Naturally occurring, physiologically normal, primate chimeras.

Callitrichids, South American primates including marmosets and tamarins, have evolved a unique physiology. Twins share a placenta during gestation and exchange stem cells, resulting in naturally occurring chimeric adults. Our study used a quantitative PCR-based assay to address whether this chimerism was restricted to blood and other cells of the hematopoietic lineage or whether it extended to other somatic tissues. These studies help to characterize species that have adapted evolutionarily to pervasive chimerism, with every individual healthy and unperturbed. This experiment of evolution offers insight into transplantation and histocompatibility, reproductive biology and behavior, and innate and adaptive immunity.