You are much more than the sum of your parent’s DNA. Inside your body and brain, a bewildering array of foreign organisms and genetic material has taken up residence alongside what is traditionally known as your “self.” In addition, the complex interactions among all these components could have a profound impact on both your health and behavior.
“Humans are not unitary individuals but superorganisms,” Peter Kramer, a researcher at the University of Padua, told the BBC. “A very large number of different human and non-human individuals are all incessantly struggling inside us for control.”
Kramer, along with Paola Bressan, wrote a paper in July in the journal Perspectives in Psychological Science, calling for psychiatrists and psychologists to take into account the various contributions of these “others” when examining human behavior and mental illness.
Currently, this is a very active area of research, with some solid findings and many ideas that still need to be tested. But it has long been known that what we refer to as our body is actually a complex mixture of genetic material from many sources.
Microbes literally coat our bodies, inside and out. They cover every square inch of our skin and fill our mouths, stomach and intestines. In fact, our gut includes up to 100 trillion microorganisms—ten times the number of cells in the human body. These microbes also contain 100 times more genes than our own.
These bacteria and other organisms, however, are not passive passengers on our bodies. They can communicate with and influence our body, such as shaping what we eat. The exact way in which the microbes communicate with our body is still being explored, but it may involve our nervous, endocrine and immune systems.
Viruses are also known to invade the human body. Often, as is the case with the virus that causes the common cold, a virus comes in, causes trouble and then moves on (as we sneeze on the person sitting next to us on the bus). But in some cases, a virus can stick around for much longer by inserting its genetic material into our own.
If that genetic material happens to end up inside one of our sperm or eggs, then the genes from the virus can be passed onto our offspring. In fact, some of the DNA in our cells that originated from viruses has been around for up to tens of millions of years, long before we had even evolved into modern humans. Kramer estimates that this viral genetic material may make up to eight percent of our DNA.
Some of this foreign DNA from viruses becomes inactive. But certain DNA can remain active—researchers are exploring the link between viral genetic material and mental illnesses such as schizophrenia, and even the development of the placenta in mammals.
It is no surprise that bacteria and viruses eventually end up in our body—we are constantly under attack by microorganisms in our environment. But what may be more shocking is that some of the DNA—or cells—in your body may have come from other people. Which means that you are not the person that you think you are.
One of the most common ways for cells to move from one person to another is during pregnancy, a time in which a fetus actually lives inside the mother. Although the placenta forms a strong barrier between mother and child, many things can pass between the two—including cells. And these can go both ways, from mother to child, or from child to mother.
One recent study found that 63 percent of 59 women tested harbored male DNA in their brains. This maternal-child transfer of genetic material also appeared to occur less frequently in women with Alzheimer’s disease than in women without neurological disease. The exact link between these, though, is not known.
Twins may also transfer genetic material between themselves while them are in the womb. Some research has found that around eight percent of twins actually have two blood groups. It’s possible that this sharing could also involve brain cells. In addition, some people born without a twin may have gained cells from a twin that either never finished developing or merged with the surviving twin early in development.
The overlap between our own “self” and all these other sources of genetic material lines up well with the Buddhist concept of interdependence. There is no clear line that divides “us” from the rest of the world. What is clear, though, is that to understand who we are, we will also need to examine the larger whole that we are part of.
“We cannot understand human behaviour by considering only one or the other individual,” said Kramer. “Ultimately, we must understand them all to understand how ‘we’ behave.”
“We are here to awaken from the illusion of our separateness.” ~ Thich Nhat Hanh