Download Evolution and Charles Darwin

Evolution, Natural
Selection, and
Adaptations
Charles Darwin BrainPOP
Voyage of
Darwin
• In the early 1800’s most scientists thought that species were
unchanging.
•In 1831, Charles Darwin was traveling around Galapagos Islands,
he collected specimens and made observations that led him to
believe that species changed over time.
So what did Darwin Say?
► Individuals
in a population vary in their traits
(characteristics); parents pass traits to their
offspring.
► Species generally are best suited for their
environments.
► Individuals compete over resources when
resources become limited.
► Individuals with slightly better adaptations would
get more food and are more likely to reproduce
and raise their young to maturity.
Darwin’s Finches
•On the Galapagos Islands near Ecuador he
noticed something about the finches (birds).
They were all similar, but had different beaks
because they ate different foods.
Any predictions why this was?
► The
finches all came from a common
ancestor.
► As they migrated to different areas,
their food source changed.
► The birds with the most adapted beak for
that food source reproduced more often,
making that bird type more common.
► This is evolution.
Evolution
• Evolution = a change in species over time
How does evolutionary change happen?
• 1859 Darwin finally published “On
the Origin of Species”
• In the book he proposed evolution
happened through Natural Selection.
• Natural Selection = Organisms best
suited to their environment will survive
and reproduce
Natural Selection BrainPOP
How Natural Selection Causes Evolution
•Species = a group of organisms that
can interbreed and have fertile
offspring
• Population = a group of one species
living in the same place at the same
time
Natural selection is a process that
happens to populations, not
individuals.
•
• Natural selection occurs when the
environment “selects or influences”
which species within a population will
survive and reproduce based on
favorable traits.
Population vs. Individual
• Changes in genes (variations) happen to
individuals within the population. We can see
the variations of traits among different
individuals.
• Changes in gene frequencies (how often we see
the change) happen to populations. Therefore,
evolution happens to populations
How can we measure evolution?
• A gene pool is all the genes that exist in a population
• This means all of the possible alleles in a given species
at a given place and time.
• The allele frequency is how
often the allele or the gene it
codes for shows up in a
population
Mechanism for Natural Selection
• Living things are constantly struggling to
survive.
• Those with variations (traits) best suited to
the conditions of their life and environment are
most likely to survive and reproduce.
("survival of the fittest").
• Genetic variations that cause a species to be
successful will be passed on to their offspring.
Natural Selection vs. Artificial Selection
• Artificial Selection- man selects a
trait.
Ex) Selective breeding- people select
favorable traits in plants and animals to
pass to future generations
• Natural Selection- nature selects the
trait
Ex) Survival of the Fittest- The ability
to survive and reproduce in your
environment.
Fitness
The result of natural selection will always
improve the fitness between species and its
environment using adaptations.
• Fitness is a measure of reproductive success.
• Those individuals who have the largest number
of MATURE offspring are the most fit.
•
Adaptations
• In natural selection, if nature doesn't
“select” or work for the traits you
inherited, your species has to options:
Die Out or Adapt.
• Adaptations are inherited
structures or behaviors
that help organisms
survive and reproduce.
• Adaptations are caused by mutations.
Adaptations Video
Evolution-related Scientists:
►
►
►
►
►
►
James Hutton - Geographical forces shaped the
earth and it is millions of years old.
Thomas Malthus - His essay proposed that earth’s
population will outgrow its resources.
Jean-Baptiste Lamarck - One of the first to propose
that organisms change over time.
Charles Darwin - Sailed on the H.M.S. Beagle,
proposing evidence for Evolution.
Charles Lyell - Principles of Geography better
explained the age of the earth.
Alfred Wallace - Collaborated with Charles Darwin,
presented to the Linnaean Society
Examples of Adaptations
and Natural Selection
Types of Natural Selection
• Stabilizing Selection
• Favors maintaining allele frequencies
• Selects against extreme phenotypes
Examples of Stabilizing Selection
• Humans
• Babies born at very high and very low birth weights
are less likely to survive.
• Plants
• Plants in a population that are very short may not
receive as much sunlight. Plants that are very tall
may be more susceptible to wind damage.
• The number of plants of medium height will
increase while the numbers of short and tall plants
will decrease.
Types of Natural Selection
• Directional Selection
• Favors one phenotype over another
• Caused by changes in environment (weather,
food availability, drought or flood).
A
B
Phenotype B favored over A
Examples of Directional Selection
• Finches
• Under conditions of drought, larger birds are more
likely to survive than smaller ones.
