Transcript Natural Selection - RMC Science Home

Natural Selection
The Origin of Species
• On the Origin of Species by
Means of Natural Selection or
the Preservation of Favoured
Races in the Struggle for Life
• This is quite a title!
• But it does suggest that
Natural Selection must play
an important role in the
creation of new species
But what is natural selection?
• Natural Selection is the way in which nature
favours the reproductive success of some
individuals within a population over others
• In other words, some individuals are more
likely to pass their genes along than others
How Natural Selection
Works
• Success can take many
forms
1. Better suited to
gathering resources in a
population
2. Better able to avoid
predators
3. Ability to adapt to a
unique environment
• There is no single recipe for
success
1. Gathering Resources
• Cheetahs
• A faster cheetah is more
likely to catch its prey than a
slower cheetah
• Faster cheetahs are more
likely to eat regularly and
stay alive
• So on average, faster
cheetahs are more likely to
reproduce and will have
more offspring than slower
cheetahs
1. Gathering Resources
• Darwin’s Finches
• Variation in the size and
shape of beaks
• Each species has evolved
to feed on unique things
• Differences in diet mean
that they do not
compete with each
other for resources
1. Gathering Resources
• Anteaters
• Ant colonies can be large tunnel complexes
• Ancestors of anteaters with longer noses and tongues found it
easier to eat ants directly out of the colony
• They were more likely to pass their genes and anteaters now
have very long noses and tongues
2. Avoiding Predators
• Camouflage
• The ability to blend in with
surroundings provides an
advantage in evading
predators
• An insect that looks more like
a leaf, for example, than
another is more likely to be
mistaken for a leaf and more
likely to be ignored by a
predator
• This camouflage is more likely
to be passed along to future
generations
Example of Camouflage
• Common Potoo
2. Avoiding Predators
• Cactus
• Found mostly in dry, arid
places
• Waxy coating helps keep water
from evaporating
• Animals living in the desert eat
plants for moisture
• Cacti have developed spikes to
deter predators
• Since cacti with spikes are less
likely to be eaten, they are also
more likely to breed and pass
on their genes
3. Adaptations to a Unique
Environment
• A characteristic or
feature of a
species that makes
it well suited for
survival or
reproductive
success in its
environment
3. Adaptations to a Unique
Environment
3. Adaptations to a Unique
Environment
• Fennec Fox
• Fennec foxes live in the
desert
• Have large ears to
dissipate heat
• Fennec foxes with large
ears are less likely to
over heat in the desert
and are more likely to
breed
3. Adaptation to a Unique
Environment
• Remember the cactus,
with its waxy coating?
• This coating prevents
water evaporation in a
hot, arid environment
3. Adaptation to a Unique
Environment
• The polar bear
• Among the largest bears
• Has both a heavy double layer of fur and a layer of fat
4-5 inches thick, to survive extreme cold
• They are very strong swimmers
– Why might this be important?
3. Adaptation to a Unique
Environment
• They are very strong
swimmers
– Why might this be
important?
– They live in oceanic
areas and often live
on areas of the sea
frozen only during
the winter months
• They blend well into
their surroundings,
making it harder for
prey to spot them
Predictions
• The Theory of Natural Selection allowed
Darwin to make predictions he could not
prove at the time (theory!)
• He predicted that, based on the location of
great apes today, we would find fossil
evidence of human ancestry in Africa
(biogeography!)
Predictions
• Darwin’s orchid: flower with a very long spur
– He predicted an insect must exist with a very long
proboscis, in order to pollinate it
– Madagascan Hawk Moth discovered in 1903
The Natural Selection Game
• Over the next several slides, you’ll see some
species that in some way demonstrate natural
selection
• Your job is to decide how that species has
been affected by natural selection, or to
decide which animal is most likely to pass it
genes along
Giraffe
Roses
Walking Stick
The Cobra
Blue Shark
Venus Fly Trap
Octopus
Pangolin
Buckeye Butterfly
Angler Fish
Bee Orchid
Adaptation
• A characteristic or feature of a species that
makes it well suited for survival or
reproductive success in its environment
Adaptation
• Explains why the cactus can be successful in
the desert
Survival of the Fittest
• This phrase has been used to describe
Darwin’s theory
• Is this misleading?
Types of Selection
• Directional
Selection
• Stabilizing
Selection
• Disruptive
Selection
Directional Selection
• Selection that favours an increase or decrease
in the value of a trait from the current
population average
Directional Selection
Antibiotic Resistance in
Bacteria
Stabilizing Selecton
• Selection against individuals exhibiting traits
that deviate from the current population
average
Stabilizing Selection
Birth weight in
human babies
Disruptive Selection
• Favours two or more variations of a trait that
differ from the current population average
Disruptive Selection
Rock Pocket Mouse
A Human Example
• Some populations have adapted to living at
extreme heights
• Able to survive despite low oxygen levels
"The sight of a feather in a peacock's tail,
whenever I gaze at it, makes me sick!”
Darwin
Homework Questions
• PG. 335 #2, 6, 11
• PG. 372 #17, 32