I will begin this essay by quoting the intelligent design blog Uncommon Descent:
"Endogenous retroviruses are molecular remnants of a past parasitic viral infection. Occasionally, copies of a retrovirus genome are found in its host’s genome, and these retroviral gene copies are called endogenous retroviral sequences. Retroviruses (like the AIDS virus or HTLV1, which causes a form of leukemia) make a DNA copy of their own viral genome and insert it into their host’s genome. If this happens to a germ
line cell (i.e. the sperm or egg cells) the retroviral DNA will be inherited by descendants of the host. Again, this process is rare and fairly random, so
finding retrogenes in identical chromosomal positions of two different species indicates common ancestry."
So let's review: On a rare occasion a virus will insert itself into it's host's genome at random, and the host's descendants will inherit this and have the virus in their genome. Our genome is 3 billion base pairs, so it is extremely unlikely that any creature would share the exact same virus in the exact same place in the genome. But yet humans and primates do have the same viruses in the same places in their genome. This is because they were inherited from a common ancestor.
The above article was written by Douglas Theobald, the assistant professor of biochemistry at Brandis University.
In order to prove this truly is evidence of evolution, let me consider the following questions:
1. Is the viral insertion really random?
Yes. Here are two papers creationists use in support
of the nonrandom viral insertion hypothesis:
http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020234&ct=1
http://www.genetics.org/cgi/content/full/158/2/769
The first paper simply states that some retroviruses like to insert in genes, some like to insert near promoters of genes, and some like to insert in the middle of no where. The specific insertion sites, what base pairs on on the left, which ones are on the right, is random. Thats exactly what they looked for in that papers methods.
In the second paper the researchers found two independent Viral insertions in deer mice. They could tell the insertions apart because the virus had infected two different places, because this event happened twice.
So Retroviral insertion is indeed random.
2. Do the Viruses serve any good purpose?
No. When ERV's do become functional, they cause
disease:
http://www.arthritis.arizona.edu/HERV.htm
http://www.mylonglife.com/articles/Retroviruses_Aids_Cancer_And_Autoimmune_Diseases.htm
In closing, you can google "endogenous retrovirus" and pull up plenty of medical, scientific, and educational websites. If you email the website, they will tell you
the exact same thing I am. You could also visit a university and contact a geneticist who will provide you with the same information.
Some of this material was referred by Abbie Smith in her series "Common Creationist Claims About ERV's"
If you are still having trouble understanding, try watching this video:
