I've been reading "When the Impossible Happens" by Dr. Stanislav Grof. He's famous for his research into the psychotherapeutic use of LSD and the invention of holotropic breathwork (HB), which recreates to some degree the effect of psychedelic drugs.
Grof describes people under the influence of LSD or HB who relive being children undergoing trauma. The interesting aspect is, the lives they're reliving aren't their own. There's no history of the event in their autobiography. Puzzled, they then mention what they experienced to a parent or grandparent only to find out that the experience belonged to that parent or grandparent without the experiencer having heard about it before. This raises the question of whether there is cellular memory that is passed on through the genes.
But we know from hypnosis regressions that people can also very vividly experience lives from times past for which there can be no genetic connection. And they can exhibit marks on their body that correspond to traumas experienced by the person whose life they [allegedly] relived from some distant, far away place. So I don't think cellular memory explains it.
Under hypnosis, or even when I'm in the hypnogogic state before falling asleep, I get fleeting images of people and places that are quite vivid. Many are clearly from long ago in history. Yet, I have no sense of identification with any of them. The images don't seem to correspond to what could be termed a memory. So where do they come from?
If you think of the universe as having a universal consciousness, or as the trancendentalists called it, an oversoul, then the individuated soul or consciousness is, as has been postulated, much like a bay in an ocean. That sea of consciousness contains all of our experiences, past, present and future. Some call it the akashic record, and liken it to a book. So perhaps what I experience with my fleeting images corresponds to randomly opening that book and seeing an excerpt from someone's life.
So how do we identify that which is ours versus that which resides in someone else's [memory]? Under hypnosis, people can relive past-life traumas and have reactions that, cathartic in nature, relieve some emotional or even physical malady in this life. I think it's safe to say that if you start in this life by focusing on a malady or issue, it can lead back to the underlying trauma that belongs squarely in the person's own past-life bay. There's an emotional connection that links the past and present. If you regress a person to a past-life without an objective in mind, you come up with far less vivid and meaningful past-life experiences that in many cases, seem either confabulated or irrelevant to the present life.
I can't tell you how many people go back to see themselves, for example, as a Roman centurion. Nobody ever says I was a quaestor or a tribune or any of the other obscure Roman ranks. They always say centurion. My hypothesis is that if there's no emotional connection, the mind uses what it knows consciously to either confabulate or go to some page in the akashic record that seems familiar. So, while most people are aware of Rome and centurions, thanks to Hollywood, not many know the other Roman legionary ranks or for that matter, anything about other empires or cultures existing in the past. Nobody says I was a Scythian archer, for example.
The people who experienced the childhood of their parent or grandparent have an emotional link with that parent or grandparent, which may serve as a pathway to a given [pool] of consciousness. The emotional baggage that the parent or grandparent carries apparently serves as a beacon and as I've said before, the more emotional energy is carried by a person, the more the soul will be drawn to it.
Perhaps the person who thinks he or she was a certain famous person in history is, like the person claiming to be a Roman centurion, using conscious knowledge as a path to the [memory pool], so to speak, of that famous person. And if there are similarities between the present-life person and the past-life person, it may be that there are emotional similarities as well. And that could draw the soul into the famous person's [memory], mistakingly believing it to be their own.
In that case, the matter of physical characteristics becomes more acute. If someone has the mark of physical trauma that corresponds to a previous life experience, then it likely is the person's past-life. But what of similarities in appearance? I don't think that can be a reliable guide to identifying a past-life without there being some kind of emotional connection. Similarities in appearance, interests, and personality with a past-life person can lead the mind to [pools] of consciousness that the present-life person identifies with and thinks might be a memory. I suspect a more reliable guide would be the present-life person's emotional reaction to a past-life episode and more importantly, the effect that reaction has on the present-life person's issues. Remembering you're [someone like] Thomas Jefferson may result from identifying with his life. But unless there's an [actual] emotional connection between you and Jefferson, it's less certain that you didn't just go to the wrong [pool] of consciousness.