THE ORIGIN OF LIFE
Chapter 14.2
Spontaneous generation
• What does it mean for something to be
spontaneous?
• It used to be thought that living things
could arise from nonliving things.
• If you leave meat outside it will
spontaneously generate flies.
Spontaneous generation
• Francesco Redi – 1668
• He used a cover on one flask, mesh
on another, and no cover on the last
• He found that maggots didn’t appear
on the meat that was covered and free
of flies
Disproving spontaneous Generation
• Pasteur—mid 1800s
• Boiled broth in curved neck flask to
allow air to reach broth but not
microorganisms
• Broth only became cloudy when neck
was broken off.
Biogenesis
• The idea that living things come from
other living things is called biogenesis.
Before life began, two things had to be
true:
• 1) Simple organic molecules must
have formed.
• 2) These molecules must have
become organized into complex
organic molecules (proteins, carbs,
etc.)
Where did the Organic Compounds come
from?
• It’s thought that all of the elements
found in organic compounds were
present on Earth and in the solar
system when Earth formed.
• Alexander Oparin developed a
hypothesis called the primordial soup
hypothesis.
Testing Oparin’s Hypothesis
• Scientists Miller and Urey tested
Oparin’s hypothesis
• were able to produce
organic compounds
including amino acids.
The first cells
• Scientists hypothesis that the first cells
were prokaryotic
• Endosymbiont theory – ancestors of
eukaryotic cells lived in association
with prokaryotic cells.
• Eventually prokaryotes became the
organelles of eukaryotes.
• Mitochondria and Chloroplasts
Endosymbiont theory
• It is widely endorsed but scientists still
do not know the first steps.
What else shows that mitochondria and
chloroplasts may have been their own
organisms?
• They have their own ribosomes.
• They reproduce (by fission)
independently of the cells that they’re
inside.
• Last point, “The evolution of life is
better understood than how the first
life appeared. Fossil, geologic, and
biochemical evidence support many of
the proposed steps in life’s
subsequent evolution.”
HISTORY OF
EVOLUTIONARY
THOUGHT
Chapter 15. 1
History of Evolutionary thought
• In 18th century Europe, it was believed
that life had never changed in the few
thousand years that life had existed on
Earth.
• However, scientists began studying
rock layers (strata) and learned more
about geology and living things of the
past.
Influential Scientists
• Cuvier’s Discoveries
• Some past organisms differ greatly
from living species
• Some organisms became extinct
• BIG IDEA: Geology and life had
changed
Influential Scientists
• Lyell’s Idea – Uniformitarianism
• Geologic processes that have
changed the shape of the Earth’s
surface in the past continue to work in
the same ways.
Influential Scientists
• Jean Baptiste Lamarck’s Ideas
• Simple life forms develop into more
complex forms
• Individuals can acquire traits during
their lifetime and pass on those traits
to their offspring (inheritance of
acquired characteristics)
What does “Inheritance of Acquired
Characteristics” Mean?
• Example: A population of giraffes all had
short necks and were able to reach their
food. However, when they were forced to
move to an area with taller trees, they could
no longer reach their food. So they
stretched and stretched until they could
reach. Then when Mr. & Mrs. Giraffe had
babies, their babies had long necks
because their parents had acquired long
necks.
In other words…
• The changing environment changes a
need and the modification results from
that need.
Charles Darwin
• Darwin sailed around the world on the H.M.S.
Beagle and became the ship’s naturalist.
• He made observations, kept journals, and
collected bones and specimens.
• He knew about Selective Breeding/Artificial
Selection: production of offspring with desired
traits
• He observed that a number of fossil organisms
he found were very similar to living organisms.
• He observed that similar organisms existed in
very different locations.
Darwin’s Ideas
• He described evolution with the phrase
“descent with modification,”
• meaning that all species descended from
preexisting species but changed over time.
• For example, there are 13 species of
finches on the Galapagos Islands, each
containing a beak that is best adapted to a
certain type of food.
