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10/7/2015
EVOLUTION
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CHARLES DARWIN
HMS Beagle in port
Darwin
in 1840
North
America
Great
Britain
Europe
Asia
Africa
PACIFIC
OCEAN
Equator
Galápagos
Islands
Australia
Cape of
Good Hope
Cape Horn
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0
40 km
Tasmania
New
Zealand
40 miles
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THE GALAPAGOS ISLANDS
Many species that live here are found nowhere else in the world
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DARWIN’S THEORY OF EVOLUTION
Living species are different versions of ancestral species
• Published his observation in a book: On the Origin of Species
• Suggested that as descendants of a remote ancestor spread into various habitats (over millions and millions of years) they accumulate diverse modifications.
• Theory: a widely accepted general idea that is broader in scope than a hypothesis 4
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FOSSILS
Fossils document the differences and similarities among present and past organisms
The fossil record –
over millions of years of geological sediment and fossils layered in the order that they appeared in earth’s history
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FOSSILS OF TRANSITIONAL FORMS
Provide evidence for evolution by forming links between ancient and present organisms
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FOSSILS OF TRANSITIONAL FORMS
Provide evidence for evolution by forming links between ancient and present organisms
Pelvis
Femur
Tibia
Foot
Pakicetus
“whale of Pakistan”
Rodhocetus
Dorudon
Living
whales
(cetaceans)
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HOMOLOGOUS STRUCTURES Anatomical similarities resulting from common ancestors
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
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HOMOLOGOUS STRUCTURES Vestigal structures remnants of features that served an important function in an organism’s ancestor Embryo 2
Embryo 1
Pharyngeal
Pouches
(gill like
structures)
Post-anal
tail
Pseudogenes– retained genes that have lost their function
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EVOLUTIONARY TREE Shows patterns of descent and uses homologous structures to indicate where specific characteristics have evolved.
Lungfishes
Branches represent a common ancestor that is
Shared by all species to the right of the branch
Aniotes
Mammals
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Tetrapod
limbs
Lizards
and snakes
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Amnion
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Crocodiles
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Ostriches
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Feathers
Hawks and
other birds
Birds
Hatch marks show
a homologous character
shared by all the groups
to the right of the mark
Tetrapods
Amphibians
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GENETIC VARIATION
Genetic variation in populations is necessary for evolution to occur
• Variation in genotypes that results in different phenotypes
• Pleiotropy (1 gene affects many characteristics) allows for lots of variation Mutations and sexual reproduction produce genetic variation in populations
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EVOLUTION ACTS ON POPULATIONS IT DOES NOT ACT ON INDIVIDUALS
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GENE POOL
All copies of every single allele in all members of a population (Fish tank example)
We can measure evolution by documenting changes in the heritable traits of a population over time (Ex: Fish color)
POPULATION – a group of individuals of the same species that live in the 13
same area and interbreed. (Galapagos tortoises)
EVOLUTION IS A CHANGE IN THE GENE POOL OVER TIME
This can happen several ways:
1. Mutations
2. Non‐random mating
3. Genetic drift (chance events)
‐ bottleneck effect
‐ founder effect
4. Gene flow (migration)
5. Natural Selection
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NATURAL SELECTION Individuals with a certain inherited trait survive better or reproduce more as a result of that trait
Natural selection is the ONLY mechanism that leads to ADAPTATION
EX: Elephant tusks
ADAPTATION – A inherited character that enhances an organisms ability 15
to survive or reproduce in its particular environment
SEXUAL SELECTION
Certain traits increase an organisms fitness by helping them get mates
Male Hercules Beetles fight other males for mates
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SEXUAL SELECTION Sexual dimorphism results in a “showier” sex (often males)
• Female peacocks choose to mate with showy males
• “Good genes” hypothesis
• Can be risky for males!
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NATURAL SELECTION Can affect variation in populations in three ways
1. Stabilizing selection – favors intermediate phenotypes and reduces variation in populations
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2. Directional selection – favors 1 extreme phenotype (common during environmental change or in migrating populations)
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3. Disruptive selection – favors both extreme phenotypes (can result from patchy environments)
3.
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EVOLUTION OF SUPERBUGS By over‐using anti‐biotics we have increased the numbers of drug‐
resistant bacteria or “superbugs”
(Sarcasm)
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Penicillin was the first antibiotic devoped. It is virtually useless today.
BALANCING SELECTION Natural selection can also preserve genetic variation of diploid organisms in a few ways
1. Heterozygote Advantage – selection where heterozygotes have better reproductive success than homozygotes (Ex: Sickle cell anemia)
2. Frequency Dependent – selection that acts against the most common phenotype (Ex: Scale eating fish)
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SELECTION CAN’T MAKE “PERFECT” ORGANISMS Bummer! Why?
1. Selection can only act on existing traits (no traits on demand)
2. Evolution is limited by historical constraints (traits must be passed)
3. Adaptations are often compromises (peacocks)
4. The future is not predictable (environment can change)
Photo courtesy of iflscience.com
Tardigrade: lives in damp environments all over the world
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BUT…BELLA IS PRETTY PERFECT…….
ARTIFICAL SELECTION: selective breeding of plants and animals to promote desired traits in offspring Same idea as natural selection, only WE are doing the selecting instead 22
of the environment
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REQUIRED VIDEOS
Now you know I’m not bluffing about these being on exams!
THE FIVE FINGERS OF EVOLUTION
See link on the course website:
http://www.biosbcc.net/harrer
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