Transcript Darwin and Evolution

Evolution
and
Darwin
Evolution
• The processes that have transformed life on
earth from it’s earliest forms to the vast
diversity that characterizes it today.
• A change in the genes!!!!!!!!
Old Theories of Evolution
• Jean Baptiste Lamarck (early 1800’s) proposed:
“The inheritance of acquired characteristics”
• He proposed that by using or not using its body
parts, an individual tends to develop certain
characteristics, which it passes on to its
offspring.
“The Inheritance of Acquired
Characteristics”
• Example:
A giraffe acquired its long neck because its
ancestor stretched higher and higher into the
trees to reach leaves, and that the animal’s
increasingly lengthened neck was passed on
to its offspring.
Charles Darwin
• Influenced by Charles Lyell who published
“Principles of Geology”.
• This publication led Darwin to realize that
natural forces gradually change Earth’s
surface and that the forces of the past are still
operating in modern times.
Charles Darwin
• Darwin set sail on the H.M.S. Beagle (1831-1836) to survey the south
seas (mainly South America and the Galapagos Islands) to collect
plants and animals.
• On the Galapagos Islands, Darwin observed species that lived no
where else in the world.
– Patterns of diversity, e.g., Pinta, Isabela and Hood island tortoises that ate
vegetation, birds (finches) on Galapagos islands
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Far more species than previously known
Similar ecosystems did not have same species
Species adapted to their habitat
Fossils – preserved remains of ancient organism
• These observations led Darwin to write a book.
Charles Darwin
• Wrote in 1859:
“On the Origin of Species
by Means of Natural Selection”
• Two main points:
1. Species were not created in their present
form, but evolved from ancestral species.
2. Proposed a mechanism for evolution:
NATURAL SELECTION
Natural Selection
• Individuals with favorable traits are more
likely to leave more offspring better suited for
their environment.
• Also known as “Differential Reproduction”
• Example:
English peppered moth (Biston betularia)
- light and dark phases
Peppered moths rest on trees and depend
on camouflage for protection.
Evolution by Natural Selection
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Evolution by Natural Selection
– Struggle for existence – competition for resources
– Survival of the fittest (natural selection)– Fitness is
a result of adaptations
• Adaptation – any inherited characteristic that
increases an organism’s chance of survival
• Types of adaptation– Camouflage
– Mimicry – one species resembles another
– Antimicrobial resistance
Darwin’s Beliefs About Descent
• Descent with modification – over long periods
of time, natural selection produces organisms
that have different structures, niches or
occupy different habitats. Each species has
descended with changes from other species
over time.
• Common descent – all living and extinct
species were derived from common
ancestors
Artificial Selection
• Artificial selection – nature provides the
variation, but humans select the variations
they find useful, e.g. breeding the largest
hogs, fastest horses
– The selective breeding of domesticated plants and animals
by man.
• Question:
What’s the ancestor of the domesticated dog?
• Answer: WOLF
Evidence of Evolution
1. Biogeography:
Geographical distribution of species.
Convergent Evolution - similar
environments leads to unrelated species with
similar traits
2. Fossil Record:
Fossils and the order in which they appear
in layers of sedimentary rock (strongest
evidence).
Evidence of Evolution
3. Comparative anatomy
Homologous structures: Structures
that are similar because of
common ancestry
Vestigal structures: traces of homologous
organs in other species
Evidence of Evolution
4. Comparative embryology:
Study of structures that appear during
embryonic development.
5. Molecular biology:
DNA and proteins (amino acids)
6. Experimental evidence
Population Genetics
• The science of genetic change in
population.
Population
• A localized group of individuals belonging
to the same species.
Species
• A group of populations whose individuals
have the potential to interbreed and produce
viable offspring.
Gene Pool
• The total collection of genes in a
population at any one time.
Genetics and Evolution
•
Relative frequency – number of times an allele is present in a gene
pool, compared to the number of times other alleles for the same gene
are present
o EX: Black (B) fur 40% and b fur 60% in mice
o In genetic terms, evolution is the change in relative frequency of alleles in a population
o May not match Mendelian ratios
• Sources of genetic variation
o Mutations – change in sequence of DNA
o Gene shuffling – different combinations of genes during gamete production and crossing
over
• Single gene and polygenic traits
o Natural selection on single gene traits can lead to changes in allele frequencies and thus
evolution (Ex: lizard color, red easy to see and black keeps lizard warmer, reduction in
normal brown which has no advantage)
o Polygenic – Natural selection is more complex and can affect distributions of phenotypes
in 3 modes of action
Modes of Action
• Natural selection has three modes of action:
1. Stabilizing selection
2. Directional selection
3. Diversifying selection
Number
of
Individuals
Small
Large
Size of individuals
1. Stabilizing Selection
• Acts upon extremes and favors the
intermediate.
Number
of
Individuals
Small
Large
Size of individuals
2. Directional Selection
• Favors variants of one extreme.
Number
of
Individuals
Small
Large
Size of individuals
3. Diversifying Selection
• Favors variants of opposite extremes.
Number
of
Individuals
Small
Large
Size of individuals
Hardy-Weinberg Principle
• The concept that the shuffling of genes that
occur during sexual reproduction, by itself,
cannot change the overall genetic makeup
of a population.
Hardy-Weinberg Principle
• This principle will be maintained in nature
only if all five of the following conditions are
met:
1.
2.
3.
4.
5.
Very large population
Isolation from other populations
No net mutations
Random mating
No natural selection
Hardy-Weinberg Principle
• Remember:
If these conditions are met, the
population is at equilibrium.
• This means “No Change” or “No
Evolution”.
Macroevolution
• The origin of taxonomic groups higher
than the species level.
