What enabled Echo to become a full person?

Question

In Dollhouse, Echo (Eliza Dushku's character) is most notable for how she gradually became a full person. She developed a cohesive identity despite being in doll-state and was able to store the personalities she was imprinted with them in corners of her mind for later access, at times of her choosing. Towards the end of the show, as Boyd's true identity was revealed, he said that Echo was going to be the key to the developing an immunization to being wiped.

But was there ever any valuable information about why Echo? Any moments in the show, even fleeting ones, which offered any insight?

Answer 1

I recall it being stated during the conversation with Boyd that you mention.

Echo/Caroline's spinal fluid was unique due to a specific dormant gene that allowed her resist being reverted to the Tabula Rasa state, and retain imprints. Boyd's plan was to harvest her spinal fluid and use it to create a cure to wiping.

The "full person" she became was, essentially, the Tabula Rasa state learning from the imprints that Echo had received. One very early clue to this was when Echo drew a smiley face on the fogged-up mirror in the Dollhouse's showers, but otherwise appeared to be Tabula Rasa.

Presumably other people also have this dormant gene, but it's a very rare mutation and Echo just happened to be the first doll to ever have it. What happened to Alpha was something else entirely.

Answer 2

The whole gene thing always seemed very unbelievable to me. How did they find out this about her? and was Boyd then waiting for Carolyn or somehow helping Carolyn infiltrate Rossum base so that he could get her to go into the dollhouse program?

It seemed like what also made Caroline special was that she infiltrated Rossum to begin with, so she had an extremely high will to take down something. I always felt it was that will that caused Echo to exist.