Evolution by Stages

Evolutionary changes are fundamental characteristics of living organisms. Such changes may be convergent or divergent. It means that the similar or dissimilar looking structures may or may not have different ancestral designs. This can be explained by the following examples. 

Eye: Eyes of insects, octopus and vertebrates have similar looks but different structures and must have separate evolutionary origin or different ancestral designs. Rudimentary eye can be useful to some extent.

Feathers: The function of feathers was insulation in cold weather. Later, this feature might become useful for the purpose of flight.

Dinosaurs is an example depicting the presence of feathers in them, but these were not used for flying. Later birds seem to have adaptation of flying using feathers. This shows close relationship of birds to reptiles and proves that characters appearing as a variation can be useful later to perform different functions.

Cabbage: Humans have developed different types of vegetables from the wild cabbage by artificial selection.

Note: Artificial Selection is the selective breeding carried out by humans to alter a population.

The ancestry or phylogeny determined by the comparative study of DNA sequences is called molecular phylogeny. Changes in the DNA during cell division would lead to changes in the proteins that are made from this new DNA and these changes would accumulate from one generation to the next. The organisms which are more distantly related will accumulate a greater number of differences in their DNA.

Evolution should not be equated with 'progress'

Though organic evolution involves descent with modification in which there is a progressive trend of emergence of more or more complex body designs from earlier similar body designs by gradual changes, evolution should not be equated with progress because of following reasons.

1. In evolution, older species are not eliminated during formation of new species and most of the older and simple species still survive. It still continues with its good characters.

Earliest organisms like bacteria are found even in many hospitable habitats like hot springs, deep-sea, thermal vents, Antarctic ice etc. 

2. The evolved species are not always better than the parental species. Evolution depends upon natural selection and genetic drift which together results in a population which is reproductively isolated from the parental species.

1.0Human Evolution

Evolutionary history of man has been built from palaeontology (fossil studies) and molecular biology (especially DNA changes).

Studies have revealed that human evolution started in Africa and the earliest human type was Australopithecus Africans. The African ape man fossil was discovered by Prof. Raymond Dart in which the fossil of skull of  5-6 year old baby from old Pliocene rock of Taung region (S. Africa) was discovered. He named it Taung baby. It had many ape-like characters but had a bipedal locomotion like man. The cradle of human evolution is East Africa where genetic footprints of earliest members of human species Homo sapiens can be traced. A couple of hundred thousand years ago some of our ancestors left across the planet from Africa.

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