Problem:

I was just reading Evolution of lactose tolerance, and in it one line says "But there was a time in human history when our diet and environment conspired to create conditions that mimicked those of a disease epidemic".

Something I've always wondered is rather than natural selection occurring and survival of the fittest and so on, is that a viral epidemic caused a mutation in the survivors, i.e. DNA was inserted from the virus that modified the survivors genome. There is some evidence that a significant percentage of the human genome comes from viruses. Probably a naive question - so is there any evidence that this has occurred? From my lay perspective this is what attempts at genetic engineering use, so it's possible nature already did this?

It's always seemed to me that natural selection and point mutations, and the chance meeting of two people with the same mutation would be too slow and viruses would be a more efficient method to evolve a large population at the same time. Things like punctuated evolution might support this? not really sure.

Please suggest your ideas.