In a landmark 1936 paper, Turing laid out a set of simple mechanical operations that was sufficient to compute any mathematical or logical formula that was computable at all. These operations could easily be implemented in a machine -- a digital computer -- and a decade later Turing designed a practicable version that served as a prototype for the computers we use today. In the interim, he worked for the British decryption unit during World War II and helped to crack the cipher used by the Nazis to communicate with their U-boats, which was instrumental in defeating the German naval blockade and turning around the war. When the war was over, Turing wrote a paper (still widely read today) that equated thinking with computation, thereby offering an explanation of how intelligence could be carried out by a physical system. For good measure, he then tackled one of the hardest problems in science -- how the structure of an organism could emerge from a pool of chemicals during embryonic development -- and proposed an ingenious solution.

It would be an exaggeration to say that the British mathematician Alan Turing explained the nature of logical and mathematical reasoning, invented the digital computer, solved the mind-body problem, and saved Western civilization. But it would not be much of an exaggeration.

At least since Leviticus 20:13 prescribed the death penalty for a man lying with mankind as he lieth with a woman, many governments have used their monopoly on violence to imprison, torture, mutilate, and kill homosexuals. A gay person who escaped government violence in the form of laws against indecency, sodomy, buggery, unnatural acts, or crimes against nature was vulnerable to violence from his fellow citizens in the form of gay-bashing, homophobic violence, and antigay hate crimes. Homophobic violence, whether state-sponsored or grassroots, is a mysterious entry in the catalog of human violence, because there is nothing in it for the aggressor. No contested resource is at stake, and since homosexuality is a victimless crime, no peace is gained by deterring it. If anything, one might expect straight men to react to their gay fellows by thinking: "Great! More women for me!" By the same logic, lesbianism should be the most heinous crime imaginable, because it takes women out of the mating pool two at a time.

What did Turing do to earn this stunning display of ingratitude? He had sex with a man. Homosexual acts were illegal in Britain at the time, and he was charged with gross indecency, under the same statute that in the preceding century had broken another genius, Oscar Wilde. Turing's persecution was motivated by a fear that homosexuals were vulnerable to being entrapped by Soviet agents. The fear became risible eight years later when the British war secretary John Profumo was forced to resign because he had had an affair with the mistress of a Soviet spy.

How did Western civilization thank one of the greatest geniuses it ever produced? In 1952 the British government arrested him, withdrew his security clearance, threatened him with prison, and chemically castrated him, driving him to suicide at the age of forty-two.

Homophobia is an evolutionary puzzle, as is homosexuality itself. It's not that there's anything mysterious about homosexual behavior. Humans are a polymorphously perverse species, and now and again seek sexual gratification from all manner of living and nonliving things that don't contribute to their reproductive output. Men in all-male settings such as ships, prisons, and boarding schools often make do with the available object that resembles a female body more closely than anything else in the vicinity. Pederasty, which offers a softer, smoother, and more docile object, has been institutionalized in a number of societies, including, famously, the elite of ancient Greece. When homosexual behavior is institutionalized, not surprisingly, there is little homophobia as we know it. Women, for their part, are less ardent but more flexible in their sexuality, and many go through phases in life when they are happily celibate, promiscuous, monogamous, or homosexual; hence the phenomenon in American women's colleges of the LUG (lesbian until graduation).

But homophobia has been more prominent in history than lesbophobia. While many legal systems single out male homosexuality for criminalization, no legal system singles out lesbianism, and hate crimes against gay men outnumber hate crimes against gay women by a ratio of almost five to one.

The evolutionary mystery is how any genetic tendency to avoid heterosexual sex can remain in a population for long, since it would have consigned the person to few or no offspring. Perhaps "gay genes" have a compensating advantage, like enhancing fertility when they are carried by women, particularly if they are on the X chromosome, which women have in two copies -- the advantage to women would need to be only a bit more than half the disadvantage to men for the gene to spread. Perhaps the putative gay genes lead to homosexuality only in certain environments, which didn't exist while our genes were selected. One ethnographic survey found that in almost 60 percent of preliterate societies, homosexuality was unknown or extremely rare. Or perhaps the genes work indirectly, by making a fetus susceptible to fluctuations in hormones or antibodies which affect its developing brain.

