Evidences of Evolution - notes
Origin of Life:
Evolution can explain formation of many species ultimately from a single
species in the past. But origin of life (first species) needs further explanation.
Oparin and Haldane proposed biochemical theory of evolution:
Chemical evolution: Formation of simple organic substances (amino acids,
glucose, nucleotides) from inorganic substances CH4, NH3, H2S on
primitive Earth.
Biological/ Organic Evolution: Formation of first primitive cell using organic
molecules. Evolution of different forms of life forms from simple unicellular
prokaryotic organism
Miller and Urey experiment: They simulated primitive earth.
Primitive reducing atmosphere Gases like H2S, NH3, CH4
Evaporation from hot oceans Boiling water in flask
Lightening Electrodes
Rainfall Condensation using cold water
They showed formation of simple substances in water taken in experimental
set up and confirmed Harold and Urey’s theory.
Evolution and classification
Both evolution and classification are interlinked.
1. Classification of species is reflection of their evolutionary relationship.
2. The more characteristic two species have in common the more closely
they are related (and will be placed in same group during classification).
3. The more closely they are related, the more recently they have a common
ancestor.
4. Similarities among organisms allow us to group them together and to
study their characteristic.
TRACING EVOLUTIONARY RELATIONSHIPS
(Evidences of Evolution)
I.Morphological and anatomical evidences. External and internal structures
are compared to find out evolutionary relationships.
A.Homologous Organs : These are the organs that have same basic structural
plan and origin but different functions.
Homologous organs provides evidence for evolution by telling us that
they are derived from the same ancestor. (Divergent Evolution)
Examples :
Organs Function
Forelimb of Horse (Running)
Wings of bat (flying)
Paw of a cat (walk/scratch/attack)
Example from plants
Tendrils in cucurbits (climbing/support)
Thorns in bougainvillea (protection)
(both are stem modifications)
Tendrils in pea plant (climbing support)
Spines of cactus (protection)
(both are leaf modifications)
Tendrils in pea plant (climbing support)
Spines of cactus (protection)
(both are leaf modifications)
B. Analogous Organs : These are the organs that have different origin
and structural plan but perform same function.
Analogous organs indicate towards Convergent Evolution i.e. structures derived
from different ancestors adapt to perform same function.
Example : Organs Function
Wings of bat ® elongated fingers
with skin folds Flying
Wings of bird ® Feathery covering
along the arm
Example from plants
Spines in Cactus (modified leaf)
Thorns in Bouganvilea (modified stem) Protection
II. Fossils : (Palaeontological evidences)
Fossils are preserved body parts or traces of living organisms of the past.
ü To study and compare structural features of extinct organisms in order to
find evolutionary relationship, we study fossils.
ü Fossil Archeaopteryx possess features of reptiles as well as birds. This
suggests that birds have evolved from reptiles.
Examples of Fossils
AMMONITE - Fossil-invertebrate
TRILOBITE - Fossil-invertebrate
KNIGHTIA - Fossil-fish
RAJASAURUS - Fossil dinosaur skull
Determining age of fossils:
I. Deeper the fossil, older it is.
1. ...........................
2. ...........................
Recent 3. ...........................
4. ...........................
5. ..........................
6. .......................... Older
II. Detecting the ratios of different isotopes of the same element in the
Fossil material i.e. Radio-carbon dating (C-14 dating)
III. Molecular Phylogeny (Molecular Evidence)
It is based on the idea that changes in DNA during reproduction are the
basic events in evolution
Organisms which are more distantly related will accumulate greater
differences in their DNA than closely related organisms.
So we look for differences in DNA to find out evolutionary relationships.
Evolution of New organs/ structures
Evolution takes place in stages i.e. bit by bit over generations.
A. Usefulness/Fitness advantage in Intermediate stages.
Evolution of Eyes
Evolution of complex organs is not sudden it occurs due to minor
changes in DNA, however takes place bit by bit over generations.
Flat worm has rudimentary eyes
Insects have compound eyes
Humans have binocular eyes
But these eyes have differnces in structure and hence have different
ancestoral origin.
B.Preadaptation/ Functional Advantage of Intermediate stages.
Evolutions of feathers
Feathers ® provide insulation in cold weather but later they might
become useful for flight.
Example : Dinosaurs had feathers, but could not fly using feathers.
Birds seem to have later adapted the feathers to flight.
Evolution by Artificial Selection : Humans have been a powerful
agent in modifying wild species to suit their own requirement through
out ages by using artificial selection. eg (i) From wild cabbage many
varieties like broccoli, cauliflower, red cabbage, kale, cabbage and
kohlrabi were obtained by artificial selection. (ii) Wheat (many varieties
obtained due to artificial selection).
Wild cabbage:
Broccoli: Arrested flower development
Cauliflower: Has sterile flowers
Cabbage:With short distance between the leaves
Kale: With larger leaves
Kohlrabi: With swollen parts
Evolution: Ladder vs Tree
Evolution can not be equated with progress (ladder) but aims at producing
more diversity (Tree).
HUMAN EVOLUTION
Although there is great diversity of human forms all over the world yet
all humans are a single species.
GENETIC FOOTPRINTS OF HUMANS
Hundreds/thousand of years ago Earliest members arose in Africa.
They migrated to many places namely East Asia, South Africa, Philippines,
Island of Indonesia, West Asia, Central Asia, Australia, Eurasia.
They did not go in a single line
They went forward and backward
Moved in and out of Africa
Sometimes came back to mix with each other.
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