Diversity and Unity are the unifying themes of life
Structurally diverse organisms are functionally similar
Unity among organisms is apparent the integral processes of all life
– growth and development, various types of energy procurement,
reproduction, etc.
THE ORIGIN OF LIFE
Diversity and unity are fundamental units of the theory of
Evolution.
Evolution is the plausible explanation for the commonalities and
variations that exist among organisms.

Theories on the ORIGIN OF LIFE
Basic enigma of life: HOW DID LIFE ORIGINATE?
Nothing is directly known about the origin of life, the answer
to this question are exceedingly complex and at best only
tentative.
 Theories of the origin of life: Still a
matter of speculation
 Several intelligent explanations
account for the origin of life on earth

Religion
The origin of life must be attributed to an
agency outside nature called a creator.
Mythology
Philosophy
1.THEORY OF SPECIAL CREATION
support or acceptance mostly
due to faith rather than
experimental or scientific
evidences.
Supporters recently created a
new discipline called “creation
science‖.

 Proposed that universe started from a primeval fireball and had
been expanding and cooling since its inception 10-20 billion years
ago (bya).
 Life originated from outer planets in the form of a resistant spore
(cosmozoa) propelled by radiation pressure, reached earth and
started the first form of life.
Idea was proposed by Richter in
1865. The theory did not gain any
support. Needs evidence for the
existence of ET life.
2. Cosmozoic or Interplanetary
The cosmozoic theory speculates that life
arrived on Earth as bacterial spores,
perhaps enclosed in a comet.

3.ABIOGENESIS (SPONTANEOUS GENERATION)
600 BC up to 2nd half of 19th century – believed that life could arise
spontaneously from nonliving substances.
Living organisms originated in sea lime under the influence of
factors in the environment s.a. heat, air, sun.
Thales (624-548 BC) ---―oceanic
water was the mother from which all
living forms originated‖.
The origin of life without apparent cause

3.ABIOGENESIS (SPONTANEOUS GENERATION)
Aristotle’s Hypothesis
Aristotle (384-322 BC)--- proposed
that living forms are animated forms of
non-living matter.
-Vital forces operate constantly and
improve the living world
Empedocles (540-433 BC) ---―life
originated by itself from non living matter
and imperfect forms were replaced by
perfect forms‖

Biogenesis. Every living thing on earth is the offspring of other living things.
―Life comes from life‖ is referred to as the law of biogenesis, which asserts that
modern organisms do not spontaneously arise in nature from non-life.
Louis Pasteur
Working hypothesis: life arose from pre-existing life
Anton van Leeuwenhoek
Believed that microorganisms arose
from pre-existing organisms.
4. BiogenesisTheory
Francisco Redi
 opposed abiogenesis
proposed that life could arise only
from pre-existing living things (thru
experiment) .
Louis Pasteur was the first to
be able to prove this theory
proposed that the organisms
that are not visible to the
naked eye are present in air.

Broth is boiled. Broth is free of
microorganisms
for a year.
Curved neck
is removed.
Broth is
teeming with
microorganisms
.
Pasteur’s Experiment
demonstrated that fermentation is caused by the growth
of micro-organisms, and that the emergent growth of bacteria in
nutrient broths is not due to spontaneous generation

OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat.
HYPOTHESIS: Flies produce maggots.
PROCEDURE
Controlled Variables: jars,
type of meat, location,
temperature, time
Manipulated Variables:
gauze covering that keeps
flies away from meat
Responding Variable:
whether maggots appear
CONCLUSION: Maggots form only when flies come in contact with meat.
Spontaneous generation of maggots did not occur.
Redi’s Experiment

5. Natural or Marine (Primeval Soup)
 Proposed that life did not originate in the surface of the
earth but deep beneath the sea in or around hydrothermal
vents.
In 1929 by J.B.S. Haldane;
suggested that life was
the result of UV radiation
converting methane,
ammonia and water into
the first organic
compounds in the early
earth oceans.

6. Physico-chemical or coacervate droplet
theory (Oparin and Haldane)
 Chemical evolution:
1. Formation of simple organic compounds
the primitive inorganic molecules of earth interacted and combined
with one another to form simple organic compounds. These were in
the form of simple sugars, fatty acids, glycerol, amino acids and
nitrogen bases.

2. Formation of complex organic compounds
-Simple sugars combined, form complex polysaccharides (starch,
cellulose). Fatty acids and glycerol molecules combined to form
lipids. Amino acids combined forming polypeptides and proteins.
-Purines and pyrimidines combined with simple sugars and phosphates
to form nucleotides, which then formed nucleic acids.
Harold C. Urey and Stanley L. Miller
(1953) – conducted an experiment
simulating the primitive condition of the
Earth.
− discovered that a variety of amino
acids and organic acids were formed

Urey-Miller hypothesis
 Proposed that amino acids can
be synthesized outside living
systems.
 They conducted experiments
in which a gas mixture
containing hydrogen, ammonia,
methane and water vapor was
subjected to electric spark.
 It yielded aldehydes, amino
acids and carboxylic acids.

3. Formation of molecular aggregates (Coacervates):
•Oparin and Fox proposed that the complex organic molecules synthesized
abiotically on the primitive earth formed large spherical aggregates as
cluster of complex organic molecules bound by fatty acids and divide.
•They remained suspended as droplets in sea water
•The coacervates had all the basic properties of living cells like,
metabolism, growth etc.
•However they lacked the complexity of the living cells like organelles.
•Thus these particles with proteins as enzymes and ATP as source of
energy were the first structures at the margin of non-living and living.
4. Formation of first primitive living cell:

Theories on the ORIGIN OF LIFE
Basic enigma of life:
Nothing is directly known about the origin of life, the answer
to this question are exceedingly complex and at best only
tentative.
 Theories of the origin of life: Still a
matter of speculation
 Several intelligent explanations
account for the origin of life on earth
HOW DID LIFE ORIGINATE?

