This is a story where, at some time in the nearish future, a group of neuroscientists discover a part of the brain that seems to be critical to conciousness. When this part is destroyed, or removed, the person seems to revert to a more primate form.

This is covered in the news as a breakthrough, that scientists had found the seat of humanity in the brain. Religions immediately declared that organ the vessel for the soul, biologists claim the evolution of this organ was the leap ahead for early man.

At some point in this discussion, though, one group makes the shocking discovery that this organ has vastly different DNA than humans do.

The story progresses for a while trying to keep the media and evangelists and speculators at bay, while trying to sort through this new research area.

In the end, it's discovered that this organ is, in fact, a parasite on the human host. It lives in the human brain, and controls things from there. This, though, is what we are.

We are not the primates, they are our vehicle. We are the parasites driving the primates.

Developmentally, I'd say that there are bits of the human DNA we've injected, such that when the baby is born it is all human, but as the brain "develops", the human body is actually contructing us, the parasite.

Then, somewhere around 2 the parasite hooks in and takes command. It takes a while for it to fully wrap itself around the various systems, which is why we function before a given age, but can't remember anything from the early days.

We weren't actually there yet.

The science in here will get a little dubious, but meh. It's fluffy science fiction, I'm sure it'll be fine...