Evolution

The scanned notes divide evolution into two types:

Types of Evolution

Patterns of Organic Evolution

Page 1 of the supplied notes lists the following five patterns of organic evolution:

1. Divergent evolution (adaptive radiation)
2. Convergent evolution (adaptive convergence)
3. Progressive evolution
4. Retrogressive evolution
5. Parallel evolution

Divergent Evolution

Convergent Evolution

As a result, the organisms have different body organization but possess superficial similarity. The example given in the source is the development of wings in insects, flying birds and mammals.

Evidences of Organic Evolution

Page 2 lists the following evidences of organic evolution:

1. Evidence from morphology, comparative anatomy and vestigial organs
   1. Evidence from analogous organs
   2. Evidence from homologous organs
   3. Evidence from vestigial organs
   4. Evidence from atavism (reversion)
2. Evidence from palaeontology
3. Evidence from embryology
4. Evidence from geographical distribution of animals
5. Evidence from biochemistry and comparative physiology
6. Evidence from genetics

Evidence from Analogous Organs

The example given in the notes is the wings of a butterfly, bird and bat. The wings of these animals perform the same function by assisting in flight, but they differ considerably in their structure.

The source states that this suggests that the organisms might have evolved from dissimilar ancestors.

Evidence from Homologous Organs

The source example is the forelimbs of whale, bat, bird, horse and man. The forelimbs of these organisms perform different functions but are similar in origin.

Evidence from Vestigial Organs

Examples written in the notes include:

The notes state that vestigial organs such as the vermiform appendix suggest that human beings might have evolved from herbivorous ancestors because such organs are functional in herbivorous animals.

Evidence from Atavism (Reversion)

Examples given in the scan include:

Evidence from Palaeontology

The fossil record suggests that evolution has taken place from simple to complex forms in a gradual way of increasing order.

Importance of Palaeontology

• It explains the evolutionary history of organisms.
• It suggests that evolution has taken place from simple to complex forms in a gradual way of increasing order.
• Fossils found in older rocks or deeper parts of rocks are of simpler types, while fossils found in comparatively newer rocks or upper parts of rocks are of more complex organisms.
• Some fossils provide connecting links between two groups of organisms. The source gives Archaeopteryx as a connecting link between birds and reptiles.
• Fossil records indicate that complex forms of life existing today arose from simpler forms of the past.

Archaeopteryx as a Connecting Link

The supplied notes state that Archaeopteryx provides a connecting link between reptiles and birds, suggesting that birds might have evolved from reptiles.

Evidence from Embryology

The source lists three embryological evidences:

1. Similarity in the early development of animals
2. Similarity in vertebrate embryos
3. Recapitulation theory (Biogenetic law)

Recapitulation Theory (Biogenetic Law)

The example given in the scan is the tadpole larva of frog. During the development of frog, a fish-like tailed larva is formed which swims with the tail and respires by gills. The notes state that the tadpole larva resembles an adult fish and is taken as an indication that frogs evolved from fish-like ancestors.