• He believed that they all descended from a
common ancestor.
Darwin’s Finches
Descent with modification
• Darwin proposed natural selection as
the mechanism for descent with
modification.
Requirements for natural selection
1. Overproduction – More offspring
produced than can survive
2. Genetic Variation—Individuals in a
population have different traits,
mostly inherited, sometimes new
Requirements for natural selection
Heritability- Variations are inherited
from parents (like produces like)
4. Reproductive Advantage—
Individuals that have certain traits
are more likely to survive and
reproduce than are individuals that
lack those traits.
Over time, those traits become
more frequent in the population.
3.
Struggle to survive
• Individuals must compete for limited
resources, avoid predators, disease,
and unfavorable conditions
• A trait that makes an individual
successful in its environment is an
adaptation.
Survival of the Fittest
• Fitness refers to one’s ability to
survive to maturity and reproduce.
• If a certain trait increases one’s
fitness, it will likely increase in the
population. These are adaptations
(e.g. speed, agility).
The Origin of Species
• Darwin Published the book The Origin
of Species from all of his observations
and data collection on his voyage.
• Defined EVOLUTION: cumulative
changes in groups of organisms
through time.
• Natural selection is the way in which
evolution occurs.
EVIDENCE OF
EVOLUTION
Chapter 15.2
Support for evolution
• The Theory of
Evolution
suggests that all
organisms on
Earth have
descended from a
common
ancestor.
Support for evolution: The fossil record
• The fossil record is an important source of
information for determining the ancestry of
organisms and patterns of evolution.
• We can see that species have differed in a
gradual sequence of forms over time,
• transitional species have features
intermediate between those of
hypothesized ancestors and later
descendent species.
Support for evolution: The fossil record
• Two major classes of traits used when
studying transitional fossils:
• Derived traits- newly evolved features
• Ancestral traits- more primitive
features
Support for evolution: comparative anatomy
• How does the anatomy of one animal
compare to another?
• Homologous Structures- anatomically
similar structures inherited from a
common ancestor.
Support for evolution: comparative anatomy
• Evolution predicts that organism's body
parts are more likely to be modifications of
ancestral body parts than they are likely to
be entirely new features.
• This is not proof… But an example for
which evolution is the best available
explanation for this biological data.
Support for evolution: comparative anatomy
• Analogous Structures- structures that have
the same function but different construction
• NOT inherited from a common ancestor.
• Not all anatomically similar features are
evidence of a common ancestor.
Support for evolution: comparative anatomy
• Vestigial structures- a functioning structure in
one species is smaller or less functional in a
closely related species.
• Evolutionary theory predicts that features of
ancestors that no longer have function will
become smaller over time until they are lost.
Support for evolution: comparative embryology
• Embryo- organisms early prebirth stage of
development.
• Embryos exhibit homologous structures
during certain phases of development but
become totally different
structures in adult forms
Support for evolution: comparative
biochemistry
• Evolutionary theory predicts that molecules in
species with a recent common ancestor should
share certain ancient amino acid sequences.
• The more closely related the species are the
greater number of sequences that will be
shared.
• The fact that many organisms have the same
complex molecules suggests that these
molecules evolved early in the history of life and
were passed on through life forms that have
lived on Earth.
Support for evolution: geographic distribution
• Biogeography- study of distribution of
plants and animals on Earth.
• Example: Why do islands have more
plant diversity than animal diversity?
The plants are more able to migrate
from the closest mainland as seeds,
either by wind or on the backs of birds.
Adaptation
• An adaptation is a trait shaped by natural
selection that increases an organism's
fitness (reproductive success).
• Fitness- a measure of the relative
contribution that an individual trait makes
to the next generation (measured by the
number of reproductively viable offspring
that an organism produces in the next
generation).
Types of Adaptation
• Camouflage- allows organisms to become
almost invisible to predators.
• Mimicry- one species evolves to resemble
another species.
