The “social chemo-signals,” or vasanas, which are evidence of “the effect of a previous life on one’s current life,” are handed down in the DNA.
We might equate this genetic inheritance with the karma we get from the two people with whom we share our physical substance, our parents.
This prenatal parental karma (an ocean full of the reefs and sharks that Greek tragedy warned us about) is further compounded, especially in early childhood, by our postnatal parental karma (an ocean full of the obsessional reefs and incestuous sharks that Freud warned us about).
We are (as the karma theory demands), more often than not, ignorant of the precise nature
of our parental karma of both types, either because it was made before we were
born or because we have forgotten (or—Freud would say—repressed) it.
There is a long continuum: closest are the things we remember that our parents did for/to us relatively recently, and then the things that they did when we were so little that we
cannot remember them clearly or at all, then the things (like smoking or contracting
AIDS) that our mothers did to us while we were in the womb (here we move back
into prenatal parental karma), then the things that our parents did before we were
conceived, and finally both the genetic stock and the cultural memories transmitted
from earlier generations—the things that happened during the pogroms in Russia,
the traumas suffered during the Great Depression, etc.
Prenatal parental karma gives us our susceptibility to certain diseases and, perhaps, to certain sorts of people; postnatal parental karma, too, may be negative, but it also accounts for the transmission of talents, positive memories such as those stirred by music and art, and irrational love, or the ability (or curse) to fall in love at first sight, generally with a highly inappropriate person.
It is this final piece of the karmic inheritance—irrational love—that is celebrated in the myths (and films) that depict lovers who recognize one another across the barrier of death.
Wendy Doniger, on the Karma of Rebirth