How Traits Change Over Time
Cats which are small
and not aggressive
and can play
the piano?
How man has changed
the traits of organisms through
Artificial Selection.
Dogs have been breed to be friendly
Gold-colored fish
Cows to produce
more milk
Horses for speed
If you wished to breed the fastest
racehorses, how would you do it?
You would probably mate your fastest male
and female horses knowing their offspring
should also be fast. If you continued to breed
only the fastest horses generation after
generation, soon you will have horses ready to
race in Churchill Downs.
If you wished to breed the prettiest
guppies, how would you do it?
By only selecting the most colorful guppies
and those with the longest tails, then
breeding them generation after generation.
wild guppies
Guppy which has been
selectively bred.
Dog breeders have been selectively
breeding for desirable traits for centuries.
• To try your hand at
artificial breeding,
check out the
hyperlink below.
• Scroll down the page
to the online activity,
Dog Gone Perfect
Laboratories.
• Dog Gone Perfect
Laboratories Hyperlink
Have you tried this activity?
After many generations, the offspring may look
very different from their ancient ancestors.
Farmers have cultivated many popular
vegetables from wild mustard,
by artificially selecting for certain attributes.
In essence, when humans selectively
breed organisms for certain traits,
they are selecting for certain genes.
Charles Darwin
From 1831 to 1836 Charles
Darwin served as a naturalist
aboard the ship H.M.S.
Beagle on a British science
expedition around the world.
While in the Galapagos
Islands in the Pacific Ocean
he wondered about the
origins of the many variations
of plants and animals he
collected there.
He wondered if nature could select
for certain traits in the same way that
man selects for certain traits.
Can you find the animals in the pictures below?
Through observation and study, Darwin noted
that organisms produce many more offspring
than can possibly survive in nature.
For example, salmon typically lay ~10,000
eggs, however, only a few will survive to
adulthood and reproduce.
Putting these facts together, Darwin
discovered one of the most important
ideas in biology--
Natural Selection.
Natural Selection
The idea of natural selection is a very simple one.
It really comes down to two undeniable facts and
one inescapable conclusion:
Fact (1) Organisms vary and
these variations (genes)
are inherited by their
offspring.
Fact (2) Organisms produce more offspring than
can possibly survive in nature. As resources
become scarce, individuals must compete with
each other to survive. Most organisms will not
make it to adulthood, and therefore very few will
breed and pass on their genes.
Thousands of frog eggs are laid in clumps in
a fresh water pond. Each clump is laid by
one female. Few will survive to adulthood.
Apple trees produce far more seeds
than could possibly survive to
become full grown trees.
Remember this story?
CHARLOTTE'S WEB ends in the springtime, as tiny
spiderlings emerge from Charlotte's egg case. The gray orb
spider called her egg sac her magnum opus, Latin for "great
work." Charlotte told her friend Wilbur the pig that the egg
sac held 514 eggs and would hatch in the spring. Her friend
Wilbur the pig patiently waited, and this was his reward:
Up, Up and Away!
Wilbur was surprised and amazed when they hatched out,
and even more surprised and amazed a few days later when
they did something he'd never imagined they would do. One
spring day, a warm draft of rising air blew softly through the
barn cellar. The baby spiders felt the warm updraft and one
of Charlotte's children climbed to the top of the fence. The
spider let loose a cloud of fine silk that formed a balloon. It
was time for the baby spiders to set forth as aeronauts. They
were going into the world on a warm updraft to make webs
for themselves. The air was soon filled with tiny balloons,
each balloon carrying a spider.
CHARLOTTE'S WEB is fictional, but baby spiders really
do balloon through the air usually by the thousands.
In reality, few of those baby spiders will survive to
adulthood. Many will be eaten by predators; some will
not find enough to eat and starve.
So what was special about those few who survive?
-Maybe their coloration blended into the environment
better than their brothers and sisters, so they avoided
hungry birds.
-Maybe they built better webs than their brothers and
sisters and avoided starvation.
This leads to one inescapable conclusion....
Inescapable conclusion:
Those offspring that do survive are best adapted
to their environment and will pass their genes on
to their offspring.
The result is, over time, populations of organisms
become better adapted to their environment by
this process of natural selection.
For example, this species of insect is well
adapted (carries the right genes) to blend into its
environment.
Do you see the walking stick insect?
