Notes- Evidences of Evolution (Heredity and Evolution)

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 pea plant                 (climbing/support)

Thorns in bougainvillea                  (protection)

(both are stem 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.