Transcript Evolution

Evolution
A history of evolutionary thought :
• Linneaus
o Swedish botanist
o Founder of taxonomy
• System of naming and classifying organisms
o Grouped things into categories that would later be
used by Darwin to show relationships
• George Cuvier
o Founded paleontologythe study of fossils
o Understood that extinction
was part of life
o Believed in catastrophismboundaries between layers were due to
catastrophes (flood, drought) and ravaged
regions were populated by migrating species
• James Hutton
o Geologist
o Sought to explain the past by looking at what
currently happens. He said the processes that
formed the earth are still working on it and
observable today
o Believed in gradualism-changes in the earth were
due to slow and continuous processes.
• Charles Lyell
o Geologist, friend to Darwin
o Theory of Uniformitarianism-geologic processes
are so constant that their rates and effects are
balanced over time
• Earth must be very old to allow for these to take place
• Very slow changes that persist over time can produce
substantial changes
• Jean Baptiste de Lamarck
o Published his theory in 1809
o He said evolution is driven by an organism’s
innate desire for perfection
• Lamarck’s incorrect ideas:
1. The Law of Use and Disuse:
• Parts of body used become stronger with use, those not used will
deteriorate
o Most famous example he used was giraffes that had to
stretch their necks to feed gradually became long necked.
2. Inheritance of acquired traitsmodifications acquired in the organism’s lifetime
would be passed on to its offspring.
• Thomas Malthus-mathematician
o Studied populations
o Showed that resources grow linearly but
populations grow geometrically
o Predicted that as the human population
increased we would run out of resources
• Charles Darwin
o Dropped out of medical college
o Had a consuming interest in nature
o Signed on as naturalist on H.M.S. Beagle when 22
yrs. old. The voyage lasted 5 years.
• Galapagos Islands:
• He found species that existed no where else but
were similar to species in S. America
• He recorded 13 species of finches-each has
different beak. Each is adapted to different food
• He realized species change by a gradual
accumulation of adaptations to different
environments.
o A single species of finch was separated by a
channel of water and developed into 2
populations. Each was adapted to its own
environment.
Darwin’s idea of Natural selection:
• There is an unequal ability of individuals to survive
and reproduce
• Variations in traits affect an individual’s ability to get
resources it needs
• The environment will select which traits are the most
fit to survive
• Darwin wrote wrote the Origin of the Species but was
afraid to publish it because of the uproar it would
cause.
• A contemporary, Alfred Wallace, wrote to
Darwin and wanted to publish his own idea of
natural selection.
• Darwin came out with his book the next year and
received credit for evolution as he had more
evidence for it.
• Ideas on evolution in Darwin’s book:
o Descent with modifications-all organisms are
related to each other by descent from an
unknown ancestor in the long ago past
o Over millions of years organisms accumulated
adaptations that served to make them fit for a
specific way of life
o Evolution explains the diversity and unity in life
o Organisms over reproduce (more eggs and sperm
are produced than needed, more offspring made
than will survive)
Evidence for Evolution
I. Geological evidence: fossils
The fossil record shows:
• Prokaryotes are the oldest fossils
• There is a chronological order of appearance in the
vertebrates (fish amphibians reptiles birds
mammals
• Transitional forms link older fossils to newer ones
• Fossil evidence
for evolution in
horses
II. Biogeographic evidence-geographic distribution
of a species
o Modern species are where they are because they evolved from
ancestors that inhabited those same regions.
o Example:
• Sugar gliders and flying squirrels—even though they look alike
and live in similar environments the sugar gliders are related to
marsupials and the squirrel is a placental mammal
III. Comparative anatomy-anatomical similarities
between species in the same categories
1. Homologous structures-same structures but
have different functions.
Example: forelimbs of mammals
2. Analogous structures-have the same function
but are different structures
o Example-bird wing and butterfly wing
3. Vestigial organs-structures of marginal or no use to
an organism
• Whales lack hind limbs but have vestigial bones there, human appendix,
human ear muscles.
• It is not efficient to provide food, oxygen and space to an organ that no
longer has a function
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Third eyelid
Ear muscles
Tailbone
Wisdom teeth
Appendix
IV. Embryological evidence
o Closely related organisms go through similar stages in their embryonic
development
• Gills, tails
V. Molecular biology
o The more closely related 2 organisms are the more alike their biochemistry is
• Shows that all forms of life are related to some extent. Even bacteria and
humans have some proteins in common.
