Parents go to great lengths to ensure the health and well-being of their developing offspring. The favor, however, may not always be returned.

Dramatic research has shown that during pregnancy, cells of the fetus often migrate through the placenta, taking up residence in many areas of the mother's body, where their influence may benefit or undermine maternal health.

The presence of fetal cells in maternal tissue is known as fetal microchimerism. The term alludes to the chimeras of ancient Greek myth--composite creatures built from different animal parts, like the goat-lion-serpent depicted in an Etruscan bronze sculpture.

According to Amy Boddy, a researcher at Arizona State University's Department of Psychology and lead author of a new study, chimeras exist. Indeed, many humans bear chimerical traits in the form of foreign cells from parents, siblings or offspring, acquired during pregnancy.

"Fetal cells can act as stem cells and develop into epithelial cells, specialized heart cells, liver cells and so forth. This shows that they are very dynamic and play a huge role in the maternal body. They can even migrate to the brain and differentiate into neurons," Boddy says "We are all chimeras."