The real puzzle is homosexual orientation -- why there should be men and women who consistently prefer homosexual mating opportunities to heterosexual ones, or who avoid mating with the opposite sex altogether. At least in men, homosexual orientation appears to be inborn. Gay men generally report that their homosexual attractions began as soon as they felt sexual stirrings shortly before adolescence. And homosexuality is more concordant in identical than in fraternal twins, suggesting that their shared genes play a role. Homosexuality, by the way, is one of the few examples of a nature-nurture debate in which the politically correct position is "nature." If homosexuality is innate, according to the common understanding, then people don't choose to be gay and hence can't be criticized for their lifestyle; nor could they convert the children in their classrooms or Boy Scout troops if they wanted to.

Whatever the explanation, people with a homosexual orientation who grow up in a society that does not cultivate homosexual behavior may find themselves the target of a society-wide hostility. Among traditional societies that take note of homosexuality in their midst, more than twice as many disapprove of it as tolerate it. And in traditional and modern societies alike, the intolerance can erupt in violence. Bullies and toughs may see an easy mark on whom they can prove their machismo to an audience or to one another. And lawmakers may have moralistic convictions about homosexuality that they translate into commandments and statutes. These beliefs may be products of the cross-wiring between disgust and morality that leads people to confuse visceral revulsion with objective sinfulness. That short circuit may convert an impulse to avoid homosexual partners into an impulse to condemn homosexuality. At least since biblical times homophobic sentiments have been translated into laws that punish homosexuals with death or mutilation, especially in Christian and Muslim kingdoms and their former colonies. A chilling 20th-century example was the targeting of homosexuals for elimination during the Holocaust.

Today homosexuality has been legalized in almost 120 countries, though laws against it remain on the books of another 80, mostly in Africa, the Caribbean, Oceania, and the Islamic world. Worse, homosexuality is punishable by death in Mauritania, Saudi Arabia, Sudan, Yemen, parts of Nigeria, parts of Somalia, and all of Iran (despite, according to Mahmoud Ahmadinejad, not existing in that country). But the pressure is on. Every human rights organization considers the criminalization of homosexuality to be a human rights violation, and in 2008 in the UN General Assembly, 66 countries endorsed a declaration urging that all such laws be repealed. In a statement endorsing the declaration, Navanethem Pillay, the UN High Commissioner for Human Rights, wrote, "The principle of universality admits no exception. Human rights truly are the birthright of all human beings."

During the Enlightenment, the questioning of any moral precept that was based on visceral impulse or religious dogma led to a new look at homosexuality. Montesquieu and Voltaire argued that homosexuality should be decriminalized, though they didn't go so far as to say that it was morally acceptable. In 1785 Jeremy Bentham took the next step. Using utilitarian reasoning, which equates morality with whatever brings the greatest good to the greatest number, Bentham argued that there is nothing immoral about homosexual acts because they make no one worse off. Homosexuality was legalized in France after the Revolution, and in a smattering of other countries in the ensuing decades, as figure 7-23 shows. The movement picked up in the middle of the 20th century and blasted off in the 1970s and 1990s, as the gay rights movement was fueled by the ideal of human rights.

Sources: Ottosson, 2006, 2009. Dates for an additional seven countries (Timor-Leste, Surinam, Chad, Belarus, Fiji, Nepal, and Nicaragua) were obtained from "LBGT Rights by Country or Territory," http://en. wikipedia. org/wiki/LGBT_rights. Dates for an additional thirty-six countries that currently allow homosexuality are not listed in either source.

