That's 3 in 4 adults have either type!
1 in 4 adults have either type of herpes or both types, about 75% of the population does not know they have herpes because the symptoms are so mild and go unnoticed
They are viruses that are specialized in infecting human cells, such as nerve cells. The HSV1 and HSV2 viruses are harmless most of the time and spread when enough of the virus is rubbed into the skin of another person and takes hold in their nerves.
Why is it so prevalent amongst humans? Is it basically a virus that's harmless most of the time and spread through almost any means?
Depends on what you mean by herpes. There is a collection of viruses termed herpes. They are all distinct viruses although some are somewhat similar in their DNA.
Some of the individual viruses are found in over 90% of the population. The worldwide incidence of HSV1 for example is probably over 65%.