Transcript Evolution: Descent with Modifications

Evolution: Descent with Modifications
Evolution is a process….
that has transformed life on Earth from its
earliest forms to the diversity seen today
Historical context:
• Classic Greek philosophers / Biblical ideas
• Linnaeus develops taxonomy to organize life, gives
us the system of binomial nomenclature.
• Hutton saw “gradualism”, natural changes over long
time periods caused Earth’s geological changes
• Lyell supported uniformitarianism- geological
processes today are the same as those from the
past changing geology. Determined Earth was older
than 6000 as previously thought.
A Role For Fossils
• Lamarck, a French biologist at a Natural History
Museum, compared fossils to living species.
• He developed two concepts:
• Use/ disuse theory….Body parts used extensively
become larger and stronger; those parts not used
decrease is size.
• Organisms could pass acquired physical changes
onto their offspring.
• Lamarck is remembered for his explanation of
the giraffe
***BEWARE OF USING GIRAFFE EXAMPLES IN
ESSAYS on evolution!
• Although Lamarck was wrong he did attempt
to use the fossil record to explain Earth’s
diversity of life. Lamarck also recognized this
required gradual, evolutionary change over
very long periods of time.
Charles Darwin (1809-1882)
Development of Darwin’s theories:
• As Naturalist on HMS Beagle, Darwin was
given the freedom to explore exotic and
diverse species of plants and animals on South
American coastlines.
• Darwin noted species were vastly different in
South America than in Europe, even thought
the habitats were similar.
• Even the fossil record indicated species
diversity.
Visiting the volcanic Galapagos Islands 900 km
off the coast of South America led Darwin to
hypothesize the original island inhabitants came
from mainland South America.
Darwin saw a relationship between the origin of
new species and adaptations of species to the
environments .
Adaptations are the result of evolution
Adaptations usually occur because a gene mutates
or changes by accident! Some mutations can help an
animal or plant survive better than others in the
species without the mutation.
Darwin’s
Finches…..
• Darwin noted 13
varieties of finches
on the Galapagos
Islands. The finches
had special physical
adaptations allowing
them to eat the
varieties of foods
found specifically on
their home island.
Alfred Wallace, naturalist traveling in the East Indies, was
developing similar ideas about natural selection and sent his
manuscript to Darwin in 1858. As a result Darwin decided to
published his book , The Origin of Species , in 1859.
He accumulated great support for his ideas and presented
strong logical arguments for his conclusions.
Darwin is credited with developing the theory of evolution by
a process known as NATURAL SELECTION.
1) Descent with modification
1) Organisms share a common ancestry
in their remote past.
2) Descendents of this common ancestor
accumulated diverse adaptations allowing
them to survive and reproduce best in their
varying habitats.
3) The mechanism of evolution is known as
Natural selection .
Artificial vs Natural Selection
• Artificial selection ( selective breeding) —
Purposeful crosses between animals or plants
to produce a set of desired characteristics.
This helps scientists understand how nature
could cause changes in populations over time.
• Natural selection—The environmental
conditions determine which individuals in a
population produce are best adapted and will
leave the most offspring.
Natural Selection :
The Basic Observations
1)
2)
3)
4)
Species have the potential to produce large
numbers of offspring.
Environmental resources are limited.
These conditions lead to a struggle to survive
between individuals within a population.
Individuals have different genetic phenotypes.
Those with traits best suited for their
environment will likely survive to reproduce
and leave more offspring.
The Guppy Experiment:
• Female guppies prefer colorful males for mating
purposes. Predatory fish also "prefer" colorful males as
a source of food that is easy to spot. Not surprisingly,
males in locations where there are more predators
tend to be less colorful.
• Dr. Endler transferred predatory fish to regions with
brightly colored male guppies. Selection acted rapidly
and produced a guppy population with duller males.
This experiment demonstrated that variation within a
population provides the raw material for rapid
evolution when environmental conditions change.
What evidence supports evolution?
• Homologous Structures
• Fossil Record
• Vestigial Structures
• Molecular Evidence
Convergent Evolution
• Convergent evolution
is the process
whereby organisms
not closely related
independently evolve
similar traits as a
result of having to
adapt to similar
environments or
ecological niches.
Biogeography is the
study of the
distribution of species
and ecosystems in
geographic space and
through (geological)
time. Organisms and
biological communities
often vary in a regular
fashion along
geographic gradients of
latitude, elevation,
isolation and habitat
area.
Endemism
A species is unique to a defined geographic
location, such as an island, nation, country or
other defined zone, or habitat
Evolutionary Tree
An evolutionary tree represents the evolutionary relationships among a
set of organisms or groups of organisms, called taxa.
• Tips of the tree represent groups of descendent taxa (often species).
• The nodes on the tree represent the common ancestors of the
descendants.
• Many phylogenies also include an outgroup — a taxon outside the
group of interest.
GEOGRAPHIC VARIATIONS
• Any variation of a species
which is dependent on
climate or other
geographical conditions.
• Understanding how initial
population size, gene flow,
mutation frequency, and
environmental (abiotic)
factors give rise to and
maintain geographical
variation can shed light on
direction and rate of
evolutionary change
Mutations:
• Mutations rates are rare
for a given gene.
• The cumulative effect of
ALL mutations in the
genome of an individual
can be significant .
• Mutations serve as the
source of genetic
variation , thus the raw
material for natural
selection in populations.