FIGURE 7-23: Time line for the decriminalization of homosexuality, United States and world

The same graph shows that the decriminalization of homosexuality began later in the United States. As late as 1969, homosexuality was illegal in every state but Illinois, and municipal police would often relieve their boredom on a slow night by raiding a gay hangout and dispersing or arresting the patrons, sometimes with the help of billy clubs. But in 1969 a raid of the Stonewall Inn, a gay dance club in Greenwich Village, set off three days of rioting in protest and galvanized gay communities throughout the country to work to repeal laws that criminalized homosexuality or discriminated against homosexuals. Within a dozen years almost half of American states had decriminalized homosexuality. In 2003, following another burst of decriminalizations, the Supreme Court overturned an antisodomy statute in Texas and ruled that all such laws were unconstitutional. In the majority opinion, Justice Anthony Kennedy invoked the principle of personal autonomy and the indefensibility of using government power to enforce religious belief and traditional customs:

Between the first burst of legalization in the 1970s and the collapse of the remaining laws a decade and a half later, Americans' attitudes toward homosexuality underwent a sea change. The rise of AIDS in the 1980s mobilized gay activist groups and led many celebrities to come out of the closet, while others were outed posthumously. They included the actors John Gielgud and Rock Hudson, the singers Elton John and George Michael, the fashion designers Perry Ellis, Roy Halston, and Yves Saint Laurent, the athletes Billie Jean King and Greg Louganis, and the comedians Ellen DeGeneres and Rosie O'Donnell. Popular entertainers such as k. d. lang, Freddie Mercury, and Boy George flaunted gay personas, and playwrights such as Harvey Fierstein and Tony Kushner wrote about AIDS and other gay themes in popular plays and movies. Lovable gay characters began to appear in romantic comedies and in sitcoms such as Will and Grace and Ellen, and an acceptance of homosexuality among heterosexuals was increasingly depicted as the norm. As Jerry Seinfeld and George Costanza insisted, "We're not gay!… Not that there's anything wrong with that." As homosexuality was becoming destigmatized, domesticated, and even ennobled, fewer gay people felt the need to keep their sexual orientation hidden. In 1990 my graduate advisor, an eminent psycholinguist and social psychologist who was born in 1925, published an autobiographical essay that began, "When Roger Brown comes out of the closet, the time for courage is past."

Liberty presumes an autonomy of self that includes freedom of thought, belief, expression, and certain intimate conduct… It must be acknowledged, of course, that for centuries there have been powerful voices to condemn homosexual conduct as immoral. The condemnation has been shaped by religious beliefs, conceptions of right and acceptable behavior, and respect for the traditional family… These considerations do not answer the question before us, however. The issue is whether the majority may use the power of the State to enforce these views on the whole society through operation of the criminal law.

The most gay-friendly opinion, and the first to show a decline, was on equal opportunity. After the civil rights movement, a commitment to fairness had become common decency, and Americans were unwilling to accept discrimination against gay people even if they didn't approve of their lifestyle. By the new millennium resistance to equal opportunity had fallen into the zone of crank opinion. Beginning in the late 1980s, the moral judgments began to catch up with the sense of fairness, and more and more Americans were willing to say, "Not that there's anything wrong with that." The headline of a 2008 press release from the Gallup Organization sums up the current national mood: "Americans Evenly Divided on Morality of Homosexuality: However, majority supports legality and acceptance of gay relations."

Americans increasingly felt that gay people were a part of their real and virtual communities, and that made it harder to keep them outside their circle of sympathy. The changes can be seen in the attitudes they revealed to pollsters. Figure 7-24 shows Americans' opinions on whether homosexuality is morally wrong (from two polling organizations), whether it should be legal, and whether gay people should have equal job opportunities. I've plotted the "yeses" for the last two questions upside down, so that low values for all four questions represent the more tolerant response.

FIGURE 7-24: Intolerance of homosexuality in the United States, 1973-2010

Liberals are more accepting of homosexuality than conservatives, whites more accepting than blacks, and the secular more tolerant than the religious. But in every sector the trend over time is toward tolerance. Personal familiarity matters: a 2009 Gallup poll showed that the six in ten Americans who have an openly gay friend, relative, or co-worker are more favorable to legalized homosexual relations and to gay marriage than the four in ten who don't. But tolerance is now widespread: even among Americans who have never known a gay person, 62 percent say they would feel comfortable around one.

