Theories on the Origin of Life
This theory states that life originated on
other Planets outside of our solar system,
and was carried here on a meteorite or
1. Intelligent life seeded the planet.
2. Organic molecules (1st bacterial cells)
formed in space and were carried here by
meteorites or asteroids.
Life was put here, on Earth, by divine forces.
• Because of the separation of church and
state, we are not allowed to teach this in
• This is based on faith not fact.
• Relies on stories that have been passed
down over the years.
Origin from Non-Living
• Life arose from inanimate matter.
Random events produced stable
molecules that would reproduce
themselves. Then Natural Selection
favored changes that increased their
rate of reproduction. This eventually
lead to the first cell. Organic acids
came together to form organisms.
Definition of Evolution
• Evolution is the process of change
• It is the process by which modern
organisms have descended from
• Is the unifying principle for all the
• Provides an explanation for the
differences in structure, function, and
behavior among life forms.
• It includes the change in characteristics of
populations through generations. Thus
existing life forms have evolved from
earlier life forms.
• Comparative Anatomy- this is the comparative
study of certain organisms showing similarities in
• Comparative Embryology- comparison of early
embryonic development among groups of organisms
reveals similarities which suggest common ancestry.
More Supporting Evidence
• Comparative Cytology- Organelles are
structurally and functionally similar in
most divergent organisms, suggesting that
all living things are related to some
• Comparative Biochemistry- Many
different organisms have similar proteins
and enzymes, therefore their DNA must
• Geologic Records- Fossils, the direct or
indirect remains of organisms preserved
in media, suggest links between modern
and ancient forms, as well as, divergent
pathways from common ancestors.
Origins of Life
Early Theories on How
ABIOGENESIS- creation without life.
Spontaneous Generation was the mistaken idea that
life can arise from non-living materials. We
now believe the cell theory. The cell theory
states that all cells come from pre-existing
• Ancient Egyptians believed that eels and frogs
came from the mud of the Nile.
• Aristotle “active principle” responsible for life:
fleas come from sweat
mice come from garbage
flies and maggots come from dead and
• Jan Baptista van Helmont- He was a supporter of the belief
in Spontanous Generation. He experimented with wheat
grains in a sweaty shirt. After 21 days wheat grains are gone
and mice are present. The active ingredient was sweat.
• Francisco Redi- (mid 1600’s) discovered maggots came from
flies not decaying meat. Questioning Spontaneous
• Anton Van Leeowenhoek- Was the first to use a microscope
to see the first living cells. He called the small animals he
observed “animacules”. Took pond water and boiled it. Then
added hay. Organisms were found- hay was the active
• John Needham- (1745) boiled flasks of broth, then sealed
them. Days later microorganisms were found in the broth.
Hypothesized that “animacules” came from the gravy.
• Lorenzo Spallenzini- challenged Needham. Boiled
contents longer, and left one flask open and the
others closed. Life was found in the open flask, and
not in the closed flask. This experiment supported
Redi’s in that it proved life can only come from
• Louis Pasteur- took microorganisms/spores in the air
and used flask with long curved necks to demonstrate
that it was exposure to the air that allowed for the
microorganisms to get into the broth in the flask
This experiment took place over one year. This
finally, and conclusively, disproved Spontaneous
Primitive Life Forms
• Raw Materials- primitive Earth was very hot, consisting of
inorganic substances in liquid, solid, and gaseous states,
having a rich supply of energy.
• Matter- water condensing and falling as rain, carried the
dissolved and atmospheric gases and minerals into the seas,
forming a hot, thin, soup.
• Energy sources- in addition to heat energy in the form of
lightening, solar radiation, and radioactive materials in the
rocks, provided an energy rich environment.
• Energy from the environment contributed to the formation
of chemical bonds among the dissolved particles of the “hot,
thin soup” of the seas.
• What was formed by the chemical bonds?
• This type of synthesis led to the formation of organic
molecules such as simple sugars, amino acids, and nucleic
EARLY THEORIES OF
Theories of Evolution
Jean Baptiste Lamarck- 1809 French Biologist
• Proposed that life evolves or changes.
• Explained evolution as a process of adaptation.
• Law of Use and disuse. -New organs arise
according to the needs of an organism, and their
size is determined by the degree to which they
• Inheritance of acquired characteristics.- Useful
characteristics acquired by an individual during its
lifetime can be passed on to its offspring.
• No evidence to support this theory.
• Helped to disprove Lamarck’s theory
of Inheritance of Acquired Traits.
• Conducted experiments involving the
removal of the tails of mice over
• Found that the offspring of the tail-
less mice did not pass on that
characteristic to their offspring.
