The nebular
hypothesis maintains
that the Solar
System formed from
the gravitational
collapse of a
fragment of a giant
molecular cloud. The
further collapse of
the fragments led to
the formation of
dense cores One of
these collapsing
fragments (known as
the pre-solar nebula)
would form what
became the Solar
System.
The earth was very
hot. The energy from
colliding meteorites
heated the surface of
the earth;
compression of
minerals and from
the decay of
radioactive materials
heated the interior of
the earth.
Volcanoes might
have frequently
spewed lava and
gases – relieving
some pressure in
Earth’s interior.
Gases helped
form Earths early
atmosphere.
Atmosphere
contained no free
oxygen, but
water vapor,
carbon dioxide
and nitrogen.
frequent collisions
with other bodies.
Eventually, the
outer layer of the
planet cooled to
form a solid crust
when water began
accumulating in
the atmosphere.
Around 4.4 billion years
ago earth cooled enough
for water in the
atmosphere to condense
leading to millions of
years of rainstorms with
lightening – enough for
the rain to fill
depressions creating
Earths oceans.
STEP 1
CHEMICAL
EVOLUTION
STEP 2
CO2
H 2O
NH3
CH4
Miller and Urey in 1953
i. Tested the Oparin-Haldane hypothesis by creating
conditions in which there was an
- Atmosphere above warmed sea water that contained H2O,
H2, CH4, and NH3 and
- Electrodes that simulated lightning.
- From this setup, they obtained organic compounds such as
amino acids that were collected in cooled water.
The MillerUrey
experiment
The experiment - organic molecules could be created out of
inorganic molecules.
So…….why don’t we see this happening in today’s world?
Any organic molecules that are now formed would be
used up by living organisms.
If microorganisms were created from these organic
molecules in the early earth’s water bodies, this would have
been an example of spontaneous creation!
For much of history, man believed that living organisms could
be created spontaneously from non-living material (e.g. flies
from dead meat, geese from barnacles, etc.)
This idea was refuted by Louis Pasteur in the 1860’s.
3. RNA was probably the first hereditary material
a. Today, genetic information is usually stored as DNA, but
some organisms such as viruses use RNA to store info.
2 AMINO ACIDS
PROTEIN FORMATION
FORMATION OF NUCLEIC ACID
UNICELLULAR PLANT
MULTICELLULAR PLANT
UNICELLULAR
ANIMAL
MULTICELLULAR
ANIMAL
Mammals
Monocots
Birds
Reptiles
Herbs Shrubs Trees
Dicots
Amphibian
Fish
Flowering plants
Mosses
Insects
Crustacea
Mollusc
Conifers
Ferns
Annelids
Liverworts
Flatworms
Coelenterates
Algae
Fungi
Multicellular
plants
Multicellular
animals
Single celled
organisms
Geologic Time Scale with Key Events
Section 17-3
Era
Cenozoic
Mesozoic
Paleozoic
Precambrian
Time
Period
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Time
(millions of
years ago)
1.8–present
65–1.8
145–65
208–145
245–208
290–245
363–290
410–363
440–410
505–440
544–505
650–544
Key Events
Glaciations; mammals increased; humans
Mammals diversified; grasses
Aquatic reptiles diversified; flowering plants; mass extinction
Dinosaurs diversified; birds
Dinosaurs; small mammals; cone-bearing plants
Reptiles diversified; seed plants; mass extinction
Reptiles; winged insects diversified; coal swamps
Fishes diversified; land vertebrates (primitive amphibians)
Land plants; land animals (arthropods)
Aquatic arthropods; mollusks; vertebrates (jawless fishes)
Marine invertebrates diversified; most animal phyla evolved
Anaerobic, then photosynthetic prokaryotes; eukaryotes,
then multicellular life
Summary of Evolution of Life
Chemical Evolution
(1 billion years)
Formation
of the
earth’s
early
crust and
atmosphere
Small
organic
molecules
form in
the seas
Large
organic
molecules
(biopolymers)
form in
the seas
First
protocells
form in
the seas
Biological Evolution
(3.7 billion years)
Single-cell
prokaryotes
form in
the seas
Single-cell
eukaryotes
form in
the seas
Variety of
multicellular
organisms
form, first
in the seas
and later
on land
EVIDENCES IN FAVOUR OF
ORGANIC EVOLUTION
1. EVIDENCES FROM MORPHOLOGY AND
COMPARATIVE ANATOMY
2. EVIDENCES FROM EMBRYOLOGY
3. EVIDENCES FROM PALEONTOLOGY
EVIDENCES FROM MORPHOLOGY AND
COMPARATIVE ANATOMY
Homologous organs
Organs which have similar structure and embryonic origin but are
different in function are known as homologous organs and the
phenomenon is called homology.
