Transcript Natural Selection and the Evidence for Evolution

Natural Selection
and the Evidence
for Evolution
Julieanne Quigley
2008
Food for Thought…
 Learning the principals of evolution
make it easier to understand modern
biology
 Charles Darwin had ideas that are
supported by fossil evidence and his
ideas are now the basis for modern
evolutionary thought
 Biologists have used fossils since the
1700’s and started forming evolutionary
ideas back then
 They wondered how fossils formed,
why they were extinct and how they
were related to modern species
 When geologists provided evidence that
earth was billions of years old, biologists
began to suspect that life evolves slowly
over time
Charles Darwin
 English scientist- 1809-1882
 He took a job at the age of 21 on
the HMS Beagle (ship) as a
naturalist
 A naturalist studies and collects
biological specimens
 He sailed to The Galapagos
Islands near the equator
 He started to see evolutionary
patterns there
What’s Next?
 For 22 years, Darwin worked to find an
explanation for how species changed
over time
 He came up with the idea of NATURAL
SELECTION
 Natural Selection is: a mechanism for
change in populations
The Rules of Natural Selection
OVERPRODUCTIONEach species
produces more
offspring than can
survive. Not all
offspring can
survive because
there is not enough
food or living space
for all
The Rules of Natural
Selection
COMPETITION There is a
struggle for existence.
The offspring of each
generation compete for
things that they need to
survive (food, water,
shelter, space, a mate).
Only a few will live long
enough to reproduce,
the others will die.
Rules of Natural Selection
VARIATION The
offspring of each
generation are not
exactly alike. For
example, some
organisms are faster or
stronger than others.
Differences in traits
among individuals of a
species are called
variations
Rules of Natural Selection
SURVIVAL OF THE
FITTEST
Some variations make
organisms better
suited for survival in
their environments.
These organisms are
more likely to survive
and reproduce
Evolution of a New
Species
Individuals with favorable variations survive
and reproduce. They pass their favorable
traits to their offspring. Therefore, their
offspring are more likely to survive and
reproduce in the next generation.
Unfavorable variations eventually
disappear. In this way, favorable
variations remain in the species. Over
many generations, these changes can
result in the appearance of a new
species.
Evidence for Evolution
AdaptationsSome organisms
have thorns and
others do not. Some
organisms have
distinctive coloring
and others do
not…these
adaptations help in
the survival of
organisms
Adaptations
Mimicry: a structural
adaptation that
enables one species
to resemble another
species. A harmless
species resembles a
harmful species.
Predators avoid it
Adaptations
Camouflage- an
adaptation that
enables a species to
blend with their
environment. This
helps them not to get
eaten.
Adaptations
Physiological
Adaptationschanges in an
organisms metabolic
processes. This
happens often in
bacteria. When
antibiotics are not
used properly,
bacteria become
resistant to
treatment.
Other Evidence for
Evolution
Fossils- Provide
information on early
life and evolutionary
history. It is possible
to conclude the
ancestors of
organisms and when
the evolution of that
species took place.
Other Evidence for
Evolution
Homologous
Structures: structural
features with a
common evolutionary
origin. The features
can be similar in
arrangement,
function or in both
Example: Animal Limbs
Other Evidence for
Evolution
Analogous structuresBody parts of
organisms that do
not have common
evolutionary origin,
but similar function
Example: wings of a
bird verses wings of
an insect
Other Evidence of
Evolution
Vestigial Structures- a body
structure that no longer
has a function in a
present day organism,
but was probably useful
to an ancestor
Example: Eyes of blind
mole rats or cave fish
(the animals are blind
but still have eyes) or
wings on flightless birds
Other Evidence for
Evolution
Embryology- Looking at the
embryo (developing
baby) at the earliest
stages of growth. The
embryos of fish, reptiles,
mammals and birds are
all very similar. All start
forming with gill slits and
tails! They develop into
different things.
