Transcript Natural Selection

Evolution
Change Over Time
“There is no ‘Great Plan’out there to conform with
the evolutionary theory, just organisms struggling
to pass their genes on to the next generation.
That’s it.”
Clown, Fool, or Simply Well Adapted?
• All organisms have evolutionary adaptations
– Inherited characteristics that enhance their
ability to survive and reproduce
• Ex. The blue-footed booby of the
Galápagos Islands has features
that help it succeed in its
environment
• Large, webbed feet help
propel the bird through
water at high speeds, a streamlined shape, large tail,
and nostrils that close are useful for diving, and
specialized salt-secreting glands manage salt intake
while at sea
A Little History…
A Little History…
• Aristotle believed that species are fixed
like rungs on a ladder, life going from
simple to more complex.
• With the study of fossils, things began
to change…
• Mid 1700’s, Georges Buffon suggested
that the earth was very old
Buffon
• Fossils suggested that life forms change
– Evolution was not a new theory
by the early 1800’s, the question
was, “what is the mechanism for
evolution?”
Lamarck
Jean Baptiste Lamarck
• suggested that the best
explanation for fossils and the
diversity of life is that organisms
evolve.
• presented one of the first
theories to give evolution a
mechanism: The Theory of
Acquired Inheritance.
• proposed that by using or not
using its body parts, an
individual tends to develop
certain characteristics which it
passes on to its offspring.
– Ex. The giraffe’s long neck
Charles Darwin
• attended college initially to
become a doctor but did not have
the stomach for it
• went to seminary at Cambridge.
While there, he was intrigued by
the biological and natural
sciences
• decided to take on the job of the
ship’s naturalist on a ship that
was to chart sections of South
American coast line.
• The HMS Beagle’s trip lasted five
years!
• While on the voyage of the HMS Beagle in the
1830s, Charles Darwin observed
– similarities between living and fossil organisms
– the diversity of life on the Galápagos Islands,
such as blue-footed boobies, giant tortoises, and
marine iguanas
Figure 13.1A
• The voyage of the Beagle
Great
Britain
Europe
North
America
Pacific
Ocean
Atlantic
Ocean
Africa
Galápagos
Islands
Equator
South
America
Australia
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
New
Zealand
Figure 13.1B
Darwin gathers background information…
• Darwin became convinced that the
Earth was old and continually
changing
– While on the Beagle, Darwin read Scottish
geologist Charles Lyell’s book entitled
Principles of Geology which argued that
the Earth had changed over time with life
arising, changing and becoming extinct.
– Darwin was also influenced by Thomas
Malthus’ The Principles of Populations
which stated that populations outgrow
their food source and other resources
creating competition. (Leads to famine,
disease, homelessness, war, etc.)
Evolution by means of natural selection.
• Darwin spent 10 years studying his collection from
the Beagle voyage.
• Darwin noticed that many related species differed
in the details and the details were designed for the
region in which they were found. (ex. Finches,
tortoises)
• Darwin developed his theory
that evolution occurs by
natural selection.
Natural Selection
• the process by which individual organisms with
favorable traits are more likely to survive and
reproduce than those with unfavorable traits.
• The genotypes associated with the favored
traits will increase in frequency in the next
generation. Given enough time, this passive
process results in adaptations and speciation
Natural Selection
1. Organisms have a tendency toward
overproduction of offspring. (Think of how
many eggs fish and insects lay!)
2. Individuals show variation in traits.
3. In the “struggle for existence,” favorable
variations are more likely to survive and be
passed on to offspring.
4. Gradually, offspring of survivors make up
larger proportion of population, changing the
population.
Darwin’s Conclusions
– living things also
change, or evolve over
generations
– living species
descended from
earlier life-forms:
descent with
modification
Charles Darwin
British Naturalist
1809 -1882
“I have called this principle, by which
each slight variation, if useful, is
preserved, by the term Natural
Selection.”
