These three videos explain this extremely powerful evidence for the evolutionary relationship between modern human apes and the other modern ape species. Scientific evidence can't be any stronger than what molecular biologists have discovered about ERVs. There are countless smoking guns that make evolution an established truth. This is one of them.
If you run the numbers with the assumption that ERVs can only insert in 1% of the genome, i.e. highly nonrandom, you still get enormously low probabilities with only 16 ERVs. So even if insertion is highly nonrandom, getting the thousands of matched ERVs between all primates is unbelievably unlikely just like I show in the video (don't believe me, do the math). Endogenous Retroviruses (ERVs) are the relics of ancient viral infections preserved in our DNA. The odd thing is many ERVs are located in exactly the same position on our genome and the chimpanzee genome. There are two explanations for the perfectly matched ERV locations. Either it is an unbelievable coincidence that viruses just by chance inserted in exactly the same location in our genomes, or humans and chimps share a common ancestor. It was our common ancestor that was infected, and we both inherited the ERVs. ERVs provide the closest thing to a mathematical proof for evolution. And remember, ERVs are just one of the millions of FACTS that support the theory of evolution. Think about it.
The owner of http://scienceblogs.com/erv/, Abbie Smith, answers the question "Does Molecular Genetics Support Human Evolution?" at this video: Abbie Smith: Does Molecular Genetics Support Human Evolution? She also explains the many different ways creationists lie about this evidence, and why they are wrong.
Another excellent video about ERVs: Evidence of Common Ancestry: ERVs
We also harbor dead genes that came from other species, namely viruses. Some, called 'endogenous retroviruses' (ERVs), can make copies of their genome and insert them into the DNA of species they infect. (HIV is a retrovirus.) If the viruses infect the cells that make sperm and eggs, they can be passed on to future generations. The human genome contains thousands of such viruses, nearly all of them rendered harmless by mutations. They are the remnants of ancient infections. But some of these remnants sit in exactly the same location on the chromosomes of humans and chimpanzees. These were surely viruses that infected our common ancestor and were passed on to both descendants. Since there is almost no chance of viruses inserting themselves independently at exactly the same spot in two species, this points strongly to common ancestry. -- Jerry Coyne