• Birds with larger beaks are more likely to survive
than birds with smaller beaks.
• Allele frequencies for the
population (not individual
birds) will change.
Types of Natural Selection
• Disruptive Selection
• Selects for extreme phenotypes and against
“average.”
• This can lead to speciation – the process of new
species arising
Example of Disruptive Selection
• This grass is pollinated by three different pollinators, one
that was attracted to short plants, another that
preferred plants of medium height and a third that visited
only the tallest plants.
• If the pollinator for medium height
disappeared from an area,
medium height grass would
be selected against.
• The population would have
both short and tall, but not medium
height plants.
• Allele frequencies for the population (not individual plants)
will change.
Webbed feet in Ducks
• Originally a mutation caused the ducks
to have webbed feet. Because ducks
live in water, the mutation was
advantageous.
• Ducks with the mutation were
more likely to survive and
pass the mutation to the next
generation of ducks.
Syndactyly in Humans
• Did you know that other animals have
mutations for webbed hands or feet?
• In humans it is called syndactyly, and it
occurs in approximately 1 in 2,000 to 2,500
live births.
Syndactyly in Humans
• Syndactyly in humans is a dominant allele.
• Dominant alleles are always expressed (AA or Aa).
• There is no environmental advantage. Webbed toes
or fingers do not make humans better able to survive
and reproduce in their environment.
• Even though the gene for syndactyly is dominant, it
has not ever been found in high frequencies because
it is not considered favorable.
• People have chosen (or selected) not to marry into
families with less desirable traits.
Arctic Animals Have Adapted to Reduce Heat Loss
Animals in really cold conditions need to keep warm!
• Small surface area to volume: Have a compact rounder
shape which keep their surface area to a minimum and
reduces heat loss.
• Well Insulated: Thick layer of blubber for insulation and
stores energy when food is scarce. Thick hairy coats
keep body heat in and greasy fur sheds water.
• Good In Snowy Conditions: White fur for camouflage.
Big feet spread weight and prevents sinking in snow or
breaking thin ice.
Brain Pop: Camouflage
Adaptations to Deter (discourage) Predators
• Some plants and animals
have armor- like thorns,
spines and hard shells
• Others produce poisons –
like bees and poison ivy
Red near yellow
will “Kill-a-Fellow”
• Some have warning colors
to scare off predators –
like wasps.
Red near Black is
a “Friend-of-Jack”
More examples of
adaptations that prove
natural selection is the
reason behind evolution.
Example 1: Antibiotic Resistant Bacteria
• Bacteria can become resistant to antibiotics
• If someone gets sick they might be given an antibiotic
which kills 99% of the bacteria
• The remaining 1% that survive are resistant, so when
they reproduce they are passing on the resistant gene
• If someone gets sick with the resistant bacteria then the
antibiotic will not help them
Antibiotic
Resistance
BrainPOP
Example 2: Peppered Moth
• Until the 1850’s dark gray moths
were rare. Almost all moths were
pale white.
• In 1850 dark moths started to
become more common, usually in the
highly industrialized areas with
smoke emissions. WHY?
Pale tree trunks were made black
by the pollution from the factories
and dark moths sitting on these trees
were better camouflaged from their
predators and lived on to reproduce
more black moths.
Example 3: Rats Adapt to Beat Poison
The poison warfarin was
widely used to control the
rat population. However, a
certain gene gives rats
resistance to it, so rats
which carry it are more
likely to survive and
reproduce. The gene has
become more frequent in
the rat population, so
warfarin is not used as
much any more.
Scientists
►
1785 - James Hutton – Proposed that the Earth is millions not thousands of years
old.
►
1798 – Thomas Malthus –Predicted that the human population will grow faster than
the space and food supplies needed to sustain it.
►
1809 – Jean-Baptiste Lamarck – Through the use or disuse of organs, organisms
acquired or lost certain traits in their lifetime. The ideas are flawed but he is the
first to propose a mechanism explaining how organisms change over time.
►
1831 – Charles Darwin – “The Father of Evolution” published a book entitled “On
the Origin of Species” in which he described evolution, natural selection, and
fitness.
►
1833 – Charles Lyell – Lyell explained that scientists should use current processes
to explain past events in geology because processes occurring now have shaped
Earth’s geological features over long periods of time.
►
1858 – Alfred Wallace – Based on his studies with plants and animals, Wallace said
that the most fit of a species survived and that the traits which enabled them to
survive were then passed down to future generations eventually creating a new
species. Agreed with natural selection and evolution.