• Antibiotic Resistance: bacteria developing
drug resistances to certain antibiotics
SHAPING
EVOLUTIONARY
THEORY
Chapter 15.3
Hardy Weinberg equilibrium
• Equilibrium means not evolution is
occurring.
• the population must meet 5 conditions
• 1. no genetic drift
• 2. no gene flow
• 3. no mutation
• 4. mating must be random
• 5. no natural selection
Hardy Weinberg equilibrium
• populations in nature might meet
some of these requirements,
• but hardly any population meets all 5
conditions for long periods of time.
Mechanisms of Evolution: genetic drift
• What’s an allele again? It’s an alternative form
that a single gene may have for a particular
trait.
• Any change in the allelic frequencies (# of
each kind of allele in the population) that
results from chance.
• These effects are more pronounced in smaller
populations.
Mechanisms of Evolution: genetic drift
• Founder Effect- small sample of a
population settles in a location separated
from the rest of the population.
• Alleles that were uncommon in the
original population might become
common in the new population
• Bottleneck- population declines to a very
low number then rebounds.
Mechanisms of Evolution:
Gene Flow
• Can occur during migration of individuals from
one population to another
• When the migrating individuals breed with the
new population, they contribute their genes to
the gene pool of the local population
• Makes gene pools of the same species more
similar to one another
• Ex: wind carrying seeds from parent
population to another population
Mechanisms of Evolution:
Nonrandom Mating
• What would completely random mating look like?
• Potential mates have an equal chance of
being selected.
• The result of nonrandom mating is that some
individuals have more opportunity to mate than
others and thus produce more offspring
• It is simply easier to mate with a nearby
individual, as opposed to one that is farther away.
• individuals compete for mates and active
selection of mating partners occurs.
Mechanisms of Evolution: Mutation
• Mutation, a driving force of evolution, is a
random change in an organism’s genetic
makeup, which influences the population’s
gene pool.
• Mutations give rise to new alleles;
therefore, they are a source of genetic
variation in a population.
• Mutations may be harmful or benign, but
they may also be beneficial.
Mechanisms of Evolution:
Natural Selection
• Individuals in a population are not equally
adapted to the environment
• Best traits for that environment survive
Mechanisms of Evolution:
Natural Selection
• Directional: an extreme version of a trait makes
an organism more fit
• Stabilizing: elimination of
extreme traits
• Disruptive: elimination
of the average trait,
retention of the
2 extremes
speciation
• For speciation to occur, a population
must diverge and then be
reproductively isolated.
• Allopatric Speciation: a physical barrier
divided one population into two
• Sympatric Speciation: a species
evolves into new
species without a
physical barrier
Prezygotic Isolating Mechanism
• Prevent genotypes from entering a
population’s gene pool through
geographic, ecological, behavioral, or
other differences that happen BEFORE
fertilization
Postzygotic isolating Mechanism
• Operate AFTER fertilization ensuring
hybrids are infertile (cannot reproduce)
and thus cannot pass on their genes
Rate of speciation
• Gradualism: evolution
proceeds in small,
gradual steps
• Punctuated
equilibrium: rapid
spurts of genetic
change cause
species to diverge
quickly
Patterns of Evolution
• (A) Divergent Evolution (a.k.a. adaptive
radiation)
• One ancestral species evolves into a
number of different species, sharing a
common ancestor.
• Ex. Darwin’s finches
Patterns of Evolution
• (B) Convergent Evolution
• Unrelated species evolve similar traits
even though they live in different parts of
the world
Patterns of Evolution
• Co-Evolution
• Different species become more similar
due to similar environments
• Ex. Mutualism of comet orchids and
moths that pollinate them
Mechanisms Video: 5 Fingers of
Evolution
• http://ed.ted.com/lessons/five-fingers-of-evolution#watch
Pinky- Shrinking Population (aka genetic drift- which is more pronounced in a
smaller population- founder effect & bottleneck
Ring- Nonrandom Mating
Middle- Mutation
Pointer- Gene Flow
Thumb (up/down)- natural selection