—Charles Darwin
from "The Origin of Species"
Darwin publishes his theory
• The Origin of Species
– “There is grandeur in this view of life, with its
several powers, having been originally breathed
into a few forms or into one; and that, whilst
this planet has gone cycling on according to the
fixed law of gravity, from so simple a beginning
endless forms most beautiful and most
wonderful have been, and are being, evolved.”
Another scientist comes to the same conclusion…
Alfred Russel Wallace
"...every species comes into existence coincident in time and space with a preexisting closely allied
species." (1855)
• In 1854 Wallace set out on
a collecting expedition to
the Malay Archipelago.
During his travels he
decided that the
geographical distribution
of species results from
evolutionary forces.
• Wallace deferred to
Darwin and they
corresponded for years.
If there is such a thing as natural selection, is there
such a thing as artificial selection?
• Yes! Artificial selection is the
breeding of certain traits over others.
• Most examples of artificial selection
fall into the category of selective
breeding, in which particular
individuals are selected for breeding
because they possess desired
characteristics or excluded from
breeding because their traits are
undesirable. Both processes have
contributed to the domestication of
animals and plants by humans.
Evidence for Evolution
• Fossil records
• Homologous structures
• Vestigial organs
• Embryological development
• Biochemical comparisons
Comparative
anatomy deals
with the study
of the structure
of animal
bodies.
1. The study of fossils provides strong evidence for
evolution
• Fossils and the fossil record
strongly support the theory of
evolution
– Petrified trees
Hominid skull
Barosaurus
Figure 13.2A, B
– Ammonite casts
– Fossilized organic
matter in a leaf
Figure 13.2C, D
“Ice Man”
Scorpion in amber
Mammoth tusks
Perch
Figure 13.2E, F
• The fossil record shows that
organisms have appeared in a
historical sequence
• Many fossils link
early extinct species
with species living
today
– These fossilized
hind leg bones link
living whales with
their land-dwelling
ancestors
Figure 13.2G, H
2. Homologous structures
Body parts in different
organisms that have
similar bones and
similar arrangements
of muscles, blood
vessels, and nerves
and undergo similar
embryological
development, but do
not necessarily serve
the same function.
Comparative anatomy
Human
Cat
Whale
Bat
Figure 13.3A
Homologous vs. Analogous Structures
• Structures that evolve
separately to perform a
similar function are
analogous. The wings of
birds, bats, and insects,
for example, have
different embryological
origins but are all
designed for flight.
3. Vestigial Structures
• Vestigial structures are anatomical structures of organisms in a
species which are considered to have lost much or all of their
original function through evolution. These structures are typically
in a degenerate, atrophied, or rudimentary condition or form.
Vestigial structures are often referred to as vestigial organs,
though not all of them are actually organs.
• Although the structures most commonly referred to as "vestigial"
tend to be largely or entirely functionless, a vestigial structure need
not necessarily be without use or function for the organism.
Vestigial structures have lost their original main purpose, but they
may retain lesser functionalities, or develop entirely new ones.[1]
Thus, a "vestigial wing" need only be useless for flight to be
vestigial; it may still serve some other purpose than that of a wing.
Examples of Vestigial Structures
4. Embryological
Development
Embryology – the branch of
biology that deals with the
formation, early growth,
and development of living
organisms.
Even before Darwin
proposed the theory of
evolution through natural
selection, Ernst von Baer
claimed that the more
closely related any two
species are, the more similar
their development.
5. Biochemcial Comparisons (protein and
DNA comparisons)
Human
Rhesus monkey
Last common
ancestor lived
26 million years
ago (MYA),
based on
fossil evidence
Mouse
Chicken
Frog
Lamprey
80 MYA
275 MYA
330 MYA
450 MYA
Figure 13.3B
Chromosome Comparisons
- Hominoid Chromosomes
Why so similar?
How can this happen?
Inversion
Meiosis - Tetrads
Crossing Over
Primate Cladogram
Based on Chromosome
changes
VARIATION AND NATURAL SELECTION
Variation is extensive in most populations
• Phenotypic variation may be environmental or
genetic in origin
– But only genetic changes result in evolutionary
adaptation
– How do we get
genetic variation?
