The Ebola virus has captured headlines around the world. One of the big questions that I see being asked frequently is – where did it come from? Does it have a recent origin or has the virus been with us for a long time but simply not recognized? Clearly it didn’t come into existence in 1976 when it was first identified. So how long has it been with us?
The Ebola virus is just one member of a family of viruses that are able to cause hemorrhagic fevers. The other infamous member of this family is the Marburg virus. Both of these viruses exist in the form of several different strains much like there are different versions of the HIV virus that causes AIDS. I refer to them as a virus family because all of these viruses have a similar genomic structure and thus are believed to have a common ancestor. This is to say that at some point in the past there was only a single virus ancestor which mutated to form these two viral “species.”
The question of age then is partly one of how long ago was there a common ancestor of these viruses. An estimate of that time can be derived by looking at how different the genomes are and determining how long that number of errors would have taken to be produced. These estimates vary wildly from 100s of thousands of years to millions of years. Regardless of the age the Ebola virus or something very similar to it has been around for a long time. However it may have only recently appeared in human populations suggesting that humans are not the original host but rather have only lately come to be invaded. Even so, the first incident of human infection was certainly before 1976. In fact, there is some circumstantial evidence that Ebola may have been infecting people in central Africa for hundreds or even thousands of years.
Digging up an Ebola Virus
A few scientists wanted to know, just how old could the Ebola virus be. So they went on a fossil hunt to find an ancient Ebola virus which might help answer that question.
A few months ago I wrote a post entitled: We’re going on a fossil hunt to find a herpes virus. In that post I talked about this type of fossil hunting as a hunt for ancient DNA molecules hiding in genomes of living organisms. I described how this type of fossil hunt is now possible because we have sequenced the entire DNA genomes of so many animals.
How could a herpes or Ebola virus be inside the genome of another animal? Very rarely a virus of this kind when it hijacks a cell to make more viruses it may also invade the genome of the host cell and get integrated into it. If that cell and the host organism survives and that cell is part of a lineage of cells that becomes the next generation of that animal the viral DNA that got inserted into the genome will be passed on to the descendants. Although rare, because these “foreign” pieces of DNA can be copied with the genome to the next generation for thousands and thousands of generations, they can become quite numerous in many animals. For example, it is estimate that 8% of our 3+ billion base pair genome is copies of foreign DNA that were integrated into the genomes of our ancestors and passed down to each of us.
What does this have to do with Ebola? Researchers Taylor and colleagues used the known Ebola virus genome sequences to search for similar sequences in genomes of mammals. What they found was that there were several animal genomes that had copies of some of the genes of Ebola virus integrated into them. One example was especially interesting. They found a portion of the Ebola genome in several species of hamsters and voles. Upon close inspection of exactly were the sequences where in the genomes of these animals they found that an Ebola gene was inserted into the identical location in each of these genomes.
The researchers interpreted this as evidence that Ebola has been around for more than 16 million years!
But how did they come to that conclusion? They reasoned that for hamsters and voles to both have Ebola inserted into their genomes in the exact same location would have required a single insertion event. That original infection, resulting in the integration of the DNA into their genome, must have occurred in the common ancestor of hamsters and voles. That common ancestor is thought to have lived in the Miocene some 16 to 23 million years ago. How that date for the common ancestry is established I don’t want to explore further at this time. The point is that this Ebola virus gene found in these rodents is the “fossilized” remains of a very ancient Ebola infection. An infection that occurred in a population of hamster-like animals that had not yet diverged to become many hamster and vole species.
The same research paper (see below) found that there were several other rodents that have fossil Ebola genes integrated in their genomes but these genes were found in different positions in the rodent genomes. This suggests many separate Ebola infections in their history that resulted in the Ebola virus becoming integrated into their genomes. They also found many bat species also have copies of Ebola genes in their genomes so they too have had a long history with Ebola.
