Avatar and Dashavatar

The concept of Avataara is a distinguishing feature of Hinduism that is not present in any other religion. God's will is supreme. So, whenever He wants, He can take an Avataara. But, the most important of them all are known as “Dasa Avataara” – the 10 Main Avataaras. He can appear in this world as a concrete person and appear to be in flesh and blood though His body is Suddhasatva. and every such manifestation is called an Avatara
He `touches down' earth so that we can `take off' to his high heavens. He `demotes' himself to our level so as to `promote' us to his level. He `descends' leaving his high pedestal to help us leave our mundane existence and ‘ascend' unto him. He ‘steps down' so that we may ‘step up'. He humbles himself to teach us realize how humble we really are. He manifests himself in `ridiculous' forms like fish, tortoise, boar, half-lion, dwarf etc to appeal to our `ridiculous perceptions' and help us `sublimate' our lives
So, there are- 4 Avataaras in Krita (Matsya, Koorma, Varaaha and Nrisimha)
3 Avataaras in Treta Yuga (Vaamana, Parasuraama and Sri Rama)
2 Avataaras in Dwaapara yuga (Balaraama and Krishna)
1 Avataara in Kaliyuga (the apocalyptic Kalki, yet to be)

Comparision between the theory of evolution and the dashavtara.

First, the creatures that live solely in water(fish) (Matsya);
Then, those that can live in both water and land (amphibian) (Koorma); Then, those that live solely on land (Varaaha);
Then Half-lion and Half-man - a stage between Homo sapiens and animals (Tiryaks) (Nara + Simha);
Then, Homo sapiens with short stature (Vaamana);
Then, the rough and tough and not so civilized human (Parasurama, Rama with the axe)
Then, the Perfect example of Civilized human (Sri Rama, Rama with the bow)
Then, one with occupational (say, Agricultural) skills (Balarama, Rama with the plough)
Then, Superhuman (Sri Krsihna)
Then, the apocalyptic (Kalki)