Awareness of reincarnation as a potential problem for psychology, biology, and medicine has increased steadily since Ian Stevenson went to India and Sri Lanka (then Ceylon) on his first tour of investigation in 1961. There are now hundreds of reports of children claiming past-life memories published in academic journals and scholarly books11,13,14. As a consequence, some philosophers (e.g.,1,5,10) have begun to consider reincarnation not only as a logical possibility, but as a fact of life.

Critics who dismiss reincarnation case studies as “anecdotal” may not to appreciate the care that has gone into them. Researchers continue to follow the methodology Stevenson pioneered. Along with trained colleagues and assistants native to the countries in which he worked, Stevenson interviewed multiple first-hand witnesses repeatedly over periods of years to check for memory reliability. Whenever possible he consulted police reports, medical records, and other documents to further establish the facts of a case. Stevenson's supporters maintain that his methods rule out social construction along with other potential pitfalls and I will refer to “reincarnation cases” rather than resorting to qualifiers such as “of the reincarnation type.” I believe the data are now robust enough to take the possibility of reincarnation seriously, despite the challenge to physicalist assumptions this entails. However, I do not mean by my terminology to forejudge the evidence in any particular case or to insist that reincarnation is the only conceivable interpretation of the case data as a whole.

In many reincarnation cases, children's memories are detailed enough to pinpoint the deceased person with whom they identify (the “previous person”). When identifications are made, it becomes evident that not only are the claimed memories accurate by and large, there are similarities of personality and behavior between the case subject and previous person. In addition, case subjects may have physical traits corresponding to physical traits of the previous person. Congenital physical abnormalities (CPAs) such as birthmarks and birth defects appeared in roughly 35% of the cases in Stevenson's collection (21, p. 404). Although they were most often associated with mortal wounds, birthmarks and birth defects did not invariably present when one might expect them to and appeared in relation to a variety of other traits as well (e.g., healed surgical scars, earring holes, tattoos, and so forth:22).

Another finding from this research is the great variability in the length of the interval between lives (the “intermission”). In verified or “solved” cases, the interval has been found to be as long as several decades or as short as a few hours. In principle, the intermission might have no appreciable duration, that is, the previous person's death may coincide with the subject's birth. Cases with intermissions of less than 9 months—a shorthand reference to the gestation period, regardless of actual length—are of particular interest philosophically and theoretically because they raise the question of when a reincarnating essence joins its new body.

Importantly, Stevenson discovered that CPAs may appear in cases with intermissions of under 9 months, some no longer than a few days (1997a, p. 1095). He did little to address the theoretical implications of this finding, however. In this paper, I probe the effect more deeply. I consider explanatory models alternative to reincarnation, such as maternal impression or psychic actions by living persons, that could account for reincarnation cases in general and explore the implications for biology and medicine of CPAs in cases with intermissions under 9 months in length.