1. The process whereby new species arise from
earlier species by accumulated change "descent with modification."
2. The pattern of change of life-forms over time
seen in the tree of life as developed from many
observations.
3. The mechanism for how evolution happens is
largely explained by natural selection.
4. Happens to populations not individuals
5. Can happen over a long period of time or can
happen rapidly depending on external factors
that may be promoting specific traits over others
4 mechanisms for how
Evolution works!
They are: mutation, migration,
genetic drift and natural selection
-genetic variation is another important
component and is necessary for genetic drift
and natural selection to take place
1. Mutations:
-Change in a DNA
sequence usually
because of errors in
replication or repair
- other factors such as
radiation, specific
harmful chemicals
(essentially causes DNA to
break down)
-They
are random (can
be useful, harmful or
not necessary to the
function of the
organism)
Example:
A mutation could
cause parents to have a gene
for brown coloration instead of
green. This would cause
genes for brown coloration to
be more frequent than they
were before this mutation.
2. Migration or gene flow:
-Any movement of genes
from one population to
another
-Can be very important
source of genetic
variation, especially if
those genes did not
previously exist in that
population
Example: Some individuals
from a population of
brown beetles might have
joined a population of
green beetles. That would
make genes for brown
coloration more frequent
in the green beetle
population than they were
before the brown beetles
migrated into it.
3. Genetic Drift:
-In each generation, some
individuals may, just by
chance, leave behind a
few more descendents
(and genes, of course!)
than other individuals.
-It is an entirely random
process, and therefore
does not lead to
adaptations
Example: 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.
4. Natural Selection:
-Is due to: genetic
variation and
adaptations;
differential
reproduction; and
heredity and fitness
-Nature chooses viable
traits!
Example: 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.
Ideas That Shaped Darwin's
Thinking
1. Age of the Earth - old; slow processes have and are
changing Earth (Hutton-1780s & Lyell-1830s)
Darwin - If Earth changes over time, can
life?
2. Theory of Inheritance of Acquired Characteristics individual drive toward perfection; organisms can pass
on to offspring changes they make to their bodies during
their lifetime
(Jean Baptiste Lamarck) First naturalist to hypothesize that
species are not fixed.
3. Forces work against human population growth populations can grow faster than resources to
support them; leads to disease, famine, etc.
(Malthus - 1798)
Darwin - this applies even more to nonhuman
species; provides mechanism to explain how
evolution works.
4. Artificial Selection (plant & animal breeders)
-nature provides variation; humans select those
they find useful
Darwin - nature provides the raw material for
evolution; nature selects those that will succeed
Darwin and Wallace’s Theory of
Evolution by Natural Selection
There are three main mechanisms that
influence the evolution of a species by
natural selection:
1. differential reproduction; 2. variation and
adaptation; 3. heredity and fitness.
EW: How can a species evolve?
Tuesday, May 13th, 2014
LT: I will be able to
explain the
mechanisms of
natural selection.
Agenda:
-Natural selection
-Population
-Darwin’s findings
Tomorrow:
-more evidence of
evolution
-phylogenies
Peer to peer support!
• Find someone else in
the class that you are
partnering up with for
this unit.
• During some class
time and out of class
they will help support
you with your goals!
• Get out a sheet of
paper.
• Discuss two goals
that you both have for
this unit in order to
complete the portfolio
and how you will
accomplish those
goals, write those
down and turn in to
me!
1. Differential
reproduction
(struggle for
existence) - more
offspring are
produced than the
environment can
support; this leads to
competition for
resources (food, living
space, etc.)
Example:
Green beetles tend to
get eaten by birds
and survive to
reproduce less often
than brown beetles
do.
2. Variation and
Adaptation - Within
populations, variations in
forms of traits exist. Any
heritable characteristic
that increases an
organism's ability to
survive and reproduce is
an adaptation.
-Sources of genetic
variation include
mutations, cross over,
random assortment,
sexual reproduction and
gene flow
Example: some beetles are
green and some are
brown.
Adaptation examples and nonexamples
Example:
Echolocation in bats
is an adaptation for
catching insects.
Example: Mimicry of leaves by insects is an
adaptation for evading predators. This example is a
katydid from Costa Rica.
Non-example: nonfunctional eyes
(vestigial structures)
of fish that live in
caves
3. Heredity and FitnessWell adapted
individuals are more
successful at
reproducing and,
therefore, pass their
adaptive traits on to
their offspring,
increasing the trait in
the population.
Example: The surviving
brown beetles have
brown baby beetles
because this trait has
a genetic basis.
More about Fitness
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 fittest individual is not
necessarily the strongest,
fastest, or biggest. A
genotype's fitness includes its
ability to survive, find a mate,
produce offspring — and
ultimately leave its genes in
the next generation.
Example: If brown beetles
consistently leave more
offspring than green
beetles because of their
color, you'd say that the
brown beetles had a
higher fitness.
Recap of Natural Selection:
-Natural selection is not a random process,
nature chooses
-Natural selection is not leading to perfection
and traits are only adaptive while
environmental conditions are adequate for
the survival and reproduction of offspring
What is a species?
A species is often 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.
Speciation
Speciation is a
lineage-splitting
event that produces
two or more separate
species.
How can speciation happen?
Geographic
isolation (ex.rivers,
mountains,
streams, islands)
Reproductive
isolation (reduction
of gene flow)
What are some barriers to gene
flow?
Temporal isolation (Different
reproductive time tables)
Different reproductive
timetables
Behavior isolation
The evolution of different
mating location, mating time,
or mating rituals
What is a population?
Defining populations
-It is a group of organisms that interbreed
with each other — that is, they all share a
gene pool.
-So For our species of beetle, that might be
a group of individuals that all live on a
particular mountaintop and are potential
mates for one another.
Looking at Darwin’s finches, an
example of speciation!
What Darwin hypothesized…
There was a small group of finches in Ecuador.
• A small group makes its way to the Galapagos
Islands, possibly blown in a storm or on a land
raft.
• The finches can’t get back to the mainland –
they don’t like open water.
• Darwin found 14 different species of finches,
none identical to the ones on the mainland.
Uniqueness of the finches Darwin
found
1. Had different size beaks, this was an adaptation to the food sources on
the islands
2. Many were geographically distant from each other, water separated
them; habitats were different
3. Different food on different islands
Warbler finch
Cactus finch
Woodpecker finch
Sharp-beaked finch
Small insectivorous
tree finch
Small ground
finch
Large
insectivorous
tree finch
Cactus
eater
Medium
ground finch
Insect eaters
Seed eaters
Vegetarian
tree finch
Bud eater
Large
ground
finch
EW: Look at this image. Which
candy bars are more closely
related?
Wednesday, May 14th, 2014
LT: I will be able to explain
the relationship between
cladograms and
biological evolution.
Agenda:
-Evidence for evolution
-Phylogenies or Cladogram
“Family Tree”
-What did T Rex taste like?
Tomorrow:
-Natural Selection bean lab!
Cladograms
Think about these questions while watching short
video:
1. What are cladograms?
2. What relationships do they show?
3. How do they help show evidence for evolution?
Bozeman science cladograms:
https://www.youtube.com/watch?v=ouZ9zEkxG
Wg
Go to this website
http://www.ucmp.berkeley.edu/education/ex
plorations/tours/Trex/index.html
1. Click on the student version
2. Follow along and answer questions on
the worksheet
Sexual Selection
Artificial Selection