It received those genes from its parents, whose genes
were successful enough to allow them to survive
long enough to breed.
Natural selection in action-The Manchester peppered moths
“Before the Industrial Revolution, the peppered moth
was mostly found in a light gray form with little black
speckled spots. The light-bodied moths were able to
blend in with the light-colored lichens and tree bark,
and the less common black moth was more likely to
be eaten by birds. As a result of the common lightcolored lichens and English trees, therefore, the
light-colored moths were much more effective at
hiding from predators,
and the frequency of the
dark allele was about 0.01%.
Light-colored moth
Dark moth
During the early decades of the Industrial Revolution
in England, the countryside between London and
Manchester was blanketed with soot from the new
coal-burning factories. Many of the light-bodied
lichens died from sulfur dioxide emissions, and the
trees became covered with soot. This led to
an increase in bird predation for
light-colored moths, as they no
longer blended in as well in their
polluted ecosystem: indeed, their
bodies now dramatically contrasted
Dark moths on light
with the color of the bark.
colored bark are
easy targets for hungry
Dark-colored moths, on the other
birds but are
hand, were camouflaged very well hidden on pollution
darkened trees.
by the blackened trees.
Although a majority of light-colored moths initially
continued to be produced, most of them didn't survive,
while the dark-colored moths flourished. As a result,
over the course of many generations of moths, the
allele frequency gradually shifted towards the
dominant allele, as more and more dark-bodied moths
survived to reproduce. By the mid-19th century, the
number of dark-colored moths had risen noticeably,
and by 1895, the percentage of dark-colored moths in
the Manchester peppered moth population was
reported at 98%, a dramatic change (by almost
1000%) from the original frequency.
In modern times, due to cleaner air standards, the
dark-bodied moth is becoming less frequent, again
demonstrating the adaptive shifts in the peppered
moth population.”
-From Wikipedia, the free encyclopedia
Natural selection in action-The Manchester peppered moths
• Click the hyperlink below and go to
the natural selection simulation game.
• peppered moth simulation game
Note
**Run Lichen (light colored) forest
link. Record your results.
**Run Soot (dark colored) forest
link. Record your results.
Another example of natural
selection at work
(click below to watch video clip)
Note: Turn caption on while viewing
Natural Selection (in summary)
1. Organisms vary and these variations (genes)
are inherited by their offspring.
2. Organisms produce more offspring than can
possibly survive in nature.
3. Those offspring that do survive are best
adapted to their environment and will pass
their genes on to their offspring.
The result is, over time, populations of organisms
become better adapted to their environment by this
process of natural selection.
Evolution means change over time.
Cars have changed over time.
Computers have changed over time.
Video games have changed over time.
pong
Evolution
Darwin’s idea describes how life can
change over time through the mechanism
of natural selection.
Evolution is a slow process.
It is important to understand individual
organisms do not change (adapt) over time.
In general, individuals are either well adapted
(have the right genes) or die before passing
on their genes.
Only populations of
organisms evolve.
Environments change over time.
Due to the movement of continents and global climate
change, environments are constantly changing;
putting constant pressure on populations to evolve.
Populations are constantly evolving
(The Eternal Arms Race)
Click on the video below to see an
interesting case of an evolving arms race.
Assignment
• Describe the evolutionary arms race
between the poisonous newt and the
poison tolerant garner snake in terms of
natural selection.
• (See next slide for a reminder)
Natural Selection (in summary)
(apply these 3 ideas to your assignment)
1. Organisms vary and these variations (genes)
are inherited by their offspring.
2. Organisms produce more offspring than can
possibly survive in nature.
3. Those offspring that do survive are best
adapted to their environment and will pass
their genes on to their offspring.
The result is, over time, populations of organisms
become better adapted to their environment by this
process of natural selection.
Why is it important to know
about evolution?
What evolution means to us
The eternal arms racemicrobes versus medicine
click on the picture below to watch the video
Evolution by natural selection is a
central concept in biology.
While natural selection is a simple process to
understand, as it exerts it’s influence over
geologic time it’s implications are far-reaching,
subtle and profound.
It explains the unity of life and is responsible for
the enormous diversity of life on our planet.
"Nothing in biology makes sense except
in the light of evolution."
-Theodosius Dobzhansky, Geneticist
Do the natural selection web lab.
(click on the screen below)