• the earth is about 4.5 billion years old,
• the earliest known cells are found in 3.5 billion year old rocks
• the earliest known eukaryotic cells date to 1.5 billion years
• the earliest multicellular animals date to 650 million years
• the earliest land animals date to about 450 million years
• the earliest mammals date to about 230 million years
• 65 m.y. ago there was a mass extinction of many living things
• the human family tree diverged from the other apes about 4.5 million
years ago

Fossils
 Remains or traces of prehistoric life
 preserved remains of animals, plants or their parts
 Can be of entire organisms or a part which got
buried, a mould or cast, foot prints or imprints on a
stone.

Fossils
• Physical evidence of organisms from the past
• Provides visible evidence that takes us back in time and shows organisms
have changed.
• The fossil record provides incomplete information about the history
of life.
• Paleontologists are scientists who collect and study fossils.
• Over 99% of all species that have lived on Earth have become extinct.
• Where are all these fossils??

Careful study of fossils
Opens a window into the lives of organisms that existed long ago and
provides information about the evolution of life over billions of years
The strata of one location can often be correlated with strata at
another location by the presence of index fossils
Index fossils (also known as guide fossils, indicator fossils or zone
fossils) are fossils used to define and identify geologic periods (or
faunal stages).

 Index fossils. Shelled animals called brachiopods were
extremely abundant in ancient seas. Their fossils are useful
indicators of the relative ages of rock strata in different
locations

Methods of fossilization
Petrifaction- Turn into
stones.
This is due to formation
of sedimentary rocks
under water.
soft parts: disappear;
hard parts: preserved
due to mineralization.
muscles and other
soft organs: get
mineralized and form
rocky fossils.

Preservation of foot prints
 prints, if left undisturbed: hardened and form rocky
fossils.
 such imprints can provide clues regarding the
body form and characteristics of the extinct
animal.
A dinosaur footprint

Preservation in ice
Entire animals can get
frozen and may be
preserved
Body parts remain
intact without change.
 E.g. woolly mammoth
from Siberia

Moulds and cast
 Fossilized moulds are found in volcanic ashes.
 Several invertebrate fossils had been obtained as
moulds.
 provide details about the exact physical features of
the animal.
Natural casts of shelled
invertebrates
Natural mould of a trilobite

 Types of fossils
• Petrified – cavities and
pores are filled with
precipitated mineral
matter
• Formed by replacement –
cell material is removed
and replaced with mineral
matter
• Mold – shell or other
structure is buried and
then dissolved by
underground water
• Cast – hollow space of a
mold is filled with mineral
matter
Fossils: evidence of past life

Fossils: evidence of past life
Types of fossils
• Carbonization – organic
matter becomes a thin
residue of carbon
• Impression – replica of
the fossil's surface
preserved in fine-
grained sediment
• Preservation in amber –
hardened resin of
ancient trees surrounds
an organism

 Trace – aka ichnofossils.
May be impressions made
on the substrate by an
organism. For ex: burrows,
footprints and feeding
marks, and root cavities.
 Coprolites – fossil dung
and stomach contents
 Gastroliths – stomach
stones used to grind food
by some extinct reptiles
Indirect fossil evidence includes:

Dating Fossils
 Relative Dating
-Rock layers form in
order by age—the
oldest on the bottom,
with more recent
layers on top.

Radioactive dating
(Absolute Dating)
 the use of half-lives to determine
the age of a sample.
 A half-life is the length of time
required for half of the radioactive
atoms (C, N) in a sample to decay.
Dating Fossils

 Early members of the animal fossil record
◦ Include the Ediacaran fauna
Important fossils
These animals were the precursors of organisms with
skeletons.

Ichthyostega - interconnecting link
between fishes and amphibians.
Important fossils

Seymouria - Interconnecting link
between Amphibians and Reptiles.
Important fossils

Hyracotherium - Early ancestor of
horses.
Important fossils

Dinosaurs - Extinct group of reptiles.
Important fossils

Archaeopteryx - Ancestral form of birds
Important fossils

Theropods
Allosaurus
Sinornis
Velociraptor
Archaeopteryx
Robin
Light bones
3-toed
foot;
wishbone
Down
feathers
Feathers
with
shaft,
veins,
and barbs
Flight
feathers;
arms as
long
as legs
Important fossils

Rodhocetus, an
ancient whale, lived
about 47 million
years ago.
Rodhocetus ankle bone
(left), a modern
artiodactyl, pronghorn
antelope ankle bone
(right).
Its distinctive ankle
bones point to a
close evolutionary
connection to
artiodactyls.
Important fossils

Dorudonatrox, an ancient whale that lived about
37 million years ago.
Important fossils

Evolutionary significance of fossils
1. Fossils tell us the full story of
evolution. Fossil studies reveal
the course of evolution.
2. Through fossils the origin and
evolution of specific groups of
organisms can be understood e.g.
Horse evolution.
3. Fossils provide us clues regarding
climatic conditions of various
prehistoric periods.
4. Study of fossils simplifies
phylogenetic discussions.
5. Some fossils like woolly
mammoth can provide vital clues
regarding genetic make up.