Microevolution
• A change in a population’s gene pool
over a secession of generations.
• Evolutionary changes in species over
relatively brief periods of geological time.
Five Mechanisms of Microevolution
1. Genetic drift:
Change in the gene pool of a small
population due to chance.
• Two examples:
a. Bottleneck effect
b. Founder effect
a. Bottleneck Effect
• Genetic drift (reduction of alleles in a population)
resulting from a disaster that drastically reduces
population size.
• Examples:
1. Earthquakes
2. Volcano’s
b. Founder Effect
• Genetic drift resulting from the colonization
of a new location by a small number of
individuals.
• Results in random change of the gene pool.
• Example:
1. Islands (first Darwin finch)
Five Mechanisms of Microevolution
2. Gene Flow:
The gain or loss of alleles from a
population by the movement of individuals
or gametes.
• Immigration or emigration.
Five Mechanisms of Microevolution
3. Mutation:
Change in an organism’s DNA that
creates a new allele.
4. Non-random mating:
The selection of mates other than
by chance.
5. Natural selection:
Differential reproduction.
Speciation
• The evolution of new species.
Reproductive Barriers
• Any (isolation) mechanism that impedes two
species from producing fertile and/or viable
hybrid offspring.
• Two barriers:
1. Pre-zygotic barriers
2. Post-zygotic barriers
1. Pre-zygotic Barriers
a. Temporal isolation:
Breeding occurs at different times for
different species.
b. Habitat isolation:
Species breed in different habitats.
c. Behavioral isolation:
Little or no sexual attraction between
species.
1. Pre-zygotic Barriers
d. Mechanical isolation:
Structural differences prevent gamete
exchange.
e. Gametic isolation:
Gametes die before uniting with gametes
of other species, or gametes fail to unite.
2. Post-zygotic Barriers
a. Hybrid inviability:
Hybrid zygotes fail to develop or fail to
reach sexual maturity.
b. Hybrid sterility:
Hybrid fails to produce functional gametes.
c. Hybrid breakdown:
Offspring of hybrids are weak or infertile.
Allopatric Speciation
• Induced when the ancestral population
becomes separated by a geographical
barrier.
• Example:
Grand Canyon and ground squirrels
Adaptive Radiation
• Emergence of numerous species from a
common ancestor introduced to new and
diverse environments.
• Example:
Darwin’s Finches
Sympatric Speciation
• Result of a radical change in the genome that
produces a reproductively isolated subpopulation within the parent population (rare).
• Example: Plant evolution - polyploid
A species doubles it’s chromosome # to
become tetraploid.
Parent population
reproductive
sub-population
Interpretations of Speciation
• Two theories:
1. Gradualist Model (Neo-Darwinian):
Slow changes in species overtime.
2. Punctuated Equilibrium:
Evolution occurs in spurts of relatively
rapid change.
Convergent Evolution
• Species from different evolutionary branches
may come to resemble one another if they live in
very similar environments.
• Example:
1. Ostrich (Africa) and Emu (Australia).
2. Sidewinder (Mojave Desert) and
Horned Viper (Middle East Desert)
Coevolution
• Evolutionary change, in which one species
act as a selective force on a second
species, inducing adaptations that in turn act
as selective force on the first species.
• Example:
1. Acacia ants and acacia trees
2. Humming birds and plants with flowers
with long tubes
Fossils
• Fossil - traces and preserved remains of
ancient life, formed in sedimentary rock
• Types of fossils
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Trace - indirect evidence, e.g., footprints
Mold – impression b of an organism
Cast – mold filled with sediment
Replacement – original organism replaced with mineral crystals
Petrified – empty pore spaces filled with minerals, e,g petrified
wood
– Amber – preserved tree sap traps organism
– Original material – mummified or frozen
How Are Fossils Dated?
• Relative dating – age of a fossil is determined
by comparing placement with that of fossils in
other layers of rock
– Index species – compared with other fossils
because they are easily recognized, lived for a
short time and had wide geographic range
• Radioactive dating – use radioactive decay to
assign absolute ages to rocks
– Half life – length of time required for half of the
radioactive atoms in a sample to decay
Early history of life
• Solar system~ 12 billion
years ago (bya)
• Earth~ 4.5 bya
• Life~ 3.5 to 4.0 bya
• Prokaryotes~ 3.5 to 2.0 bya
stromatolites
• Oxygen accumulation~ 2.7
bya photosynthetic
cyanobacteria
• Eukaryotic life~ 2.1 bya
• Muticelluar eukaryotes~ 1.2
bya
• Animal diversity~ 543 mya
• Land colonization~ 500 mya
The Origin of Life
• Old theory of origin of
life – spontaneous
generation (from nonliving)
• Theory of biogenesis
(life from life) – Redi,
Pasteur
Early Atmosphere hydrogen cyanide,
carbon dioxide, carbon
monoxide, nitrogen,
hydrogen sulfide and
water
Early Life
• How did first cells (bacteria) form?
– Protenoid microspheres – large organic
molecules form tiny bubbles
– First life anaerobic, living in the oceans
• Microfossils (microscopic) 3.5 billion years old,
when little oxygen in atmosphere
• By 2.2 billion years, fossil evidence of
microfossils that were photosynthetic
Organic monomers/polymer
synthesis
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Miller/Urey experiment:
Water, hydrogen, methane,
ammonia
No oxygen
All 20 amino acids, nitrogen
bases, & ATP formed
The Endosymbionic Theory
• Mitochondria and chloroplasts were
formerly from small prokaryotes living
within larger cells (Margulis)
Evidence of The Endosymbionic
Theory
• Mitochondria and chloroplasts
– DNA is similar to prokaryotic DNA
– Have their own ribosomes
– Can undergo binary fission