Transcript Early Earth and Evolution

Evolution
Early Earth and Evolution
A THEORY of the origins of the universe
Big Bang
When?
-Approx. 13.5 Billion years ago expansion
from singularity
-MASSIVE AMOUNTS OF ENERGY!
-Energy eventually converted to fundamental
building blocks of matter.
Evidence?
-Expanding universe
-Background radiation
-Abundance of Hydrogen
After Big Bang…….
• Stars!
– Need hydrogen gas fusion
– Form heavier elements
– Really big stars go out with a bang 
supernova!
• Planets!
– Leftover “mess” from supernova start to
accrete into larger objects. (NEWTONS LAW!)
– Typically these objects will orbit around a start
• SOLAR SYSTEMS!
LIFE!!!!
• Spontaneous Generation.
– Theory (hypothesis actually) that life can
randomly emerge from non-living thing
• Biogenesis
– Theory that life only comes from pre-existing
life.
• Common Ancestor
– Theory that every living organism on the
planet is a descendent of an original cell
• Question : Where did first life come
from???
Key Experiments
• Francisco Redi’s Flies –
– Where do maggots come from
– Bottom Line: no spontaneous generation
Key Experiments
• Spallanzani –
– Bacteria in broth come from air? Or other
microbes?
– Bottom Line: no spontaneous generation
Key Experiments
• Louis Pasteur –
– Bacteria in broth come from air? Or other
microbes?
– Key difference from spallanzani?
– Bottom Line: no spontaneous generation
Key Experiments
Stanley Miller –
Can we create
molecules of life
based on conditions
of early earth
Put in inorganic
gasses
Produced organic
amino acids
Questions about the world that started to set the stage for modern
evolutionary thought
• GEOLOGY
– Age of earth?
– Changing earth?
• POPULATIONS
– Competition?
– Change over time?
– Extinction of species?
GEOLOGY
Hutton and Lyell (geologists)
• James Hutton (1785)
– hypothesized earth to be very old when he examined
geologic features such as rock layers and erosion
• Charles Lyell (1833)
– Hypothesized that complex geologic processes like
erosion, volcanoes, etc. shaped the earth as we
currently see it.
• CONCLUSIONS?????
– EARTH IS MAD OLD!
– Today’s best guess???  4.6 Billion Years
How long did this take?????
Early Evolutionists
• Jean-Baptists Lamark (1809)
• Recognized that species change over
time
• VITALISM – 1809
• Change in body structure based
on use/disuse of parts
• Inheritance of acquired
characteristics
• Ex. Early giraffes acquired long necks
through stretching them to reach leaves
in trees.
• Thomas Mathus (1798)
• Observed human population growth will
eventually hit a limit due to living space and
available food. Darwin would later apply this
to all organisms where these limits result in
competition.
• Determined this will reach a max due to food and
space limitations
• Limited resources in Nature is the basis for
what????
• While Lamarck's reasoning behind why
change happened was flawed, Lamarck and
Malthus both greatly influenced the thinking of
Mr. Charles Darwin.
POPULATION GROWTH CURVE
WHERE
ARE
WE???
Charles Darwin
• English scientist born in 1809
• 1831 famous voyage around world on HMS
Beagle where he examined numerous
different types of animals and the wide
diversity of life he found
• Noted that organisms seemed to be
uniquely adapted to their environments
• Galapagos  Similar organisms on different
islands had unique characteristics that
suited their specific habitat
On the Origin of Species
• Published 1859
• Summarized his ideas on causes of
speciation
• Darwin's On the Origin of Species by
Means of Natural Selection, made several
points that had major impact on
nineteenth-century thought:
Darwin and Natural Selection
• Force behind which populations evolve
• Based with the idea that in any given
population, there is a amount of variation
and not a static/fixed existence
• Based on 3 main principles
1) Competition
2) Survival of the Fittest
3) Descent with Modification
1. Competition
• Members of a species population are in
competition with each other for food and
space.
• Due to OVERPRODUCTION
• “Struggle for existence”
• Those individuals with traits that give them
an advantage make them better
competitors.