Sources: Morally wrong (GSS): General Social Survey, http://www. norc. org/GSS+Website. All other questions: Gallup, 2001, 2008, 2010. All data represent "yes" responses; data for the "Equal opportunity" and "Legal" questions are subtracted from 100.

And in the most significant sector of all, the change has been dramatic. Many people have informed me that younger Americans have become homophobic, based on the observation that they use "That's so gay!" as a putdown. But the numbers say otherwise: the younger the respondents, the more accepting they are of homosexuality. Their acceptance, moreover, is morally deeper. Older tolerant respondents have increasingly come down on the "nature" side of the debate on the causes of homosexuality, and naturists are more tolerant than nurturists because they feel that a person cannot be condemned for a trait he never chose. But teens and twenty-somethings are more sympathetic to the nurture explanation and they are more tolerant of homosexuality. The combination suggests that they just find nothing wrong with homosexuality in the first place, so whether gay people can "help it" is beside the point. The attitude is: "Gay? Whatever, dude." Young people, of course, tend to be more liberal than their elders, and it's possible that as they creep up the demographic totem pole they will lose their acceptance of homosexuality. But I doubt it. The acceptance strikes me as a true generational difference, one that this cohort will take with them as they become geriatric. If so, the country will only get increasingly tolerant as their homophobic elders die off.

So tolerance of homosexuality has gone up, and tolerance of antigay violence has gone down. But have the new attitudes and laws caused a downturn in homophobic violence? The mere fact that gay people have become so much more visible, at least in urban, coastal, and university communities, suggests they feel less menaced by an implicit threat of violence. But it's not easy to show that rates of actual violence have changed. Statistics are available only for the years since 1996, when the FBI started to publish data on hate crimes broken down by the motive, the victim, and the nature of the crime. Even these numbers are iffy, because they depend on the willingness of the victims to report a crime and on the local police to categorize it as a hate crime and report it to the FBI. That isn't as much of a problem with homicides, but unfortunately for social scientists (and fortunately for humanity) not that many people are killed because they are gay. Since 1996 the FBI has recorded fewer than 3 antigay homicides a year from among the 17,000 or so that are committed for every other reason. And as best as we can tell, other antigay hate crimes are uncommon as well. In 2008 the chance that a person would be a victim of aggravated assault because of sexual orientation was 3 per 100,000 gay people, whereas the chance that he would be a victim because he was a human being was more than a hundred times higher.

A populace that accepts homosexuality is likely not just to disempower the police and courts from using force against gay people but to empower them to prevent other citizens from using it. A majority of American states, and more than twenty countries, have hate-crime laws that increase the punishment for violence motivated by a person's sexual orientation, race, religion, or gender. Since the 1990s the federal government has been joining them. The most recent escalation came from the Matthew Shepard and James Byrd, Jr., Hate Crimes Prevention Act of 2009, named after a gay student in Wyoming who in 1998 was beaten, tortured, and tied to a fence overnight to die. (The law's other namesake was the African American man who was murdered that year by being dragged behind a truck.)

Source: Data from the annual FBI reports of Hate Crime Statistics (http://www. fbi. gov/hq/cid/civilrights/hate. htm). The number of incidents is divided by the population covered by the agencies reporting the statistics multiplied by 0.03, a common estimate of the incidence of homosexuality in the adult population.

FIGURE 7-25: Antigay hate crimes in the United States, 1996-2008

We don't know whether these odds have gotten smaller over time. Since 1996 there has been no significant change in the incidence of three of the four major kinds of hate crimes against gay people: aggravated assault, simple assault, or homicide (though the homicides are so rare that trends would be meaningless anyway). In figure 7-25 I've plotted the incidence of the remaining category, which has declined, namely intimidation (in which a person is made to feel in danger for his or her personal safety), together with the rate ofof aggravated assault for comparison.

So while we can't say for sure that gay Americans have become safer from assault, we do know they are safer from intimidation, safer from discrimination and moral condemnation, and perhaps most importantly, completely safe from violence from their own government. For the first time in millennia, the citizens of more than half the countries of the world can enjoy that safety -- not enough of them, but a measure of progress from a time in which not even helping to save one's country from defeat in war was enough to keep the government goons away.