Many of these DNA sequences don’t seem to do anything in the human body, but retrovirus infections allowed our distant ancestors to acquire the capacity to perform functions that are fundamental to human existence. One remarkable example is a gene inherited from a retrovirus infection about 400 million years ago that plays a crucial role in memory formation. The gene does this by coding for tiny protein bubbles that help to move information between neurons, in a manner similar to the way that viruses spread their genetic information from one cell to another.
