“Nature is only another chimera.”
Chimerism and the Cells of Mother and Child
Genetic chimerism is a phenomenon that illustrates the extent to which we are all interconnected, and even, biologically, a part of one another. In the past, it was common for societies to mythologize natural phenomenon of which they had little scientific understanding. The Greek myth surrounding chimerism depicted Echinda, half snake and half nymph, who was mother to the Gorgon, the Hydra, and the Chimera. The chimera has been described differently by different cultures. In the “Illiad”, Homer describes it as a combination of a goat, a lion and a snake.
The myth illustrated the terror associated with the prospect of mothers not having control over which parts of themselves their children will inherit. Today, there is a scientific explanation for chimerism, or one individual organism carrying the cells of another separate organism within it. The cells of mother and child may be shared to a greater extent than previously realized. According to one article, one example of this is the placenta, which is an organ built from the cells of mother and child, through which the child receives nourishment throughout the process of gestation. Cells from the placenta can migrate to almost any other organ in the body, including the heart, kidneys, and even the skin. These cells can serve positive purposes, like tissue repair or preventing cancer.
Some evidence suggests that cells can also be transferred from mother to child through nursing. These cells, like stem cells, can become many types of tissue and serve to assist in tissue repair of damaged organs. An experiment with a mother rat with an injured heart showed that the fetal cells migrated to the heart, where they became heart cells that helped repair the damage. In other animal studies, microchimeric cells were found to have become nerve cells in maternal brains, leading researchers to believe that they may serve a similar purpose in humans.
The Cells of Mother and Child in the Brain
The modern concept of individuality is somewhat challenged by the fact that most people carry remnants of other individuals within their bodies. A new study shows that these remnants, or cells, are also found in the brain. In the study, living male cells, some of which had survived for several decades, were found in the brains of women. It was also found that these cells were less common in women suffering from Alzheimer’s disease. Further research may one day reveal exactly what impact the cells of mother and child have on brain health.
Another study examined the brains of deceased women. They found the presence of cells containing the male chromosome in more than 60 percent of the brains. Further, they were found in multiple regions of the brain. This study disproved the theory that Alzheimers may be caused by the presence of these cells. Rather than being more common in women who’d had multiple pregnancies, it was more common in women with fewer shared cells.
The Role of Cells of Mother and Child in Continuity
In the first reported case of chimerism, that of Mrs. McK, it was found that a twin had been absorbed in utero, which resulted in her having two distinctly different blood types. The majority of chimeras are, or were at one time, twins who exchanged blood in utero. In rare cases, the DNA of a child lost in utero has been absorbed by the mother’s body, transforming her into a chimera born of grief and the desire for her child to experience life.
In the case of Lydia Fairchild, DNA tests ordered by the state to prove the paternity of her two children confirmed that she was not their genetic mother, despite having given birth to them. Accused of welfare fraud and threatened with the removal of her children by the state, her lawyer demanded further testing and it was revealed that she carried two distinct strands of DNA. This results when two sperm implant two eggs and is called tetragametic chimerism. Her case illustrated that DNA may not offer the 100% positive proof of individual identity that we believe it does. It also suggested that we may not always pass as much of ourselves to our children through our own DNA as we believe we do.
Scientific Experimentation with Chimerism
A “geep” was created in 1984 by British geneticists who combined the embryos of a sheep and a goat. The resulting chimera was sterile, but lived to adulthood. Other scientists have experimented with rabbits with blood containing human cells. These experiments are distinctly different from the naturally occurring phenomenon of the combining of the cells of mother and child and some ethical considerations have been raised surrounding them. While such experimentation may one day increase our understanding of our own humanity, there is no substitute for the genius of mother nature.