Recently I've been watching the ABC series Invasion which went off the air in 2006. Impressed with its creativity and its new spin on old ideas. The "Body Snatcher" idea is one of the oldest in sci-fi, and hearkens back to folklore, in tales of doppelgangers and changelings. This particular spin on it is truly interesting, and has provoked my contemplation and brooding long after finishing each episode.
If you aren't familiar with the series, the "aliens" which are never presented as having technology--rather they are biological entities that attack human beings. They look like a cross between giant orange manta rays and trilobytes. They sieze a victim and suck out DNA material. At this point, the creature itself, using the DNA material, metamorphose into replicas of the humans they consumed. In one very well written episode, a botched attack results in a botched replica.
The replicas have memories of their original lives, but they are not human and don't have, apparently, souls. There's something hard, brittle, and coldhearted about them. They don't have consciences. Essentially, the replicas are sociopaths from the get-go.
There is one, however, which has been around quite a while longer than the rest, who was created after a plane crash in the Everglades (the Value Jet crash standing in). He performs a kind of midwife role in the first season. The second season introduces a shadow uber replicant named Zura, who is attempting to achieve a foothold in the American military.
The interesting thing for me, what this show has made me ponder, is the nature of memory. Clearly the replicants have the memories of the human beings they consume/devour/drain/absorb. Memories are nerve impulses stored in our brains. The creatures clearly absorb not only the DNA, but the neural patterns that make up their victim's memories. That's so cool!
This is similar to a discussion of John Carpenter's The Thing, that I was reading the other day. In that discussion, one opinion was that a person infected with the Thing did not necessarily know that they were infected. (Norris). The thing took them over, cell by cell, replicating each cell and neural pathway individually. Not until the underlying Thing consciousness felt threatened, did it reveal itself, rise to the surface, and overwhelm the faux consciousness of the being it had replicated. We see this as Dr. Copper attempts to defibrillate Norris after his heart attack. The Thing considered the electricity an attack, and defended itself. Up until that point, Norris was unaware that he had been transmuted into a Thing, cell by cell.
I wish I could come up with ideas this rich and cool.