The Ebola virus has apparently been infecting other animals for a very long time. The virus is adapted for living in many animals and other animals are probably adapted to the virus as well. The introduction of Ebola virus into the human population is likely a more recent event. The extreme reaction of our bodies to the virus is evidence itself of its recent ability to invade us. Possibly a mutation in the virus allowed it to invade our bodies much like the HIV virus has also mutated allowing it to infect humans. Since our bodies have not experienced Ebola virus our immune systems are not adapted to dealing quickly enough with the foreign invader and the consequences are devastating. The bats, some of which were also found to have the virus in their genomes, and other mammals that are known to be hosts to the Ebola virus have lived with Ebola for much longer. As a result their immune systems have evolved defenses such that they are not as severely affected. From the perspective of the virus, the ability to live with a host without killing it is to its advantage and is the only reason it has been able to survive for so long. The extreme reaction with human biology would mean that if humans were its only host the virus would have gone extinct long ago or adapted to be more like a flu or cold.
A Creationists Perspective on Ebola?
The very existence of Ebola virus, much less the possible ancient origins of the virus, is a difficult problem for the “very good” creation of the 6-day creation literalists. Answers in Genesis has written on the topic of Ebola several times in the past couple of weeks. One of those articles asked the question: Where did Ebola come from? The author of that article takes notice of the presence of Ebola virus hiding in the genomes of other mammals and responds by saying:
Much to the amazement of many researchers, the whole Ebola genome (DNA) has been found within the genomes of several animals (including guinea pigs, opossums, wallabies, and insect-eating bats). Understanding the origin of this particularly deadly virus helps explain parts of why it is so difficult to treat. If Darwinian evolution were true, then these elements should be considered junk DNA and eliminated from the gene pool by natural selection. However, the presence of these whole genomes in the genomes of other organisms suggests they do something under normal conditions that we have yet to observe.
First of all, it appears the author didn’t read the original research article. It was not the “whole Ebola genome” which was found but rather remnants of some of the genes of the Ebola virus that were found. This renders the authors criticism of “Darwinian” evolution moot since what is found in the genome of hamsters and bats are fragments of Ebola that have undergone rapid mutation because there has been no natural selection to maintain them. The entire Ebola genome was likely once present but most of it has been eliminated from the gene pool over time. So what is observed is exactly what evolutionists would predict to see if the Ebola virus had inserted itself into the host genomes long long ago. The fossils that are left really can be considered “junk” DNA and there is no reason to believe that they are doing something in those genomes that we have yet to observe.
We now have evidence that the Ebola virus has been hanging around prior to the evolution of many species of mammals took place. This doesn’t answer the bigger question – what is the first origin of Ebola virus? Did God create Ebola virus? Was the virus originally a type of living thing that became parasitic and shed its cellular machinery for a life of parasitism? The similarity of many viruses to one another suggests that many viral families have a common ancestor. But do they all have a common ancestor or multiple origins?
Answers in Genesis thinks that viruses were created by God by special creation but were all “good” viruses that only later became corrupted. In other words, they have always been viruses. This raises more questions than it answers. Consider the thousands of viruses that infect animals, if all of today’s species of animals are derived from single pairs of animals on an ark 4500 years ago then those animals would have had to have carried all these viruses in them since each virus must have a host. The ark would have been full of virus-infested animals with most animals harboring multiple viruses at the same time. Consider that there are around 200 known virus species that can attack humans, where were they during the Flood? Most other animals likely have similar numbers of unique viruses.
Secular scientists are divided about the origin of viruses. Some believe viruses are pieces of genomes that have escaped cells and learned a life of parasitism. Others believe they may predate the origin of cells themselves. The many radically different viruses may indicate multiple origins for viruses.
Viruses are the most numerous biological entity on earth and yet we know little about them compared to cell-based living things. The question of viral origins and their original nature is one that is very much an open question and is a subject of much current research.
Brandon Keim, “Genome Surprise: Guinea Pigs Have Ebola!” Wired, July 29, 2010, http://www.wired.com/2010/07/ebola-in-genomes/.
Taylor DJ1, Leach RW, Bruenn J. Filoviruses are ancient and integrated into mammalian genomes. BMC Evol Biol. 2010 Jun 22;10:193. doi: 10.1186/1471-2148-10-193.