2. Survival of the Fittest
• Due to the genetic variation in a species, there is
phenotypic variation.
• Due to competition, those organisms that have traits
which give them a slight advantage over others will
survive while those organisms with deleterious traits
will die-off
Fitness: ability to survive and pass on ones genes
• Those with higher fitness pass on more of their
genes to the next generation  Differential
Reproduction
• These “strong” genes then increase in frequency
Golly Gee Mr. Darwin, is survival the only thing needed
to make you “fit”?
No Billy; survival alone is not enough.
An individual who does not
reproduce doesn’t contribute to
his/her population and therefore
doesn’t matter to nature.
3. Descent with Modification
• As new favorable characteristics become
established in a population, the species as a
whole changes as long periods of time pass.
Does evolutionary change happen in an
individual or in a population?
ORIGIN OF SPECIES
• Definition of Species – a group of organisms
that naturally interbreed with each other
• Sometimes, two populations diverge
(change differently) and become two
separate species.
• Ex. Hawaiian Honeycreepers
– All Hawaiian honeycreepers have similarities in
skeletal and muscle structure that indicate they
are closely related.
• Each of the Hawaiian honeycreeper species has a
bill specialized for eating certain foods. Scientists
suggest that all 23 honeycreeper species
apparently arose from a single species that
migrated to Hawaii.
Principle of Common Descent
• All species (living and extinct) have
evolved from common ancestors for a very
long time.
• There is strong quantitative support for this
theory
• The more dissimilar two organisms are,
the further ago their common ancestor
lived.
Evidence of Evolution
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Fossil Record
Geographic Distribution
Transitional Species
Comparative Anatomy
Vestigial Organs
Comparative Embryology
Comparative Biochemistry
Fossil Record
• Preserved remain of ancient
life in sedimentary rock
support change over time.
• Fossils found in lower levels
of rock older than ones
above. (relative age)
• Majority of species (over
99%) that have existed on
this planet are extinct!
• Very hard for an organism
to become a fossil.
How is the age of fossils and rocks
determined?
• Remains of living things are organic – contain
SOME radioactive isotopes of carbon
• Radiometric dating – using half-lives of
radioactive isotopes
– Radioactive isotopes decay at a constant rate
– Half Life  length of time for ½ of an isotope to decay
• Ex. Carbon-14 decays to Nitrogen-14
• Half-life = 5,730 years
• Carbon 14 can only be uses to date fossils less than 50,000 years
old!
Why do we stop taking in carbon 14 when we
die?
A fossil has 1/8th of the atmospheric ratio of C-14
to C-12. Estimate the age of the fossil.
Geographic Distribution
• Biogeography
– study of the distribution of plants and animals
throughout the world
1. Some fossils found on different continents are
nearly identical
- Supports tectonic plate movement
Geographic Distribution
2. Unrelated organisms exposed to same
environmental pressures may develop similar
traits
• ANALOGOUS STRUCTURES
3. Related species have similar physical
anatomy:
– HOMOLOGOUS structures – similar structures, but serve
different functions.
Analogous Structures
• Serve similar function but have a much
different structure
– Ex. Insect wing and bird wing
– Ex. Squid eye and human eye
– Ex. Whale fin and fish fin
Homologous Structures
(Comparative Anatomy)
• Scientists note
similarities among
physiology of
organisms
• Morphologically
similar structures
that perform
different functions
are called
homologous
structures.
Vestigial Organs
• Structures that are of marginal or no use to
an organism NOW
Examples of vestigial structures include:
• Skeletons of some snakes retain the
vestiges of pelvic girdle and leg bones of
walking ancestors.
• Some blind, cave-dwelling fish have eyesockets but no eyes.
Vestigial
• Human
– Appendix
– Tailbone
• Lifestyles change.
– So do we not need the organ and then it gets
modified OR…do organs get mutated so we
find another way to survive.
Comparative Embryology
• closely related organisms go through
similar stages during their embryonic
development
• “ONTOGENY RECAPITULATES
PHYLOGENY!”
Biochemical Similarities
• What we all use
– DNA
– ATP (energy molecule)
– similar enzymes,
– same codons for protein synthesis
– same 20 amino acids etc.