VI. Artificial selection
o Deliberately selecting plants and animals to breed for specific traits produces
changes in the population of that species. Process mimics natural evolution.
Natural selection:
• Darwin’s 5 observations:
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Overproduction of offspring
Populations tend to remain stable in size
Environmental resources are limited
Individuals in a population vary in their characteristics
These characteristics are inherited
• Your fitness is your ability to pass on your genes
• What effects your fitness?
o Your survival
o Your longevity (one mating or several?)
o Early maturity
*You have to consider the whole organism—an
individual may have a weak trait but overall be
more fit to survive than another.
Fitness shows as 3 types of selection:
1. Directional
o Shifts frequency curve in one direction or the other by favoring what
was once rare
• Examples of directional selection:
a. Pepper moths come in 2 forms-black and white
• Industrial areas had trees thick with soot. This made the black moth
more fit to survive. The country had whiter trees. The white moth was
more fit for survival there.
b. Bacterial resistance to antibiotics
• Each time penicillin is used most but not all bacteria are killed.
The survivors have a genetic resistance to penicillin that is
passed on to their offspring. This creates new strains that we
cannot fight.
c. Insect resistance to pesticides (same idea as bacterial resistance)
2. Stabilizing
o Acts against extreme phenotypes, favors the most intermediate individual
o reduces variation
o seen when environments are not changing
3. Disruptive
o Environmental condition vary so that both extremes are favored
Key ideas about Natural Selection:
• It cannot produce perfection. You can only alter
existing structures.
• Adaptations are often compromises (seals move on
land and water but aren’t best adapted for either
• There is an element of chance. When the wind
blows seeds to an island it doesn’t just select the
best seeds
Some types of adaptations
1. Protective coloration
a. camouflage
2. Aposematic coloration
bright colors serve as a warning
example-poison arrow frogs
Nature knows bright colors mean danger
3. Mimicry-one species bears a
resemblance to another species
a. Batesian mimicry-a harmless or palatable species mimics a harmful or
unpalatable
example-monarch and viceroy butterflies
• In order to work, models must outnumber the
mimics
b. Mullerian mimicry-harmful species mimics
another harmful species
examples: insects with yellow and black
stripes
large numbers send the message that this
pattern is bad and to avoid anything with it
4. Deceptive coloration-fake eyes, false heads
5. Symbiotic adaptations-two organisms living
together and/or evolving together
a. Commensalism- (+,0)
One benefits and one is unaffected.
Example-shark and remora.
Shark is not helped or hurt.
The remora gets a free ride and left over food
b. Mutualism- (+,+)
o Relationship is beneficial to both
o Examples-cleaning animals
c. Parasitism (+, -)
o One benefits and the other (host) is harmed
o May live inside or outside host
Causes of Population
Diversity
• Microevolution-small changes that occur from
generation to generation
1. Natural selection-survival of the fittest
• The most favorable traits get passed on
2. Mutations-create new alleles
• They are passed on if they occur in the gametes
3. Mating
• May or may not be random
• Nonrandom mating causes evolution by shifting genotype
frequencies
4. Gene flow-process of gaining or losing alleles in a population
due to migration
• Gene pool-all the genes available in a population
Gene flow
5. Genetic Drift:
• A change in allele frequency in the gene pool due to
chance events. Two situations lead to genetic drift:
a. Founder effect-a few individuals leave to colonize
an isolated place. The smaller the sample, the less
the colonists will represent the gene pool of the
population they left.
Founder effect
b. Bottleneck effect-disasters (earthquakes, floods, fires)
reduce the population
o Who survives is random
o Final population does not resemble the original
Hardy-Weinburg theory
• The frequencies of alleles and genotypes in a
population remain constant from generation to
generation (provided that only Mendelian genetics
are at work)
Conditions for Hardy-Weinberg to work:
1. Must have a large population size
2. They must be isolated from other populations
(no migration)
3. No mutations
4. Mating must be random
5. No natural selection is occurring
The theory tells what to expect when a population
is not evolving.
o These conditions are rarely met in
nature.
o If any are not met, the allele frequency
changes, therefore evolution is
occurring.
