Dasavatara refers to the ten principal Avatars. In Vaishnava philosophy, an Avatar, most commonly refers to the 'descent' of “God Vishnu” into earthly forms and daśa refers to 'ten' in number. The ten most famous incarnations of Vishnu or sometimes Krishna are collectively known as the Dashavatara. This list is included in the Garuda Purana (1.86.10-11) and denotes those avatars most prominent in terms of their influence on human society. (Wikipedia)

Earlier I was under the impression that all these 10 Avatars refer to the evolutionary way explaining the origin of human form in an evolutionary way, just like the theory of Darwin. In fact the Wikipedia article on Dash avatar mentions this point and compares Darwin's theory evolution with these avatar incarnations. The ten Avatars are in the following sequence Fish, Tortoise, Pig, Lion, Dwarf man, Parasurama (violent man), Rama (Man of peace), Krishna (Man of Philosophy), Buddha (Man of renunciation) and Kalki (Man of Ultimate destruction).Note that this first Avatar is fish and is the most primitive life form and gradually the avatars increase in their consciousness form.

This comparison of Avatar incarnation of animal forms to evolution pathway is wrong. Ancient Hindus never had such an idea. But, in reality they were merely calendar stories explaining the progress of various months throughout the year. These calendar stories follow the Star constellations in ecliptic path way of Sun.

The comparative chart is as given below

 S.No Avatar Star constellations
 1 FishPisces 
Tortoise Antlia

 Pig Monoceros
 4 LionLeo 
 5Dwarf  man Yet to be identified 
 6 Parasurama Gemini/Orion
 7Rama Auriga/Orion 
 8 Krishna Pleiades (Pleiades is associated with peacock--which is the symbol of Murugan as well as Krishna)
9Buddha  Yet to be identified
 10 Kalki (horse) Pegasus

Note that fish is leading all these constellations and gives the effect that as if fish is pulling the boat in which all these animals are present. This leads us the other interesting story.

(Vishnu as fish Avatar pulling the Boat)

According to Hindu mythology

According to the Matsya Purana, the king of pre-ancient Dravida and a devotee of Vishnu, Satyavrata who later was known as Manu was washing his hands in a river when a little fish swam into his hands and pleaded with him to save its life. He put it in a jar, which it soon outgrew. He then moved it to a tank, a river and then finally the ocean but to no avail. The fish then revealed himself to be Vishnu and told him that a deluge would occur within seven days that would destroy all life. Therefore, Satyavrata was instructed to take "all medicinal herbs, all the varieties of seeds, and accompanied by the seven saints” along with the serpent Vasuki and other animals. Lord Matsya is generally represented as a four-armed figure with the upper torso of a man and the lower of a fish. (Wikipedia)

Now, this story will inevitably lead to mother of all stories ---

The story of Ark of Noah.

In the narrative of the Ark, God sees the wickedness of man and is grieved by his creation, resolving to send a great flood to cleanse the Earth. However, he sees that Noah is a man "righteous in his generation," and gives him detailed instructions on how to construct a seaworthy Ark. When Noah and the animals are safe on board, God sends the Flood, which rises until all the mountains are covered and all life on Earth is destroyed. At the height of the flood, the Ark rests on mountaintops, before the waters recede and dry land reappears. Noah, his family, and the animals leave the Ark to repopulate the Earth. (Wikipedia)

The narrative of the Ark has been subject to extensive study by adherents of Judaism, Christianity and Islam, as well as other Abrahamic and non-Abrahamic faiths. Such studies range from hypothetical solutions to practical problems (such as the issues of waste disposal and lighting the Ark's interior), to theological and metaphoric interpretations (with the Ark being seen as the spiritual precursor of the Church in offering salvation to mankind). Although the account of the Ark was traditionally accepted as historical, by the 19th century the growing impact of scientific investigation and biblical interpretation had led most people to abandon a literal view in favour of a more metaphoric understanding. (Wikipedia)

My understanding of this biblical story is that, it had the same origin as Matsya Purana story of India. The place of origin is Mesopotamia, geographically middle place between India and Europe. It is likely that this story could have originated in Mesopotamia and had spread on both directions as well as preserved in both these geographical areas.

Now, the important point for analysis is that is it really story of “Creation Myth” or something else. In my opinion this story is also a calendar story, which explains existence of various animals in heaven and movement of these animals in a heavenly boat. The Stone Age wall paintings also depict these kinds of boat images carrying various anthromorphic forms (Bengt Hemtun). All these animals carried by Noah represent the star constellations. Even now, the same animals are being represented in star constellations.

The problem with mythological stories is that originally they were calendar stories and later moral principles had been added to it to reform the society. This action resulted in preservation of calendar symbolism as well as moral principles. This kind of Chimera stories (calendar stories) have resulted in distortion of philosophical facts and had lead to greater confusion. Hence, it is essential that this kind of distortions should be reduced and eliminated from our religious ideas.