When do we cross the line from 'animal' to 'person?'

[Little Rik]

So........who give the animals the instinct?
Santa?

Instinct, like all evolved traits, is a result of natural selection. Individuals displaying a new useful trait in the phenotype are more likely to reproduce. Such alterations occur because the replication process is sensitive to environmental variation. Of course almost all replication errors, (mutations), don't result in useful change.

I tried to go well behind this physical reality.
It is true that creature have to adapt to the particular reality in which they are living but i am not talking about this.
I am rather talking about how a particular creature get in a particular body.
When a kidney need to be transplanted into a different body first of all the doctors will have to find out if the recipient will be ok with that organ or it will reject it so they will have to do some research and only then proceed with the transplant.
In the same way when a creature (soul or spirit) will have to be reborn will have to be reborn in a particular body which will be in tune with their spirit.
In other words it is not a body that will be determinant in shaping a new creature similar to herself but is God that decide the best medium in which to put a particular soul with a particular body.
If the mind is not developed enough then it will be driven by instinct and therefore will end up in an animal body, if on the other hand it will be developed enough will end up into a human being body so according to me your analysis only deal with the physicality which in no way can answer where the mind or instinct come from.