The “modern” human is the product of evolution, a natural process that operates on scales ranging from millions, to hundreds-of-thousands, to tens-of-thousands of years. The average individual of today is little changed from the average individual 30,000 years ago. We are literally prehistoric when we are born.
Culture, our ability to pass information, artifacts, and other non-genetic material from one generation to the next, operates on much smaller time scales: millennia, centuries, even decades. The larger cultural landscape consists of religion, language, governments, laws, etc. and many of these change so quickly that they have only been in their present form for hundreds or (in a few cases) thousands of years. It is the blinding speed of culture that has allowed humans to break free of the ecological niche evolution alone would have forced upon them.
One of the subsets of culture is technology, which allows us greater control and understanding of our environment and provides us with new or expanded senses. Technological change occurs on the scale of years to months and is currently outpacing culture at large. The current fad in new technologies is to make these available to a large percentage of the population (literacy, vaccines, video recorders, telephones, etc.) and suddenly many people have the ability to do things for which we have no cultural “rules”.
Sexting is a grand example of the intersection of evolution, culture, and technology. Our prehistoric bodies evolved the desire (possibly need in a normal healthy person) to have sex from puberty on and not just for procreation but for recreation as well  (this is why sex is more fun than, say, wearing matching socks). The American sexual culture , heavily based on Iron Age religions (which tend to demonize sex, especially for women) and the Victorian era “Body Taboo,” has produced a culture that equates nudity with sex (our laws only barely distinguish between the two). The near instantaneous onset of the cell phone camera represents a technology that allows the “biological human” to do something that the “cultural human” abhors. The best examples come from minors sexting semi-nude photos of themselves to friends and later being charged as child pornographers.
This disjunct between rates of evolution, culture, and technology isn’t new. History shows us that our bodies are very bad at evolving to act the way culture tells us; circumcision and homosexuality being grand examples. But the modern drive to make technology available to the masses means that when human desires run counter to cultural rules (“values”, “morals”, laws, etc.) there will be a larger pressure placed on culture to change. Sexting was first reported in the mid 2000s and by 2009 laws were introduced to allow consensual sexting among minors. Presumably faster technological changes will drive faster and faster cultural changes until, someday, some aspects of our culture will be so futuristic they’ll be prehistoric.
1. See Why is Sex Fun? by Jared Diamond and The Naked Ape by Desmond Morris
2. See Sex, Society and History by Vern L. Bullough