About a month or two ago, I was given a small box emblazoned with the iconic, yellow, rectangular logo of “National Geographic.”  Across the box was a graphic of the silhouette of a lone man walking across a patch of land.  The box was a kit as part of “The Genographic Project,” and the lone man in the graphic represented “Adam,” the ancestor all living humans descended from.  Inside the kit, one finds many colorful brochures detailing what exactly the Genographic Project is, in addition to a pair of test tubes and cotton swabs.  The directions instruct one to swab the inside of his cheek for DNA, place the swab in the test tube, and mail the package back to National Geographic to be processed.

As described on the website, “the Genographic Project is a five-year research partnership led by National Geographic Explorer-in-Residence Dr. Spencer Wells. Dr. Wells and a team of renowned international scientists and IBM researchers, are using cutting-edge genetic and computational technologies to analyze historical patterns in DNA from participants around the world to better understand our human genetic roots.”  More information can be found here: https://genographic.nationalgeographic.com/genographic/lan/en/index.html

I swabbed my cheeks, mailed in my kit, and began the waiting game some weeks ago.  Every few days, I would check the website to see if my DNA samples had been processed yet.  Finally, today, my results had arrived.  The scientists tracked my Y-chromosome, which follows the migration of one’s paternal ancestors.  Based on my results, my ancestors left Africa some 60,000 years ago, went to the Middle East, and finally arrived in Europe between 8,000 to 20,000 years ago.

As I read about my prehistoric ancestry, I was intrigued by the idea of the existence of an actual “Adam,” so I looked into the matter further.  According to National Geographic, “new DNA studies suggest that all humans descended from a single African ancestor who lived some 60,000 years ago” (http://news.nationalgeographic.com/news/2005/06/0624_050624_spencerwells.html).  While this man is referred to as “Adam,” he was not the only man alive in his era.  Rather, he is special because the DNA of everyone living can be traced back to him.

That last fact made me think about what we have been learning recently in class about epidemics and social contagions.  We are all truly the result of a social contagion, of which Adam is at the head of our genealogical tree.  One caveat exists between social/biological contagions and this example.  Adam can only spread his offspring to the next wave of people through successful reproduction.  Consider the first wave of the branching process to include all of the sexual partners Adam had.  The second wave is then the offspring of the first wave (Adam’s children).  The third wave is then Adam’s grandchildren.  Each node on this tree that successfully reproduces transmits Adam’s DNA to the next wave.

Simultaneous to the transmission of Adam’s DNA, thousands of other branches were spreading from other individuals, as well.  The remarkable thing to consider is that of all the branches occurring, only one has survived to the present day.  Adam’s branches can be said to have high contagion probability, as they successfully passed on to the next generation.  The many other branches that died out can be considered to have low contagion probability, or at least lower than Adam’s.  The transmission of Adam’s DNA, then, has a probability of R0 > 1, because his genetics persist by continuing on to at least one person in each wave.  The DNA of the many branches that have died out has probability of R0 < 1, because each of these sets of genes died out after a finite number of waves.

In addition to the epidemic nature of the spread of genes, there is obviously a great deal of biological and evolutionary actions occurring.  It would be very interesting to explore these fields in greater depth.