This is due to their common ancestry. Homology is exhibited by
every organ system of vertebrates from lowest to highest including
man.
The limbs of all vertebrates have a common structural plan. For
example forelimbs of variety of vertebrates like whale (flippers), bat
(patagia), birds (wings), horse (legs), man (hands).
The forelimb of man
The forelimb of man, used for handling things
The forelimb of frog
frog which is used for hopping
The forelimb of rabbit
rabbit which is used for leaping
The forelimb of whale
flippers of whale or seal which are used for swimming,
The forelimb of bat
wings of bat and bird used for flying.
Though forelimbs in these vertebrates are modified
for a variety of uses they are constructed on same
fundamental plan.
The pentadactlye plan
The skeleton of forelimb of all the vertebrates
contains humerus, radio-ulna, carpals,
metacarpals and phalanges.
The existence of homologous anatomical organ
structures implies a common evolutionary origin of
amphibians, reptiles, birds and mammals.
Homologies
Anatomical
structures within
Different organisms
Which Originated
from astructure or
Trait of their
Common ancestral
organism.
Analogous organs
Certain organs which perform similar functions but are different in
development and origin are called analogous organs and the
phenomenon is called analogy.
For example the wing of an insect, the wing of a bat and the wing of
bird serve the same purpose of flying but their basic structure is
totally different. The wings of bat and birds are in fact modified forms
of forelegs and internally have the bones, nerves and blood vessels.
While the wings of insects are membranous, made up of thin flap of
chitin and supported by hollow tubes called veins.
Analogous organs show the convergent evolution. This means that
they evolved from different ancestry but developed similar
characteristics when put in similar habitats.
Analogous
Structures
The evolution of
superficially
Similar structures
in unrelated
organisms is
called convergent
evolution.
Vestigial organs
Vestigeal organs are those organs which are rudimentary and nonfunctional in one group of animals while same organs are well
developed and functional in another group of animals.
Presence of vestigial organ is a vital evidence of organic evolution.
From the evolutionary point of view, vestigial organs are structures
that were well- developed, functional and necessary in ancestors
but are now in process of disappearance.
Vestigial Structures
in Man
Vermiform appendix
Nictitating membrane
Coccyx.
Ear muscles
Wisdom teeth
Body hair
EVIDENCE FROM EMBRYOLOGY
Embryology is the science that deals with the study of the development of
embryo. A comparative study of embryology of different groups of animals
reveals certain features which provide evidence for organic evolution.
All multicellular organisms exhibit common pattern of development.
Comparative study of embryological development of different vertebrate like
fish, frog, lizard, chick, rabbit, human etc. shows similarity in early stages.
All vertebrates begin their life history as a single celled zygote.
The zygote in all organisms undergoes series of division to produce
hollow ball of cells called blastula.
Blastula further develops into gastrula.
Gastrula in all the vertebrates has the same three primary germ layers,
namely ectoderm, mesoderm and endoderm.
The young ones of fishes resemble very closely to the tadpole larvae of
amphibians. This shows the origin of amphibians from fish-like
ancestors.
The embryos of all the vertebrates at one stage or the other possess
pharyngeal gill slits,
slits two chambered heart, tail etc. Even human
embryo at eight weeks develops the gill slits and tail. But as the
development proceeds, gill clefts persist only in fishes and get closed in
other vertebrates.
The heart remains two chambered as in adult fish, but it becomes three
chambered in amphibians and most reptiles and four chambered in
crocodiles, birds and mammals.
Comparative Study Of Heart
The fish have a linear heart (sinus venosus, atrium, ventricle and conus arteriosus,
in that order input and output)
The heart of amphibians is modified from the heart of the fish, which was a linear
heart (sinus venosus, atrium, ventricle and conus arteriosus, in that order entry and
exit). The structure of the heart of amphibians is highly variable and has been
modified into a three-chambered heart with two receptacles, and one exit.
In reptiles, changes occurred in the transition environment, an aquatic to land. The
development of this movement involves changes in the structure of the heart to
adapt to new habitats. Reptiles has three chambers, two atria (right and left) and a
ventricle. The ventricle is incompletely subdivided into two chambers.
The circulatory system of birds is composed of a heart and a complex system of
veins and arteries. The major evolutionary advance that arise regarding their
relatives the reptiles is that the heart has four chambers, two atria and two ventricles.
Basically the operation of the mammalian heart is almost the same as birds. Their
hearts are divided into four compartments, two atria and two ventricles.