• Discovered mutations and proposed that it
was these mutations that were the source
of new traits that permitted evolution to
• This was the one area, in Darwin’s theory,
that was weak. Darwin’s theory did not
account for the genetic basis for
Charles Darwin- 19th century English Naturalist
• Proposed that evolution occurred as the result of Natural
• Overproduction- within a population more offspring are
produced in each generation than can survive, because of
limitations of space and food.
• Competition- individuals compete for the available food and
opportunity to mate and reproduce.
• Variation- within each generation some individuals are better
fitted to survive than others because of variations in
• Survival of the Fittest- those individuals better fitted to
survive are more likely to live long enough to reproduce.
• Transmission of Favorable Traits (Reproduction)- offspring of
the fittest individuals will inherit the favorable variations that
enabled their parents to survive and reproduce.
• Evolution of Species (Speciation)- accumulation of favorable
variations will gradually lead to the appearance of new species
better adapted to their environment.
• Weakness in Darwin’s Theory is that it does not account for
genetic basis of variations. At the time, not much was known
about the mechanisms of genetic inheritance.
• Natural selection is the process where inheritable
traits that make it more likely for an organism to
survive long enough to reproduce, become more
common over successive generations of a
• It is a key mechanism of evolution.
• The Galapagos finches provide an excellent example
of this process. Among the birds that ended up in arid
environments, the ones with beaks better suited for
eating cactus got more food. As a result, they were in
better condition to mate. Similarly, those with beak
shapes that were better suited to getting nectar from
flowers or eating hard seeds in other environments
were at an advantage there. In a very real sense,
nature selected the best adapted varieties to survive
and to reproduce. This process has come to be
known as natural selection.
The Peppered Moth Study
An Example of Natural Selection!
Write similarities and
differences between these two
Both have the Scientific Name:
– Biston betularia
Both are the same moth, commonly called
peppered moths. There is a story behind these
two different color variations. Click to find out
Can you find the • During the early
moth on the tree 1800’s in
England there were
dark and cream
all peppered moths
were cream colored
because the tree
trunks were light
Would it be an advantage or
disadvantage for the moth to be light?
Something was happening in the cities
of England at this time,
What could that have been?
•A greater number of factories were being
created, which meant more pollution!
•What do you think was happening to the
peppered moths as a result of
• Around 1850, black-
moths started to
become more common
than cream, usually in
Why did the frequency of black
moths increase with the growing
Darwin’s Theory of evolution
by natural selection suggests a
White tree trunks were blackened
by heavy pollution from
Which Moth is better adapted to its environment?
•Perhaps dark moths •Light-colored moths
sitting on soot- would have stood out
darkened bark against a dark
escaped being eaten background and
by birds because it would have been
was too hard for the easy prey for hungry
birds to see the dark birds. Therefore,
moths against the more dark moths
dark background. survived.
This is an example of Natural Selection!
• Natural Selection- is a gradual
change in a species in response to
the demands of its environment.
• Write how the peppered moth
during the 1800’s was an example
of natural selection in action!
Background and Observations
• Darwin was born in England, Feb. 12, 1809.
• Studied to become a physician, decided not to continue.
• Studied to become a minister, decided not to continue.
• Graduated college and at the age of 22, signed aboard the
HMS Beagle, as ship’s Naturalist. His job, as naturalist, was
to collect and study plant, animal, and geologic specimens
form the journey around the world.
• The voyage began in December of 1831 and lasted 5 years.
• Darwin kept extensive journals of his observations, studies,
• Darwin’s ideas on gradual change were influenced by the
evidence presented by Charles Lyell. Lyell stated that
gradual and observable geologic processes, such as erosion,
could explain the physical features of the Earth today.
• Darwin was also influenced by James Hutton, who in 1785
proposed that the Earth was formed by geological changes
that occurred over a very long period of time .
• Darwin’s most intriguing finds occurred on the
• After returning home from his voyage, he
continued to wonder about the things that he had
• In 1838, he read an essay by Thomas Malthus, on
human population. Malthus stated in his essay,
that populations can grow much faster than the
rate at which food supplies and other resources
can be produced. Production of more individuals
than the environment can support lead to a
struggle for existence. This concept helped
Darwin to propose a mechanism for evolutionary
• In 1844, Darwin outlined his ideas. In 1858, after
another British naturalist, Alfred Wallace, came to
the same conclusions about the basic mechanism
for evolutionary change, Darwin published his book,
The Origin of the Species by Means of Natural
• There was an enormous number of species that
inhabited the Earth.
• Patterns of Diversity- he asked why similar
ecosystems were inhabited by different types of
species (why the grasslands of England had
rabbits, why the grasslands of Australia had
• Darwin wondered why so many organisms that were
once alive, were now preserved as fossil remains.
