Evolution
Biogenesis
 Biogenesis states all living things come from other
living things.
 Before the seventeenth century it was believed that
living things could arise from nonliving things
 Spontaneous generation
Redi’s Experiment
 Francesco Redi (1626-1697)
 Disproved that flies generated spontaneously from
rotting meat.
 Observed the life cycle of flies.


He noted that maggots appeared where flies had landed, they
turned into pupas and then to flies.
Experiment with open container with rotten meat
(experimental) and closed container with rotten meat
(control).
Spallanzani’s Experiment
 Lazzaro Spallanzani (1729-1799)
 Designed an experiment using a microscope and broth
to disprove spontaneous generation of
microorganisms.
 Not everyone considered is experiment valid. They
believed the heating was not the same for all samples.
 image
Pasteur’s Experiment
 Louis Pasteur (1822-1895)
 The Paris Academy of Science offered a prize to anyone
who could end the spontaneous generation
controversy.
 Pasteur’s experiment won
 Curve-necked flask was used. This allowed for air flow,
but kept out solid particles
 Broth was boiled and let stand

No grow for up to a year
 Neck was broken and growth occurred within a day.
 Spontaneous generation was disproved.
Earth’s History
 Earth is approximately 4.6 billion years old
 Based on studies of Earth’s surface and the use of radiometric
dating.
 First Organic Compounds
 Synthesized from the Earth’s early atmosphere along with a
spark (lighting)
 Cell-Like Structures
 Microspheres-spherical in shape, composed of protein
molecules
 Coacervates-collection of droplets composed of lipids, amino
acids and sugars
 Form spontaneously in the laboratory

Have many of the same properties of life, expect for the hereditary
characteristics.
The First Cells
 It is believed that the first type of cells to evolve where
anaerobic, heterotrophic prokaryotes (anaerobic – live
without oxygen, heterotrophic-consume to get food,
prokaryotes – single cell with no membrane bound
organelles or nucleus
 Feed on the organic molecules from their surrounding
environment
 Eventually these molecules would be gone and the first
autotrophs evolved.
Chemosynthesis
 Autotroph that obtains energy from oxidizing
inorganic compound
 Archea – unicellular organisms that strive in extremely
harsh environments
 Believed to be very similar to the first autrophs to evolve
about 4 million years ago.
 Methanosarcina barkeri

Produces methane during its metabolism
Photosynthetic Autotrophs
 About 3 million years ago the first photosynthetic
organisms evolved.
 Similar to modern cyanobacteria
 Oxygen is a by product of photosynthesis and changed
the make up of the Earth’s atmosphere
The First Eukaryotes
 Features of eukaryotes evolved from prokaryotes
 The ER and nuclear envelope formed from the infolding
of the plasma membrane of a prokaryote
 Lynn Margulis
 Endosymbiosis – eukaryotic cells evolved from a
mutually beneficial relationship between primitive
eukaryote and the prokaryote it engulfed.

Mitochondria and chloroplasts
 Replicate independently and contain some of their own genetic
material similar to prokaryotes
Theory of Evolution
 Charles Darwin (1823-1882) developed his theory
while sailing around the world on the HMS Beagle
 Galapagos Islands
 Evolution – the development of new types of
organisms from preexisting types of organisms over
time; the change in the characteristics of a population
over time
Ideas of Darwin’s Time
 Species were permanent and unchanging
 Jean Baptiste Lamarck (1744-1829)
 Inheritance of acquired characteristics – individuals
could acquire traits during their lifetime as a result of
experience or behavior, then could pass on those traits to
offspring.
Darwin’s Ideas
 On the Origin of Species by Means of Natural Selection
was published in 1859 a year after Darwin presented
his research in London
 His theory was supported by a large amount of evidence
 He used the phrase descent with modification to help
explain evolution
 Species descend by reproduction from preexisting species
 He was the first to argue that all species originate this
way
 Galapagos Finches (Darwin’s Finches)-13 species
Natural Selection
 Natural Selection - Mechanisms of evolution
1. Overproduction of offspring

More offspring are produced than can survive
2. Genetic Variation

Individuals have different traits
3. Struggle to Survive

Competition for resources
4. Differential Reproduction

Organisms with the best adaptation are most likely to
survive and reproduce.
 Survival of the Fittest
Evidence to Support Evolution
The Fossil Record
1.


Types and distribution
of organisms on Earth
have changed over
time.
Fossils of transitional
species show evidence
of descent with
modification
Evidence to Support Evolution
2. Biogeography
 Distribution of organisms, shows evidence of descent
with modification


Animals that are closely related, but adapted to different
environments
Animals that seem unrelated but have similar adaptations to
similar environments
Evidence to Support Evolution
3. Anatomy
Homologous
structures- anatomical
structures that occur
in different species
and that originated by
heredity from a
common ancestor
A.