Comparative Study Of Heart
EVIDENCES FROM PALAEONTOLOGY
Palaeontology deals with the study of fossils.
What are fossils?
Usually plants and animals after death are decomposed by bacteria. But
sometimes they are preserved as fossils.
Fossils are any form of preserved remains or traces, thought to be derived
from living organisms. They provide concrete proof to the fact that variety of
animals and plants had lived in various geological ages of earth.
Examples of fossils
Dinosaurs: They existed on earth some 200 million years ago in the Jurassic
and Triassic periods. The dinosaurs known as Tyrannosaurs were the largest
living carnivore ever. It stood 20ft tall and was about 50 ft in length. It had
dagger like teeth measuring about six inches.
Archaeopteryx: Commonly known as reptile-bird, was a primitive bird-like
form. Its fossil was found in Germany in the rocks of Jurassic period, of about
150 million years ago. It was about the size of a crow and represented both the
characters of birds and reptiles.
Archaeopteryx:
characters of birds and reptiles
 Like birds it had wings with feathers but, wings had clawed digits like
in reptiles.
 It also had beak like in birds. But, beaks had conical teeth like in
reptiles.
 It had feathery tail like in birds. But, Tail was long like lizards and had
tail vertebrae.
 Body was covered with feathers like in birds but also had scales like in
reptiles.
 It skeletal framework resembled more with reptiles than the birds.
 It is probable that it used its forelimb for flying as well as climbing.
Thus,
Archaeopteryx provides a connecting link between reptile and birds.
Evolution of horse:
The history of evolution dates back some 60 m.y.a. in Eocene epoch and
involves about 20 genera. The phylogeny of horse starts with Eohippus, a small
fox like creature with longer head. It had shorter legs with four toes on each front
foot and three on each hind foot. It was a forest dweller, feeding upon soft
vegetations. It passed through evolutionary line to give rise to modern day horse.
Genera
Epoch
1.Eohippus
2.Mesohiuppus
3.Merychippus
4.Pliohippus
5.Equus (modern day horse)
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Major changes seen in modern horse are:
•Enlargement and elongation of third digit
•Loss of other digits
•Elongation of fore part of skull
•Lengthening of limbs
•Increase in the length and mobility of neck
•Development of premolars and molars into high crowned
•Increase in body size
Evolution of horse
The Law of Use and Disuse
• He proposed that if an organ is used a lot
it will develop and strengthen
• If it is not used it will atrophy
• He called this the law of use and disuse
© 2008 Paul Billiet ODWS
The Inheritance of Acquired
Characteristics
• if an organism developed a characteristic feature
through adapting to a new way of life during its
lifetime, it would pass this on to its offspring
• The classic example given is that of the giraffe’s
neck
• As the giraffe’s ancestors searched for a richer
food supply they stretched to reach higher
branches in trees
• Thus their stretched bodies were passed onto
their offspring
© 2008 Paul Billiet ODWS
Natural Selection
• There is variation in all species
• Some variation better adapted for the environment
than others
• Natural selection (survival of the fitter): Individuals
with characteristics better adapted for the
environment will survive and have more viable
offspring than non adapted individuals.
Lamarck’s evidence and inference
• Comparisons
between current
species and fossils:
lines of descendents
• Use and disuse
• Inheritance of
acquired
characteristics
What exactly is a theory?
• Explain which picture describes Lamarck’s
view and which pictures describes Darwin’s
view.
16
claws
wing-like
forelimbs
teeth
thin
ribs
long tail
feathers
Replica of Archaeopteryx fossil;
half bird half reptile
© Alan Richardson
Reptile-like features
Bird-like features
Geologic Time Scale with Key
Section 17-3
Events
Era
Cenozoic
Mesozoic
Paleozoic
Precambrian
Time
Period
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Time
(millions of
years ago)
1.8–present
65–1.8
145–65
208–145
245–208
290–245
363–290
410–363
440–410
505–440
544–505
650–544
Key Events
Glaciations; mammals increased; humans
Mammals diversified; grasses
Aquatic reptiles diversified; flowering plants; mass extinction
Dinosaurs diversified; birds
Dinosaurs; small mammals; cone-bearing plants
Reptiles diversified; seed plants; mass extinction
Reptiles; winged insects diversified; coal swamps
Fishes diversified; land vertebrates (primitive amphibians)
Land plants; land animals (arthropods)
Aquatic arthropods; mollusks; vertebrates (jawless fishes)
Marine invertebrates diversified; most animal phyla evolved
Anaerobic, then photosynthetic prokaryotes; eukaryotes,
then multicellular life