Where exactly is sex desire located: in the body or the soul?

From: Rupak

Can you please explain in detail about origin, manifestation, transformation of sex desire. Let me put the question as below. Where is actually the sex desire. We understand from scriptures that the desire to enjoy separate from Krishna ( kama ) is the root of material existence and a sure characteristic of a conditioned soul.  Then it manifests as gross attraction for the body of opposite sex.

The confusion as below.

1. one species is attracted only to one’s own species of opposite gender.  so when does the soul identifies with a particular species. for example we had one article about ghosts. they dont have a gross body. still they think they are male/female humans and may try to fulfil their sex desire. But actually he does not have a gross body now. So if that soul is going to get a body of dog next time then when will he start having the desires’ of a dog.

2. there are some class of people called asexuals. I dont know if they really exist but dictionary definition is these are people who dont have any sexual attraction to both males and females. So I am not able to understand if this desire is a manifestation of the root desire to enjoy separate from Krishna which is a must characteritstic of a conditioned soul how can they be free from it without doing any spiritual practice.

So it looks like this desire has origin in the body/body type and not in the soul. Please explain how to understand the shastric statements that this is a disease of any conditioned soul.