How natural selection affects variation
• Natural selection tends to reduce variability in populations
– The diploid condition preserves variation by “hiding”
recessive alleles
– Heterozygote advantage (think of sickle-cell disease).
• Genetic load – the sum total of those alleles that yield some
advantage when they are heterozygous but are lethal or deleterious
when homozygous.
– Some variations may be neutral, providing no apparent
advantage or disadvantage
– Example: human fingerprints
Endangered species often have reduced variation
• Low genetic variability may reduce the capacity
of endangered species to survive as humans
continue to alter the environment
– Studies have shown that cheetah populations
exhibit extreme genetic uniformity
– Thus they may have a
reduced capacity to
adapt to environmental
challenges
Figure 13.17
The perpetuation of genes defines evolutionary
fitness
• An individual’s Darwinian fitness is the
contribution it makes to the gene pool (the
entire collection of genes among a population)
of the next generation relative to the
contribution made by other individuals
• Production of fertile offspring is the only score
that counts in natural selection!
• That is why the male lion will often kill the cubs
when it takes over a new pride! The cubs do not
reflect his genes!
In other words, what adaptations make you more
“appealing” to the opposite gender?
• Sexual selection leads to the evolution of
secondary sexual characteristics
– These may give individuals an advantage in
mating
Figure 13.20A, B
Frequency of
individuals
There are three general outcomes of natural
selection
Original
population
Phenotypes (fur color)
Original
population
Evolved
population
Stabilizing selection
Directional selection
Diversifying selection
Figure 13.19
Modes of Natural Selection
• Stabilizing selection favors the middle
– Ex. Birth weight
• Directional selection favors one of the
extremes, usually due to environment
– Ex. Peppered moth
• Diversifying selection favors the two
extremes
– Ex. Fish in a pond with very light sand and dark
rocks regions.
Natural Selection vs. Evolution
• Natural selection involves the interaction of the
environment and the individual. (Phenotype)
– Natural selection eliminates the less fit, it does
not produce new genotypes and phenotypes!
• Evolution is a change in a population, not the
individual! (Genotype)
• In other words, populations evolve over many
generations as the environment acts on/selects
for the individuals! It is random! No thought
process involved!
Species and Speciation
• Species - a population or group of populations
whose members can interbreed and produce
fertile offspring. (Which type of organism does
not fit this definition?)
• Speciation – the evolution of a new species?
• But how? How can a new species evolve from
an existing species? I’m glad you asked…
The Role of Chance in
Evolution
Genetic drift- random changes in
the allele frequency of a gene pool.
Most likely to occur in small
populations.
Can lead to speciation- the formation
of a new species. Changes
(adaptations) become so severe that
groups can no longer interbreed
successfully.
Maintaining separate species
•
Two different kinds of barriers can prevent
closely related species from interbreeding
1. Prezygotic – prevents mating or fertilization
– 5 types
2. Postzygotic – prevents reproduction of hybrids
– 3 types
Reproductive barriers keep species separate
• Prezygotic and
postzygotic
reproductive
barriers prevent
individuals of
different species
from
interbreeding
Table 14.2
• Courtship ritual in blue-footed boobies is an
example of one kind of prezygotic barrier,
behavioral isolation
• Many plant species have
flower structures that
are adapted to specific
pollinators
– This is an example of
mechanical isolation,
another prezygotic
barrier
Figure 14.2A, B
• Hybrid sterility is one type of postzygotic
barrier
– A horse and a
donkey may
produce a hybrid
offspring, a mule
– Mules are sterile
Figure 14.2C
OK, so that is how a species is “maintained” but
how do we change a species into a new species?
Allopatric Speciation, a.k.a.
Geographic Isolation
Adaptive
Radiation
Sympatric Speciation
It all comes down to
stopping gene exchanges!
MECHANISMS OF SPECIATION
Geographic isolation can lead to speciation
• When a population is cut off from its parent
stock, species evolution may occur
– An isolated population may become genetically
unique as its gene pool is changed by natural
selection, genetic drift, or mutation
– This is called allopatric speciation
Figure 14.3
Geographic isolation can occur in many ways…
• By forming new islands, volcanoes can create
opportunities for organisms (as well as remove
opportunities causing extinctions!)
