unred typo said:OK. I’m confused. How exactly did this rare event effect all human and primate DNA? Please explain if the virus event occurred in a single primate and it just happened that all primates living from this time on were descended from this particular primate or did the virus effect all primates living at the time and how did this rare event occur?
Supposing that the same ERV appears in the same place in the genome of all living primates, but in no other animals, we would conclude that the virus infected the sperm or egg of a very early primate, which then went on to form an adult that became the ancestor of all primates living today. This is the only reasonable conclusion. Consider some other possibilities:
1) The ERV was inserted into all living primate species separately by independent viral infections.
Problem: There are about 3 billion base pairs in the human genome, and presumably about that many in the genomes of other primates. If only two separate viral infections were involved, the chances of the ERV getting inserted into the same place each time are about 3 billion to 1. Multiply that by however many other primate species you find the ERV in.
2) The sequence of base pairs that’s being interpreted as an ERV actually came about (either in all the species or in all but one) as a result of random changes to the genome, and not due to viral infection.
Problem: The chances of this are many orders of magnitude lower than for alternative 1 above. ERV sequences are fairly long (several hundred base pairs, I think), and code for recognizable viral proteins (although those codes slowly degrade over time). Such sequences don’t come about randomly, much less in specific places in the genome.
So are there any problems with the accepted interpretation? For instance, is it reasonable to assume that the early primate that originally got infected with the ERV “just happened†to be an ancestor of all living primates. Sure it’s reasonable. No one’s saying that ancestor was the only one in his population to be infected, nor is anyone saying that that ancestor was the only common ancestor of all living primates. Assumedly others that got infected either didn’t have any descendants that made it to the present, or else they did and the ERVs they were infected with are also with us.
The thing about ERVs is that, assuming we understand them correctly, they should show patterns of relatedness. The groups that share an ERV (in a specific place in the genome) should be more closely related to each other than they are to groups that don’t share that ERV. As it happens they do show these patterns (as shown graphically by Quath’s post of July 8), and the patterns of relatedness shown by ERVs are generally consistent with each other and with what we know about relatedness from other sources. For instance, we’ve found several ERVs shared by all primates, and several shared only by Humans and Chimps, but we’ve never found any shared only by (say) Humans and macaques.
So this brings me to another possible alternative explanation:
3) God inserted the ERV into the same place in the genome of the various species being tested.
Problem: OK, but why? Why insert such sequences? They don’t do anything for the organisms in which they’re found. They instead match sequences used by viruses that parasitize those organisms. And why insert such sequences into the same places in the genomes of numerous species? And why do so in a manner to consistently indicate the same pattern of relatedness? Assuming God exists, He must either be deliberately trying to fool us, or else deliberately trying to clue us in. You’ll have to decide for yourself, based on your own interpretation of God’s nature, which you think it is.