H-W equation
Variables:
p = dominant allele
q = recessive allele
p2 = AA genotype or homozygous dominant
q2 = aa genotype or homozygous recessive
2pq = Aa and aA or heterozygous recessi e
Equations:
p2 + 2pq + q2 = 1
p+q=1
Speciation
A species is a distinct group of organisms capable
of interbreeding
o Speciation-evolution of a new species
o Hybridization-interbreeding between species
• Reproductive barriers between species:
1. Prezygotic-prevent fertilization from occurring
a. Ecological isolation-(habitat) 2 groups inhabit the same
area but breed in different parts. Wood frogs breed in
temporary water, bull frogs in larger permanent water
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b. Temporal isolation-reproduce at different time of day, season or
year.
c. Behavioral isolation-courtship behaviors-different species
have different signals-auditory, visual, chemical
http://www.youtube.com/watch?v=o42C6ajjqWg
http://www.youtube.com/watch?v=1Sj-UdjqlFw
d. Mechanical isolation-anatomical
differences-reproductive organs may
not match
e. Gamete isolation-mating may
occur but gametes don’t join due
to differences.
Consider the different types of
fish that release egg and sperm
into water simultaneously.
• Post-zygotic-prevents development of a fertile
offspring even if fertilization occurs
a. Hybrid inviability-genes from parents of different
species do not interact properly for normal
development
b. Hybrid sterility-if an interspecies offspring develops
successfully then it cannot breed (mule)
c. Hybrid breakdown-rare case of interspecies
offspring that mate but F2 will have multiple defects
• If no barriers form between them then mating
may occur creating a new species
What mechanisms are seen that
create a new species?
1. Allopatric speciation-one species is separated by a
physical barrier into 2 or more isolated populations.
2. Sympatric speciation-a new species appears
within the same geographic area where the
original is found.
• Most often occurs by polyploidy where the offspring gets
extra sets of chromosomes (3n or 4n)
3. Adaptive radiation
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Evolution of many diverse species
from a common ancestor when
introduced to a new environment
The speed of speciation-2 ideas:
1. Gradualism-evolution of a new species is gradual
and continuous over long spans of time.
2. Punctuated equilibrium-speciation occurs after a
long period of no change (stasis) followed by rapid
bursts of evolution
Phylogenic relationships
Phylogeny-evolutionary history of a species
Phylogenic treea diagram that shows
probable evolutionary
relationships between
groups
Coevolution:
A change in one species causes a change in
another species
Examples: cuckoo and warbler
(most symbiotic relationships)
Convergent evolution:
two distantly or unrelated organisms come to resemble each
other, usually resulting from similar environments
Classification
• Carl Linneaus
o Swedish Botanist
o developed a system for giving
living things two names
known as Binomial nomenclature
• Each organism is given a genus name and a
species name. Genus represents a small
group of similar organisms, the species
represents all one kind of thing.
• Example:
Acer rubrum
Acer palmatum
Correct method for writing scientific names:
• The genus name is always capitalized, the species is
always small.
• The name then has to be underlined or put in italics.
This sets it apart and makes it recognized as a
scientific name.
• Names are in Latin—meanings won’t change since
it is a dead language.
Classification categories:
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Kingdom
Phylum
Class
Order
Family
Genus
Species
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Human
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animalia
chordata
mammalia
primate
homididae
Homo
sapien
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Housecat
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animalia
chordata
mammalia
carnivora
felididae
Felis
domesticus
Placement today is based on:
1. homologous structures
2. embryos
3. fossils
4. biochemicals
a. DNA
b. RNA
c. Proteins such as cytochrome c
Kingdoms
• Linnaeus started with 2 kingdoms. We now have
6:
1. Eubacteria-”true” bacteria, prokaryotes
2. Archaebacteria-chemistry and structure of cell walls,
lipids and ribosomes is different from other bacteria
3. Protista-eukaryotic cells, may be plantlike, animal like or fungi
like, don’t fit anywhere else.
4. Fungi-eukaryotic, non photosynthetic, cell walls chemically
different from plants
o Plants-multicellular, autotrophic,
cell walls of cellulose
o Animals-multicellular, heterotrophic,
no cell walls