POPULATION:
• all the organisms of the same group or
species, which live in a particular
geographical area, and have the capability of
interbreeding.
Gene Pool
• the set of
all genes, or
genetic
information
in any
population
Genetic Drift
A change in the gene
pool of small
populations due to
random chance.
Several mechanisms
can cause this :
1) Bottleneck Effect
2) Founders Effect
Founder Effects
• Sometimes one or a few individuals disperse
and become the founders of a new, isolated
population at some distance from their place
of origin
• Since these individuals may not represent all
of the alleles present in the original
population, alleles are lost and frequencies of
alleles changed. Examples include:
• Darwin’s finches
• the blue people of Kentucky
The Bottleneck Effect
• Even without movement, populations can be
drastically reduced in size
• Flooding, drought, epidemic disease, other
natural forces or progressive changes in the
environment are all causes
• the few survivors represent a random genetic
sample of the original population
• the resultant loss of genetic variability has
been termed the bottleneck effect
The Bottleneck Effect
• This process transfers alleles from one
population to another, changing the allele
frequency.
• Gene flow tends to REDUCE the differences
between the various populations.
Relative Fitness
• The survival and/or reproductive rate of a
genotype (or phenotype) relative to the
maximum survival and/or reproductive rate
of other genotypes in the population.
• Directional
selection—acts to
eliminate one
extreme from an
array of phenotypes
• Selection has
changed the
population in the
direction of lower
light attraction
toward light.
• Stabilizing
selection—selection
acts to eliminate
both extremes; it
favors an optimum
condition and
increases the
frequency of the
already common
intermediate type,
making it even more
common by
eliminating the
extremes.
Comparing Graphs Of Selection Types:
SEXUAL SELECTION
• A mode of natural
selection where members
of one sex choose mates of
the other sex with whom
to mate setting up
competition between
members of the same
sex to sexually reproduce.
SEXUAL DIMORPHISM
• the differences in
appearance between
males and females of
the same species
INTRASEXUAL VS INTERSEXUAL
Mate choice by males or females is
intersexual selection.
Male-male competition for access to mates is
the major form of intrasexual selection
Adaptive Radiation
• A process in which
organisms diversify
rapidly into a multitude
of new forms,
particularly when a
change in the
environment makes
new resources
available, creates new
challenges and opens
environmental niches.
Divergent Evolution
• As related species change over time the genetic
differences between them grow larger. The longer their
genetic lines have been separate the more differences
are visible in their DNA and proteins.
Coevolution
Co-evolution occurs when, in adapting to their
environments, two or more organisms evolve together.
To "make the best of" where they live, organisms make
use of other organisms by eating them, living on or in
them, and/or building a "partnership" with them.
Parallel Evolution
–Related organisms evolve
similar structures to be
used in similar ways. For
example, the feeding
structure in different
species of crustaceans came
from mutation of pair of
legs, turning into mouth
parts.
Evolution can lead to speciation
• Allopatric Speciation – Breeding is prevented
due to some physical barrier and varying
conditions.
• Sympatric Speciation–Breeding is prevented
even though there may be no physical barrier
to the process.
• Selective breeding – Nonrandom breeding
selects for or against certain traits .
Reproductive Barriers
• A collection of
mechanisms, behaviors
and physiological
processes that prevent
the members of two
different species that
cross or mate from
producing offspring, or
ensures that any
offspring that may be
produced are sterile.
Pre-zygotic Barriers
• Prevent the formation of
zygotes:
– Habitat Isolation
– Temporal Isolation
– Behavioral Isolation
– Mechanical Isolation
– Gametic Isolation
Post-zygotic IsolationPrevent zygote from reproducing:
– Hybrid embryos
do not correctly
develop
– Hybrid adults are
sterile (reduced
fertility)
– Hybrid individuals
do not survive to
adulthood.
IMPORTANT FACTS :
• Evolution acts on populations NOT on individuals.
• Natural Selection can only work on traits that can
be passed from generation to generation.
• Natural selection IS A PROCESS used to bring about
evolution.
• Adaptations are a result of natural selection.
• EACH of these mechanisms of change is that
populations gradually move toward increasing
the number of individuals with advantageous
characteristics.
• These individuals strengthen the population.
• The end result is a population evolves to be
adapted to its local environment.
Evolution Sample AP Test
questions
1. The different species of finches on the
Galapagos Islands are believed to have arisen
as a result of the natural selection acting on
populations that experienced
1.
2.
3.
4.
5.
Convergent evolution
Gene flow
Geographic isolation
Behavioral isolation
Hardy Weinberg Principles
2. The wing of a bat, the flipper of a whale and the
forelimb of a horse appear very different, yet
detailed studies reveal the presence of the same
basic bone pattern. These structures are examples
of
a)
b)
c)
d)
e)
Analogous structures
Homologous structures
Vestigial structures
Balanced polymorphism
Convergent evolution
1992 Essay Question :
4. Evolution is one of the major unifying concepts
of modern biology.
a. Explain the mechanisms that lead to
evolutionary change.
b. Describe how scientists use each of the
following as evidence for evolution.
(1)
(2)
(3)
Bacterial resistance to antibiotics
Comparative biochemistry
The fossil record
PRACTICDE AT HOME – A SHORT ESSAY:
Provide an example from molecular
evidence ( DNA sequencing), the fossil
record, homologous structures and
embryology to support the Modern
Theory of Evolution.
Take 5 and 7 minutes to respond to this
question.