Similar bone structure of
forelimbs in humans,
penguins, alligators, and
bats
Evidence to Support Evolution
3. Anatomy
B. Analogous Structuresclosely related functions
by do not derive from
the same ancestral
structure

Wings of birds, bats, and
moths

Similar in function, but
not in structure
Evidence to Support Evolution
3. Anatomy
C. Vestigial Structures-serve no function but that
resemble structures with functional roles in related
organisms


Human tailbone(coccyx)- four fused vertebrae that resemble
the bones in an animals tail
Pelvic bones of modern whales and the human appendix
Evidence to Support Evolution
4. Embryology
 Stages of a vertebrate embryo development are very alike

In early development this fades further into development
Evidence to Support Evolution
5. Biological Molecules
 Modern scientists have shown that similarity in subunit
sequences of RNA, DNA, and proteins indicates a
common evolutionary history.

Approximately 98% of our DNA is similar to the DNA of a
chimpanzee.
Evolution in Action
 Evolution is a continuous process and can be observed,
recorded and tested today.
 New species arise from environmental pressure and
interactions with other species including humans.
Convergent Evolution
 Convergent evolution- process by which different
species evolve similar traits.
 They live in similar ecosystems and have similar
pressures.
 Similar but Separate –while they may look similar
their evolution occurred independently of one another.

Bird and bat wings.
Divergent Evolution
 Divergent Evolution- process by which descendants of a
single ancestor diversify into species that fit different
parts of the environment.
 Anole lizards twig-dwelling and trunk-dwelling
 Sometimes, a new population in a new environment,
such as an island, will undergo divergent evolution
until the population fills many parts of the
environment.
 This pattern is known as adaptive radiation
 Darwin’s finches.
Artificial Selection
 Artificial selection – when a human breeder chooses
individuals that will parent the next generation.
 Dogs
Coevolution
 Coevolution – when two or more species have evolved
adaptation to each other’s influence
 Together, but Different
 Acacia tree and acacia ant
Genetic Equilibrium
 Population biologists study many different traits in
populations, such as size and color.
 Traits vary and can be mapped along a bell curve,
which shows that most individuals have average traits,
whereas a few individuals have extreme traits.
 Variation in genotype arise by mutation,
recombination, and the random fusion of gametes.
 The total genetic information available in a population
is called the gene pool
Genetic Equilibrium
 Allele frequencies in the gene pool do not change
unless acted upon by certain forces.
 The principle of Hardy-Weinberg genetic equilibrium
is a theoretical model of population in which no
evolution occurs and the gene pool of the population is
stable
 Genotype frequencies in a population tend to remain
the same from generation to generation unless acted on
by outside influences.
Disruption of Genetic Equilibrium
 Evolution can take place when a population is not in a
state of genetic equilibrium. Thus, evolution may take
place when populations are subject to genetic
mutations, gene flow, genetic drift, nonrandom
mating, or natural selection.
 Emigration and immigration cause gene flow between
populations and can thus affect gene frequencies.
 Genetic drift is a change in allele frequencies due to
random events. Genetic drift operates most strongly
in small populations.
Disruption of Genetic Equilibrium
 Mating in nonrandom whenever individuals may choose
partners. Sexual selection occurs when certain traits
increase an individual’s success at mating. Sexual selection
explains the development of traits that improve
reproductive success but may harm the individual.
 Natural selection can influence evolution in one of three
general patterns.
 Stabilizing selection favors the formation of average traits.
 Disruptive selection favors the extreme traits rather than the
average traits.
 Directional selection favors the formation of more-extreme
traits.
Formation of Species
 According to the biological species concept, a species is
a population of organisms that can successfully
interbreed but cannot breed with other groups. (must
produce fertile offspring)
 Geographic isolation results from the separation of
population subgroups by geographic barriers.
Geographic isolation may lead to allopatric speciation.
 Two closely related squirrels found on opposite sides of
the Grand Canyon.
Formation of Species
 Reproductive isolation results from the separation of
population subgroups by barriers to successful
breeding. Reproductive isolation may lead to
sympatric speciation.
 Competing individuals within a population could gain
an adaptive advantage by using slightly different niches.
Which could lead to the groups becoming
reproductively isolated.

Darwin’s finches.
Formation of Species
 In the gradual model of speciation, species undergo
small changes at a constant rate. In the punctuated
equilibrium model, new species arise abruptly, differ
greatly from their ancestors, and then change little
over long periods.