It's also suggested by some Vedic scholars that the avatars of Vishnu like Fish, Tortoise, Boar, half-man-lion, dwarf etc suggest evolution of life on earth, suggesting also that all life-forms are divine descendants. An excerpt from Wiki
The ten best known avatars of Vishnu are collectively known as the Dasavatara (a dvigucompound meaning "ten avatars"). This list is included in the Garuda Purana (1.86.10"11).The first four are said to have appeared in the Satya Yuga (the first of the four Yugas or ages in the time cycle described within Hinduism). The next three avatars appeared in the Treta Yuga, the eighth descent in the Dvapara Yuga and the ninth in the Kali Yuga. The tenth, Kalki, is predicted to appear at the end of the Kali Yuga.Matsya, the fish-avatar who saved Manu – the progeniter of mankind from the great deluge and rescued the Vedic scriptures by killing a demon. Story can be found in the Matsya Purana.Kurma, the tortoise-avatar, who helped in the Samudra manthan – the churning of the ocean. Story can be found in the Kurma Purana.Varaha, the boar-avatar, who rescued the earth from the ocean, by killing her kidnapper-demon Hiranyaksha. Story can be found in the Varaha Purana.Narasimha, the half man-half lion avatar, who killed the tyrant demon-king Hiranyakashipu, to rescue the demon's son Prahlada, who was a Vishnu-devoteeVamana, the dwarf-avatar, who subdued the king Maha Bali. Story can be found in the Vamana Purana.Parashurama, sage with the axe who killed the thousand-armed king Kartavirya ArjunaRama, the king of Ayodhya and the hero of the Hindu epic RamayanaKrishna, the king of Dwarka, a central character in the Bhagavata Purana and the Mahabharata and reciter of Bhagavad Gita. However, in the original Dasavatara stotra, Balarama, the elder brother of Krishna, is stated as the eight incarnation, while Krishna (Lord Kesava) is the source of all the incarnation.Gautama BuddhaKalki ("Eternity", or "time", or "The Destroyer of foulness"), who is expected to appear at the end of Kali Yuga. Story can be found in the Kalki Purana.
Note: That last but all three avatars were persons born as kings because creation has proceeded far enough to give birth to enough complex and sophisticated life-forms in Bharatavarsha, that kings are rulers of cities.