Why did these organisms cease to exist? How
were the fossils related to the living organisms?
• The Galapagos Islands- a small group of 16 islands 1000km
off the west coast of Equador. Darwin noticed that even
though the islands were relatively close together, they still
had very different climates.
The lowest were hot, dry, and barren
The highest had more rainfall, vegetation, and
more animal life.
• Darwin noticed that the characteristics of many plants and
animals varied noticeably between the islands.
Hood Island- tortoises had long necks, curved shells
open around the legs, allowing the animal to get more access
to the sparse vegetation.
Isabella Island- tortoises had shorter necks, domed,
curved shell, allowing for the animals to feed better on the
more abundant vegetation that was close to the ground.
• Many specimens of finches were collected and differences
were observed in the shapes and sizes of their beaks.
• After returning to England, Darwin began to wonder if the
animals living on the islands were once members of the same
Supporting Observations For
the Theory of Evolution
• Earth has been estimated to be between 4.5-5 billion
years old. (Determined through radioactive carbon
• Fossil remains-the direct or indirect remains of
organisms preserved in media such as tar, ice, rock, or
• Fossils of prokaryotic life indicate that life existed
over 3.4 billion years ago.
• Fossils can be found in the upper, and lower strata.
These have been found to resemble each other,
suggesting a connection between modern forms and
older forms, as well as, divergent pathways from
• Comparative studies of certain organisms indicate
similarities in anatomical features.
• Homologous structures- anatomical parts that are similar
in structure and origin (development), but function
differently. (Ex.- wing of bird, arm of man, foreleg of
• Homologous bones exist in the forelimbs of many
different vertebrates such as birds, horses, man, bats,
• Analogous structures- are similar in appearance and
function, but have developmental differences. (Ex.- wing
of bird and wing of butterfly).
The study of embryonic developments among groups
of organisms reveals similarities that suggest
1. Early vertebrate embryos resemble each other.
2. As development proceeds, the distinctive
features of each species becomes apparent.
3. All have gill slits, tail-bones (coccyx), segmented
backbones, and are C-shaped.
According to the cell theory, the cell is the unifying
structure for living things. Organelles such as the
cell membrane, ribosomes, and mitochondria, are
structurally and functionally similar in most
divergent organisms. This suggests that all living
things are related to some degree. The fewer the
differences in these cell structures, the closer
the relationship appears.
• Nucleic acids, their structure and
function, are similar in living
• Many different organisms have
similar proteins and enzymes.
• In order for this similarity to
occur, their DNA must be similar.
• The greater their biochemical
similarity, the closer the
relationship among organisms,
thus suggesting evolutionary
• These are structures that do not have
any use, but are the remains of
structures that were once functional in
• Some examples of vestigial organs are:
Humans- appendix, coccyx, 3rd molars
Horses- splint bones
Whales- pelvic (hip) bones
Modern Theory of Evolution
A Time Frame for Evolution
Geographic Isolation- favors speciation
by segregating a small group of
organisms from the main population.
Changes in gene frequency are more
likely to occur in a small population. In
time, this isolated population may
evolve into a separate species due to:
• Different initial gene frequencies than
the main population.
• Different mutations occur within the
main population and the isolated
• Different environmental factors, thus
having different selection pressures
on each population
• An example of this would be Darwin’s
Finches, and Australia’s marsupials,
and the Albert Squirrel.
Reproductive Isolation- separated groups my become
so divergent that even geographic barriers were
removed, interbreeding could not take place. Thus
the populations have become reproductively
isolated and are now two separate species.
• These populations now have separate gene pools.
• Reproductive Isolation results from various
isolating mechanisms that include: Geographic
Isolation, Behavioral Isolation, or Temporal
A Time Frame for Evolution
Gradualism- Gradualism proposes that
evolution is slow , gradual, and continuous.
This viewpoint is supported by geologic
fossils, which show slight changes in
organisms between adjacent layers of
• Species originate through gradual change
of adaptations. There is one line of
Time Frame (cont.)
Punctuated Equilibrium- Punctuated Equilibrium proposes that
species have long periods of stability, interrupted by
geologically brief periods of significant change, during which
a new species may evolve.
• This was proposed by Niles Eldredge, and Stephen Gould in
• Speciation occurs in relatively quickly, in rapid bursts,
followed by long periods of genetic stability in between.
• Environmental changes (higher temps., and introduction of
competitive species) lead to rapid changes in a small
population’s gene pool that is reproductively isolated from
the main population.
• Speciation happens relatively quickly- 10,000 years or less.
• Punctuated Equilibrium involves many lines of descent, it is
a pattern of long, stable periods, interrupted by brief
periods of more rapid change.