• Remember, at the cell level we are very
close to most other eukaryotic organisms!
Evolution in Action
• All inheritable physical traits that appear in an
organisms can be looked at as changes in an
organism’s genetics
• Darwin did not understand genetics and therefore
could not explain how traits were passed down
through generations.
• We now can apply our understanding of genetics
and apply them to evolutionary theory.
Phylogeny
• the connections between all groups of
organisms as understood by
ancestor/descendant relationships.
• Express relationships using a
CLADOGRAM
Cladogram
• Gene Pool is combined genetic information of
all the members of a particular population
• In a given gene pool, there will typically be two
or more different alleles for a given gene.
• Relative Frequency – number of times that
an allele occurs in a gene pool compared with
the number of times other alleles occur.
• We can oftentimes see that different alleles
have different frequencies in different parts of
the world. Why do you think this is so?
Ex. Frequency of B allele for blood type
Genetic Change basis of Evolution
• Natural selection acts on phenotypes
NOT genotypes, however, this process
determines the relative frequencies of
alleles.
• Ex. Sickle cell anemia
– Phenotype (blood cell shape)  because
heterozygous individuals are resistant to
malaria.
– Malaria resistance causes sickle-cell allele to
be selected for in the population.
Mechanisms of Evolution
• Introduce new Alleles
– Sources of Genetic Variation
• Mutations
• Sexual Reproduction
• External factors affect the allele
frequency
• Remember, it is mutation that proposes
and selection that disposes
Natural Selection  Single Gene Traits
• May result in changes in allele frequencies and
evolution of a population
– Allele which increases fitness of organism becomes
more common
– Allele which decreases fitness of an organisms
becomes less common and may ultimately
disappear altogether.
– Can select for
• Homozygotes  recessive/dominant (Ex. Tay Sachs)
• heterozygote (Ex. Malaria and sickle cell anemia)
Natural Selection Polygenic Traits
• Can affect the distribution of phenotypes in
3 possibly ways
– Directional selection  individuals at one
end of phenotype range have greater fitness
than those in middle or at other end.
– Stabilizing selection  individuals in middle
of phenotype range have greater fitness
– Disruptive selection  Individuals at either
end have greater fitness than those in the
middle.
Directional Selection
• Ex. Pepper Moth (Biston betularia)
• In 1849, a coal-black mutant was found
near Manchester, England. Within a
century, this black form had increased to
90% of the population in this region.
• What was the selection force?
Stabilizing Selection
• Natural selection often works to weed out
individuals at both extremes of a range of
phenotypes resulting in the reproductive
success of those near the mean. In such cases,
the result is to maintain the status quo.
• stabilizing selection is common. In humans, for
example, the incidence of infant mortality is
higher for very heavy as well as for very light
babies.
Disruptive Selection
• In some circumstances, individuals at both extremes
of a range of phenotypes are favored over those in the
middle
• A hypothetical example of this is where you have a
population of rabbits. The color of the rabbits is
governed by two co-dominant traits: black fur
represented by “B” and white fur represented by “W”.
– BB = Black Fur
BW = Gray Fur
WW = White fur
• Put this population of rabbits into an area that had
very dark black rocks as the environment and also
near by was an area of very white colored stone.
– What phenotypes would have the greatest fitness?
• If these populations were to be cut off from each other
thus not being allowed to inter breed it could lead to
Speciation.
What can change allele frequencies
besides natural selection?
• Genetic Drift
– Evolutionary Change can also happen without
natural selection
– In large populations, the laws of probability
help predict allele frequencies.
– In smaller populations random change in
allele frequency (genetic drift) may occur.
– Chance occurrences may increase/decrease
frequency of alleles
Other things that can happen
• Bottleneck – something happens that
leaves only a couple of individuals of a
population alive
• Founder Effect – whoever colonizes new
territory rings only so many alleles
• Migration – new alleles can enter and exit
a population via individuals leaving and
entering.
Genetic Equilibrium
• In order for there to be no evolution (allele
frequencies remain constant) five
conditions must be met;
– Random mating
– Large population
– No migration in or out of population
– No mutations
– No natural selection
• Is this ever the case?
