As most of you might know that in Hinduism, it is believed that you and every other living thing consist of two things one is "a soul" which is indestructible, true and reality. No harm can be done to the soul. The other is your "body" which is illusion. It is destroyed after you die. Your soul then gets free from your body when your body dies and goes to another body it calls rebirth.
Every soul has to pass through several species as per evolutionary process. According to Padma Purana, the different types of life-forms in the universe are 8,400,000:
900,000 of which are aquatic ones; 2,000,000 are trees and plants; 1,100,000 are small living species (like- insects and reptiles); 1,000,000 are birds; 3,000,000 are beasts and 400,000 are human species.
Only after passing through all of the above forms will a soul get its human form. As we can say the soul inside of a human is the same as that of a soul inside of an ant or an elephant.
The cycle of birth and death continues on until it is merged with the Supreme One called "Paramatma" (or a soul gets free from the cycle of rebirth). This is called "Moksha". The time taken for the Moksha will depend upon one's "Karma" and "Dharma".
For example, as we know for the sake of food, a Tiger kills a Deer, Plants are killed by Elephants, a Snake kills a Rat, and we, humans, also kill many things like plants and animals for food (or for habitat) and so on. As per my knowledge the above all have done the same karma or sin. But as we know if human's karmic account is not clean, he will only be wandering in different planes of existence in different kinds of bodies suffering or enjoying different kinds of pain and pleasure depending upon his actions (karma) respectively.
My questions are:
Does it mean the 8,400,000 forms are created simultaneously at one time?
If yes, then, does it mean some souls are coming directly to human-form?
If not, then, why is a specific number of life-forms given in Padma Purana?
Does Karma apply to all life-forms?
E.g., can the soul of a tiger take birth as tiger only or can it go to a lower life-form according to its karma (by killing a animal for the sake of food)? Or will it always gain a higher life-form of the evolutionary process?
How to know that it's their result of karma or it's their own way of life (it means no prarabdha karma generated and they will go direct to higher life-form)?
Is there any possibility of skipping one life-form of evolutionary process and go upward or downward? Specially, does this happen in humans i.e., going to a lower life-form? (Higher simply means attaining moksha, as per my knowledge)
Does this karma only apply to humans?
Are there any scriptural references for any of this?
UPDATE: Added one more question related to this topic.