Other Evidence for
Evolution
Biochemistry- reveals
information about
relationships
between individuals
and species by
comparing the DNA
and RNA
Mechanisms of Evolution
Population Genetics- populations of
organisms evolve, not individuals.
A population is all the members of a
species that live in a specific area
A populations genes can change over
time…
Population Genetics
Gene Pool- All of the alleles (gene choices)
in a specific population
Allelic Frequency- The percentage of a
specific allele or gene shows up in that
population
Genetic Equilibrium- A population whose
frequency of alleles or genes stays the
same over generations
Population Genetics
A population that is in genetic
equilibrium is not evolving.
Genetic Drift- A mechanism
that disrupts a populations
genetic equilibrium. This can
cause an increase in rare
alleles.
Example: Small Amish
population in Pennsylvania
often have 6 fingered
offspring
Natural Selection Acts on
Variations
 Variations increase or decrease an organisms
chance for survival. If a variation is helpful, it is
passed on to offspring. If it is harmful, the
organism dies and does not pass on the
variation/trait to its offspring.
Different Types of Natural
Selection
Different types of natural selection act over
the range of a trait’s variation.
PLEASE OPEN YOUR BOOK TO PAGE
416
Stabilizing Selection
Natural selection that favors the average
individual.
Consider a population of spiders where average
size is the survival advantage. Too big and
birds can see them, too small and they can’t
find food. In this environment the average
sized spider is more likely to survive and pass
on its genes
Directional Selection
When natural selection favors one of the extreme
variations of a trait
A population of woodpeckers feed on insects
living deep in the bark. Only woodpeckers with
the longest beaks could feed on that insect.
Long beaks birds would survive better than
average or small beaked birds.
Disruptive Selection
Natural selection that favors individuals with
either extreme of a trait’s variation are selected
for.
For example- a population of clams with shells of
white, tan and dark brown live on a beach. All
the rocks on the beach are either very light or
very dark. All the light clams survive on the
light rocks, and all the dark clams survive on
the dark rocks. So it is a strong disadvantage
to be tan. They can be seen on both the light
and dark rocks.
The evolution of the
species
Speciation-The evolution of new species. It
occurs when members of similar
population no longer produce fertile
offspring within their natural environment
Species- group of organisms who look
similar and can interbreed.
Causes of Speciation
Geographic Isolationwhen a physical
barrier (water,
mountain, city)
divides a population.
A new species can
evolve when a
population has been
isolated if the
conditions are
different
Causes of Speciation
Reproductive IsolationWhen formally interbreeding organisms
can no longer mate and produce fertile
offspring.
Example: one population of tree frog mates
in the fall, the other in the spring. These
two populations will not mate with each
other.
Causes of Speciation
Changes in the chromosome numbers can
cause speciation in plants. When a
mistake happens in meiosis it can result
in a polyploid individual (too many
chromosomes). This often creates bigger
fruit and flowers in plants. If this happens
speciation might occur.
Speciation can occur quickly
or gradually…
Gradualism- a new species originates out of a
slow gradual change of adaptations. Such as
camels. They evolved very slowly over
millions of years.
Punctuated Equilibrium- Species occur rapidly
in bursts with long periods of genetic
equilibrium in between. This usually happens
when the environment changes. A new
species can form in 5,000-10,000 years
Patterns of Evolution
Biologists have observed different patterns
of evolution that occur throughout the
world in different natural environments.
These patterns support the idea that
natural selection is an important agent for
evolution
Adaptive Radiation
When an ancestral
species evolves into an
array of species to fit a
number if diverse
habitats.
Example: Hawaiian
Honeycreeper birdsDiffer in beak shape
and color depending on
the flowers of the area
Divergent Evolution
Pattern of evolution
when species that
once were similar to
each other become
increasingly different
Convergent Evolution
A pattern of evolution in which distantly related
organisms evolve similar traits. It happens when
unrelated organisms share similar environmental
pressures, they share similar natural selection