Process of Speciation
• How do new species arise?
• Populations must somehow become
reproductively isolated from each other.
– Behavioral  different behaviors isolate pops.
• Ex. Killer whales may be two different species!
– Geographic  pops. geographically isolated
• Ex. Albert & Kaibib Squirrel
– Temporal  Two pops. reproduce at different times
• Ex. Plants and pollen release
Geographic Isolation
• Often, when geographic barrier is
removed, the two population can no longer
interbreed and now become two species!
Patterns of Evolution
• Macroevolution
– Mass extinction
– Adaptive radiation
– Convergent Evolution
– Coevolution
– Punctuated Equilibrium
Mass Extinction
– Periodic large-scale extinction events
Mass Extinctions
• There have at least 5 mass extinctions.
• Permian – 250 mya, over 90% of marine and
terrestrial species disappeared; maybe due
to volcanoes, Pangeae, glaciation
• Cretaceous – 65 mya; ½ marine and many
terrestrial forms, including dinosaurs; due to
environmental changes or asteroids hitting
the earth
Adaptive Radiation
• Single species evolves into several different
species that live in different ways (adaptations)
Convergent Evolution
• Sometimes nonclosely related
organisms will
evolve similar
characteristics as
each are facing
similar
environmental
pressures.
• Australia has numerous species of
marsupials with only non-Australian
species being the opossum of North
America (how did it get there?)
• Many species of marsupials evolved traits
similar to mammals on other continents
– Ex. Tasmanian Tiger
Co-Evolution
• Due to close relationship two species share with
each other, change in one organism results in a
change with the other.
• BIG TIME EXAMPLE
– FLOWERS AND INSECTS!
TWEEKING DARWINISM
• Traditionally, it was believed that evolution
happened in small steps over long period
of time. This is called gradualism
• More recently, scientists like Stephen Gould,
proposed the idea of punctuated equilibrium
which is that a species may remain relatively
stable with sudden periods of rapid evolution
due to some environmental factor.
– CHANGES IN SPURTS!
GEE WHILIKERS!
IF EVOLUTION IS ONLY A THEORY, CAN’T IT BE
ARGUED THAT IT ISNT SCIENTIFICALLY TRUE?
Theories are nothing to be trifled with.
Remember, it holds a lot of power.
Evolution is an observable fact (bird
beak size changing, antibiotic resistance
in bacteria, etc.) but the term theory
allows it to grow and develop. For
instance, let’s talk about how we have
added to our understanding of evolution
since my time.
HISTORY TIME!
3.5 billion years
First Single-Celled Organism
• Oldest known fossils are stromatolites,
rocklike layers of prokaryotes and
sediment.
Figure 26.3 Early (left) and modern (right) prokaryotes
2.7 billion years ago
Oxygen
Evidence of oxygen accumulation from
cyanobacteria in banded iron
formations
2.1 billion years ago
eukaryotic cells
• Fossils of eukaryotic cells
• Mitochondria and chloroplasts may have
originated as prokaryotes engulfed by
other prokaryotes in endosymbiosis.
• In serial endosymbiosis, mitochondria
probably evolved first
Evidence
• Organelle DNA (similar to bacteria) and
independent protein production
• independent reproduction of organelles
similar to binary fission occurs during cell
mitosis.
• Inner membranes of organelles similar to
that of prokaryotic membranes
1.5 billion years ago
Multicellular organisms
• Oldest known fossils are algae
• Severe ice ages (Snowball Earth)
prevented diversity of eukaryotes for
awhile
535 – 525 Cambrian Explosion
• Great diversity of all types of eukaryotes
500 mya
Movement onto Land
• Evolved adaptations to live on land and
prevent dehydration
• Plants and fungi colonized land together
250 mya
Formation of Pangaea
• Destroyed and altered habitats, changed
climates, created geographic isolation
• http://www.pbs.org/wgbh/evolution/darwin/
origin/
• http://www.micro.utexas.edu/courses/levin/
bio304/evolution/speciation.html