Bio geographical evidence of evolution, Biology

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BIO GEOGRAPHICAL EVIDENCE-

The patterns of distribution of animals and plants in different parts of the globe are termed as biogeography.
It is believed that around carboniferous period or slightly earlier all the present day continents formed a single large, irregular land mass called Pangaea.
Pangaea splited up and the smaller masses (continents) lighter than the underlying earth crust material gradually floated over it to their present position.
As the continents drifted away, the sea separated them, forming barriers to free intercontinental movements of organisms. Due to different environmental continents, organisms evolved independently in them.
Earlier whole land mass of Globe was one piece called Panagea. 200 - 300 million years ago it got divided as follows -

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Sclater (1858) first divided globe in six zoogeographical regions on the basis of avian fauna.
A.R.Wallace (1876) divided more scientifically on the basis of entire flora and fauna as:

(i) Oriental region	-	Asia (lower China, West Asia, Malaysia, Indonesia, India, Ceylon)
(ii) Australian region	-	Australia, New Zealand, New Guinea, Tasmania, Hawaiian Island.
(iii) Ethiopian region	-	Africa continent, Madagascar, Egypt, Sahara
(iv) Palaearctic region	-	Europe, Most part of China, Japan, USSR, Siberia, N. Sahara
(v) Nearctic region	-	North America continent (USA, Canada, Alaska, Greenland)
(v) Neotropical region	-	South America continent (Mexico, Galapagos island)

Wallace's Line divides Oriental and Australian region.
Darwin (1831) during his expedition on H.M.S. Beagle visited Galapagos Islands (900 Km off West coast of South America) and found many endemic (restricted) species.
He studied 13 different subspecies of finches (Darwin's finches by David Lack 1947) with different eating habits (originally seed-eating).
He reasoned it as suitable adaptation brought by environmental conditions and called the islands as " living laboratory of evolution "
Discontinuous (Allopatric) distribution: When closely related genera are found in different regions.
This indicated that after arising from common stock they were geographically separated and evolved differently.
Due to the geographical barrier they remained isolated and evolved as genera, examples -
Continuous (Sympatric) distribution: When closely related genera are found in the same or connected region. e.g. Prototheria and Metatheria are found only in Australian region.
Sometimes referred as restricted distribution. endemic fauna.

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