I suppose an explanation is in order for the words “Endogenous Retroviruses”: they’re not exactly bandied about in common usage. We’ll start with the second one: Retroviruses. Retrovirus’s? Retrovirii? Freaking plurals how do they work. (Link NSFW: strong language and morons dressed as clowns)
A large number of virus’s reproduce by converting a host cell into a miniture virus factory, to force the host to produce more viruses before it dies. There are several ways of achieving this, but a Retrovirus does it by inserting a section of it’s own DNA into the genetic code of the host cell. The host cell then runs the retrovirus DNA using it’s own molecular machinery, building more viruses and continuing the virus life-cycle.
(Edit: As pointed out by InquisitiveRaven, Retrovirus’s are RNA-based, not DNA based. So in the interests of clarification: the DNA that the virus inserts into the cells genome is not it’s own genome: it’s a copy in DNA format, made with the Reverse Transcriptase enzyme.)
Normally, that segment of virus DNA dies with the cell, which generally doesn’t take very long since a cell is not specifically equipped to manufacture viruses. But sometimes the cell attacked is a reproductive cell, such as a sperm or egg. Now this doesn’t help it at all, unless it goes on to fertilise another reproductive cell and create a creature. That creature will grow up with the viruses DNA, now deactivated, floating around somewhere inside it’s own DNA. This bit of code is an “endogenous retrovirus”, or ERV: virus DNA inside the genetic structure of a non-virus creature.
And if the creature survives to reproduce, and it’s descendants survive to reproduce, eventually that little bit of inactive virus DNA will be found everywhere in the breeding population.
So, keeping in mind that we know what causes ERV’s, we know what they do and how they get put into our DNA, we can compare ERV’s between creatures. If a creature shares an ERV with another creature, than they either share a common ancestor who was “infected” by the ERV, or the exact same type of retrovirus (there are thousands) infected two seperate species in the exact same location in their genetic code.
We share at least eleven ERV’s with both chimps and gorilla’s. If we’re not related to both, then the same type of retrovirus infected all three species in the same location, 11 seperate times.
That’s rather persistant for a co-incidence.
It get’s better. Of those 11, 9 ERV’s are shared with orangutans as well. And 7 are shared with gibbons, 4 with old world monkeys, and 2 with new world monkeys.
(Edit: Aw man, did I screw that graph up? I did. Incorrect graph removed until I can remake it)
This step-wise structure confirms, in spectacular fashion, the tree diagram we’ve already come to expect from other lines of evidence. We’re more closely related to chimps than orangutans, orangutans than monkeys, etc.
I’ve yet to see any anti-evolutionist provide any answer to the mind-boggling number of co-incidences that would be needed to produce this pattern of ERV’s: a quick search of AiG’s website or Creation.com shows the usual response “but they’re not junk! lots of them do something!”. In other words: “Look over there, a distraction!” We don’t care that they do something, we care that we know how they get in and that they confirm the same tree of life we see everywhere in biology. We, and all animals, do not share any ERV’s with more distantly-related creatures that we don’t also share with more closely-related creatures: exactly what the ToE predicts.
We know why and how ERV’s are put into the genetic sequence: we’ve observed it happening. We know what they do, or rather, what they don’t do anymore (regardless of whether or not they’ve been repurposed by the host creature since then). And we know that they form a pattern that confirms and agrees with the nested heirachy that is the Tree of Life. That’s a result that would be spectacularly improbable in a creationist or other anti-evolutionist paradigm that doesn’t require common ancestry.
Of course, if there’s an explanation out there that doesn’t involve evolution, we’re all ears.
I’m in ur genes, endogenizing ur retrovirusez