"The Padma Purana says that there are 8,400,000 species of life, and the soul evolves through them. This evolutionary process we accept: the soul evolves from aquatics to plants,
to insects, to birds, to animals, and then to the human forms. But all these forms are already there. They do not change. One does not become extinct and another survive.
All of them are existing simultaneously."
http://www.angelfire.com/ego2/prabhupada/evolution.htm