– Example: Galápagos, Hawaii
– Other examples: the formation of a mountain range, a
shift in a river’s course, glaciers, etc.
Figure 15.4B,
C
• Plate boundaries and earthquake activity can
also create barriers (mountain ranges,
valleys, sea level changes, etc.)
Figure 15.3Ax
Key adaptations may enable species to proliferate
after extreme change.
• Adaptations that have evolved in one
environmental context may be able to perform
new functions when conditions change
– This is called
exaptation.
– Example: Plant
species with
catch basins, an
adaptation to dry
environments
Figure 15.6
Islands are living laboratories of speciation
• On the
Galápagos
Islands,
repeated
isolation and
adaptation
have resulted
in adaptive
radiation of
14 species of
Darwin’s
finches
Figure 14.4A
Adaptive Radiation
a.k.a. divergent
evolution
• The rapid (in
geological terms!)
emergence of new
species from a
common ancestor
introduced to new
and diverse
environments.
• Fills “new”
ecological niches.
• Leads to
biodiversity!
Cactus
ground finch
Medium
ground finch
Large
ground finch
Small
Large cactus
ground finch ground finch
Small
tree finch
Vegetarian
finch
Medium
tree finch
Large
tree finch
Woodpecker
finch
Mangrove
finch
Green
Gray
warbler finch warbler finch
Sharp-beaked
ground finch
Seed
eaters
Cactus flower
eaters
Ground finches
Bud
eaters
Insect
eaters
Tree finches
Warbler finches
Common ancestor from
South America mainland
Figure 15.9
Biodiversity
• The variety of organisms, their genetic information,
and the biological communities in which they live.
• Can be broken down into
– Ecosystem diversity – variety of habitats, living
communities, and ecological process in the living world.
– Species diversity – the vast number of different
organisms on Earth.
– Genetic diversity – the sum total of all the different
forms of genetic information carried by all living
organisms and gives rise to inheritable variation.
Convergent
Evolution
• Species not closely
elated, independently
evolve superficial similarities, because of the
adaptations to a similar environment but do not have a
common developmental origin .
• Structures that are the result of convergent evolution
are called analogous structures
• Ex. The bat’s wing, bird’s wing, and a butterfly’s wing
This can be seen at the biochemical level
too!
• Myosin – a protein found in muscle cells which
reacts with other proteins causing the muscles
to contract, causing movement.
• Yeast have myosin too! Why?
Allows for the movement of
the organelles!
• The original form of myosin made it possible
for parts of the cells to move, the genes evolved
into forms that help our bodies move.
New species can also arise within the same
geographic area as the parent species
• In sympatric speciation, a new species may arise
without geographic isolation
– A failure in meiosis can produce diploid gametes
– Self-fertilization can then produce a polyploid zygote
(3n, 4n, 5n, etc.)
– Most rapid form of speciation! Very common in
plants. Parent species
Zygote
Meiotic
error
Selffertilization
2n = 6
Diploid
Offspring may
be viable and
self-fertile
4n = 12
Tetraploid
Unreduced diploid gametes
Figure 14.5A
Example: Polyploid plants
clothe and feed us
AA
• Many plants
are polyploid
– They are the
products of
hybridization
– The modern
bread wheat
is an example
BB
Wild
Triticum
(14 chromosomes)
Triticum
monococcum
(14 chromosomes)
AB
Sterile hybrid
(14 chromosomes)
Meiotic error and
self-fertilization
AABB
DD
T. turgidum
EMMER WHEAT
(28 chromosomes)
T. tauschii
(wild)
(14 chromosomes)
ABD
Sterile hybrid
Meiotic error and
self-fertilization
AA BB DD
T. aestivum
BREAD WHEAT
(42 chromosomes)
Figure 14.6A
5 Potential Causes of
Microevolution
• Genetic Drift
– Bottleneck effect
– Founder effect
• Gene Flow (ex. emigration,
immigration, etc.)
