Tuesday, October 22, 2013

Virus out of Africa

Map of geographic spread of HSV1
Figure 4 from the article, showing proposed dispersion patterns of HSV-1.
Although Mesopotamia, the area around the Tigris and Euphrates Rivers in what is now Iraq, was long considered to be the cradle of human civilization, the general scientific community places the origins of humans in Africa.  The "out-of-Africa" theory claims that humans initially evolved in Africa, spread northward into the Middle East, then eastward and westward to Asia and Europe.  The book of Genesis, on the other hand, records post-Flood civilization as beginning somewhere around Turkey, where Noah's Ark landed, migrating to Mesopotamia (Babel), then dispersing from there to Africa, Europe, and eastern Asia, and eventually the rest of the world.

Now, a study from the University of Wisconsin-Madison  claims to have found support of the "out-of-Africa" theory.  This study analyzed the genomes of numerous samples of the herpes simplex virus 1 (HSV-1) from around the world, namely from the UK, USA, China, Kenya, South Korea, and Japan.  Using cladistic analysis, a quantitative technique for determining evolutionary relationships using similar features, a sort of family tree (cladogram) was developed that chronicles the history of mutations in the viral genome.  According to the cladogram, it appears that the virus started in Africa, then spread to Asia and Europe, and ended up in North America via both European and Asian migrations.  Because the virus infects and is spread by humans, it is assumed that the migration of the virus would closely follow human migration patterns.  Therefore, the authors conclude that the study presents strong evidence for the "out-of-Africa" model.

Admittedly, I am no expert on viral genetics, and this study did give me pause at first.  Eventually, however, I decided that it does not necessarily support the evolutionary model over the biblical model, as I have two issues with the study.

First, there is no data from the Middle East included in the study.  In fact, a majority of the samples seem to be from Kenya (15 samples) and the US (10 samples), plus two samples each from Japan, South Korea, and the UK, and one from China.  It should come as no surprise, then, that four different clades (groups) were found in the African samples, one in the Asian samples, and one in the European/North American samples (as a further note, one of the North American samples actually matched the Asian ones, and was attributed to the Bering Strait migration).  The number of African clades is used in part to justify the African origin, but the high proportion of African samples in the total study sample may bias this.  I would be interested to see what impact a set of viruses from the Middle East has on the analysis, because the cladogram does not appear to rule out a Middle Eastern origin.

Second, there is the assumption that the virus co-evolved with humans.  I think it is reasonable that the virus itself could have originated in Africa, with humans originating elsewhere, and still have produced this genetic pattern.  Even if we grant that the number of African clades supports an African origin, it is only an origin of the virus, not of the people it was infecting.  I can imagine that this assumption was made due to a view that the virus must have evolved along with humans and other mammals in order to be specific to their hosts.  Given this belief, I can understand how the study can be seen as supporting the idea that humans evolved out of Africa, but I cannot honestly say it actually provides sturdy evidence for it.

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