What behaviors are ethically off-limits for most people in the United States? Perhaps unsurprisingly to those who have read The Scarlet Letter, the greatest taboo is adultery. The overwhelming majority of Americans see married men and women having an affair as the most morally repugnant of all 19 behaviors surveyed. In fact, just eight percent say extramarital affairs are acceptable, a new Gallup poll finds, which is a one percent uptick from 14 years ago.

Interestingly, the age group that finds extramarital affairs least palatable are not seniors, as might be expected, but 30- to 49-year-olds — presumably, many in this age range have children at home.

Gallup reports the biggest gains in ethical tolerability for two extremely different issues: the cloning of humans and polygamy. Today, three in every 20 Americans find cloning humans morally permissible, more than double the number from 14 years ago. Notably, a full third of those surveyed remain unbothered by the cloning of animals; this represents a slight uptick in the numbers when compared to 2001.

The acceptability of polygamy, which is illegal in all 50 states, has also doubled: from seven percent in 2001 to 16 percent of Americans finding marriage to more than one person acceptable today. In 2006, Gallup recorded the lowest number of people backing this particular behavior: only five percent of those surveyed found this behavior morally tasteful. Interestingly, Big Love, a critically acclaimed TV show about a man married to three wives, began in 2006 and ran for five years.

What’s on the list?

It must be noted that many behaviors and issues that some might expect to find on the list of 19 moral behaviors are absent. People’s attitudes about gambling were surveyed, for instance, while their feelings about illicit drug use, say, or promiscuity were not. Results for this Gallup poll are based on telephone interviews of a random sample of 1,024 adults throughout the nation; the margin of sampling error is plus or minus four percentage points.

Pornography is considered “not a moral issue” by one percent of Americans, while 62 percent find it “wrong,” a decrease of four percentage points over the past 14 years. However, senior citizens find pornography more contemptible than other age groups, with only 18 percent supporting its use.

Finally, the acceptability of having a baby outside of marriage rose by a decent percentage: 61 percent of Americans find this behavior morally palatable today compared to 45 percent in 2001, a full 16 points higher.