• Mutation
• Non-random mating (ex. tall women tend to marry
tall men, plants can’t move, island species, etc.)
• Natural Selection or Differential Success
Microevolution vs. Macroevolution
• Microevolution is defined as the change of
allele frequencies (that is, genetic variation
due to processes such as selection, mutation,
genetic drift, or even migration) within a
population.
• Macroevolution is defined as evolutionary
change at the species level or higher, that
is, the formation of new species, new genera,
and so forth.
Evolutionary 'fast-track'
• Evolution has generally been thought of as a
very gradual process
• However, examples of rapid evolution have
been observed
– Antibiotic Resistance
– HIV
• Predator/Prey relationships
can create the right
pressures for rapid
evolution!
"We humans are part of complex
ecosystems, and if we think we're
above the effects of evolution, we're
not looking close enough. If we want
to understand epidemics and
outbreaks of insects such as gypsy
moths, we should not ignore the
effect of evolution.”
T. Yoshiba and R.O. Wayne, Cornell
Univeristy
The evolution of antibiotic resistance in bacteria is
a serious public health concern
(This is also an example of directional selection!)
• The excessive use of antibiotics is leading to the
evolution of antibiotic-resistant bacteria. This is also
happening with fungicide and insecticide resistant
organisms.
– Such evolution only
requires a point
mutation!
– Example:
Mycobacterium
tuberculosis
• One example of rapid evolution occurred
among mosquitoes who migrated into the
London underground
• In less than 150
years, Culex
pipiens evolved
into a new
mosquito species,
Culex molestus
• The origin of new
species is called
speciation
• The isolated mosquitoes adapted to their
new underground environment
– They altered their prey, mating habits, and
breeding patterns
• Environmental barriers that isolate
populations are just one of many
mechanisms in the evolution of species
The tempo of speciation can appear steady or
jumpy
• According to the
gradualist model of
the origin of species
– new species evolve by
the gradual
accumulation of
changes brought about
by natural selection
• However, few gradual
transitions are found in
the fossil record
Figure 14.8A
• The punctuated
equilibrium model
suggests that speciation
occurs in spurts
– Rapid change occurs
when an isolated
population diverges
from the ancestral
stock
– Virtually no change
occurs for the rest of
the species’ existence
Figure 14.8B
EARTH HISTORY AND MACROEVOLUTION
The fossil record chronicles macroevolution
• Macroevolution
consists of the major
changes in the history of
life
– The fossil record
chronicles these
changes, which have
helped to devise the
geologic time scale
Figure 15.1
The actual ages of rocks and fossils mark geologic
time
• The sequence of fossils in rock strata indicates the
relative ages of different species. This is called
relative dating.
• Radiometric (radioisotope) dating can gauge the
actual ages of fossils. The isotopes act as a clock. To
do this, you must ...
– Know the ½ life of the isotope
– Know how much isotope was
originally present
– Know how much of the isotope
is left
Example
•
14C
is the primary isotope used in dating
– When an organism dies, no more C is added
– ½ life of 14C is 5,770 years so all carbon is gone
by 50,000.
• This is a relatively short time compared to how
old the Earth is.
• Option: uranium 235 decays to lead 207, takes
713 million years!
Problems using fossil records…
• Have not found remains of “intermediate” or
transition forms.
– i.e. the missing Link!
• Approx. 2/3 of all the organisms that ever lived were soft
bodied!
• Time averaging – trying to determine the length of
time represented in a given fossil sample by taking
into account the death, burial, and any movement of
remains.
– A bone among clam shells does not have to mean that
they lived in the same time period or even in the same
area!
How do we keep up with all the different
species? (Estimated to be 40 -100
million!)
• Taxonomy (a.k.a. Systematic Biology)
– The field of biology that determines the
classification of an organism based on several
features, such as structure, behavior,
development, DNA, nutritional needs, and
methods of obtaining food.
– Based on evolutionary theory
Why don’t
woodpeckers
get a
headache?
Adaptations
for a
woodpecking
life style…