Thursday marks the bicentennial of Charles Darwin and Abraham Lincoln’s birth. Different though they and their influences were, both contributed to a tectonic shift in ideas. Neither arrived at his culminating treatise: Darwin’s 1859 The Origin of Species and Lincoln’s 1865 Emancipation Proclamation in a vacuum. Both drew upon and subsequently enlarged, crystallized and codified pre-existing ideas. Lincoln predicated his decision to end U.S. slavery on the existing framework of abolition built by many, and established in Britain in 1833, through tireless efforts of William Wilberforce. Darwin applied his keen observation and synthesis to the work of Alfred Russel Wallace who "had developed an evolution theory similar to Darwin’s but not as fully substantiated." 
These two men each in their own way demonstrate the evolution of ideas, underscoring that part of the evolutionary process, at least for humans, involves reckoning with tectonic ethical and intellectual shifts.
I am struck by this as I read the "My Turn" guest essay in this week’s Newsweek, penned by Richard Mouw, the president of Fuller Theological Seminary in Pasadena, California. Fuller, an evangelical Christian writes of himself, "I have spent several decades of my life trying to spell out and evangelical alternative to ‘the worst kind of fundamentalism.’ My friends and I have argued that the Bible supports racial justice, gender equality, peacemaking and care for the environment—views that often draw the ire from the worst kind of fundamentalists."  Mouw writes of his desire for respectful dialogue about Proposition 8, the recently passed ban on same-sex marriage in California. He supported the ban and fears its passage would lead to a "slippery slope." If we as a nation, in his words, "normalize" gay marriage, "what would keep us from extending marriage to a three-partner arrangement?"
During the four years I lived in Canada where same-sex marriage is legal, I officiated close to two dozen ceremonies. No one approached me about a three-partner marriage, but to be fair to Mr. Mouw’s concerns, there is a small group within Unitarian Universalism advocating for polyamory, which denotes a loving domestic relationship among more than two people. Admittedly, when I first spotted an ad in the UU World for a polyamorous organization, I cringed, along with several of my colleagues. Immediately I thought, oy, how will we achieve respect from other denominations if we always house the fringe elements?
But the truth is, for me, that I wouldn’t be standing here if it weren’t for the fringe elements who paved my way. While there are slightly more female than male UU ministers serving congregations today, that was not the case fifty years ago. And while I joke sometimes at UU minister gatherings that middle-aged women sporting comfortable shoes have taken over, I am indebted both to those who came before, and the congregants now who care not, or perhaps appreciate, a female minister who finds her authentic fashion expression largely in the men’s department.
As for polyamory, I found having one domestic partner challenging enough. I am one of those folks genuinely happiest living as a single person sustained by friendships, family, and work I love. For me, that is enough. But I appreciate the deep satisfaction and enrichment many people, gay and straight, find within marriage. The hopefulness, devotion and delight I witnessed among gay couples perhaps exceeded that of the heterosexual couples whose weddings I presided over, precisely because the same-gender pairs who could finally marry legally in Canada, came to it with such appreciation for the sanctity of the commitment and the communal recognition marriage brings. This is not to say, sadly, that two of the lesbian couples are already divorced. It is only to say that an idea that was unimaginable fifty or even twenty years ago, has already entered the public imagination, and as my learned and wise mentor Bishop John Shelby Spong told me, "Once something like gay marriage enters the public discourse it is only a matter of time until it becomes a reality."
So to Mr. Mouw, I can only suggest that part of our process of evolution is the flourishing of ideas, some of which, like species, will meet extinction quicker than others. Obviously, polygamy existed during the centuries known as "Biblical times," for it appears in several biblical texts. Obviously homosexuality existed as well. Otherwise the author(s) of the books of Exodus and Leviticus, nor the Apostle Paul would not have felt compelled to denounce it. Homosexuality occurs naturally in about ten percent of the human population and pops up in various other species as well. For thousands of years, some men have opted to have multiple wives, and in a few cultures, women have chosen multiple husbands. Were I to delve into anthropological research I would probably find some basis for multiple partners as a mechanism for increasing the likelihood of children, and the attainment of property, land, and status. Today’s polyamorous UUs may seek something else: a broader base of intimacy; more adults to parent or share household responsibilities, or even something as mundane as loving, desiring two people at once.
If we pull back our lens to consider contemporary relational patterns in evolutionary time, this century with its ongoing conversation and political struggle about same-gender marriage, comprises a nanosecond of geologic time. With roughly six billion human inhabitants, the earth groans under the expectation that it support us at the same time we deplete what we perceive as resources for our taking. Even if every same-gender couple seeking legal matrimony were to marry this year, and even if the pocket of polyamorous UUs could do the same (though I have no idea whether any of them would wish to), we as a species, and even as a subset of inhabitants of industrialized nations where polygamy and polyandry are illegal, probably would not experience a shift of tectonic proportion.
To our evangelical brothers and sisters who genuinely worry over human behavior they view as falling outside the scope of Biblical teaching, I extend compassion because it cannot be easy to try to live ethically and non-hypocritically within the constraint of a literalist reading of texts that normalize polygamy and slavery, smiting entire communities and individual punishments so severe it would be hard to honor and employ either our God-given or evolutionarily-endowed capacity for reason and abstract thought.
I don’t say this smugly. To be a person of devout faith struggling to live in accordance with one’s religious understanding describes me. In this way I have it easier: as a Unitarian Universalist, and as someone raised in a Reform Jewish home, I have never been saddled with literalism or a fundamentalism that declares me, my religious forebears, or fellow adherents the sole purveyor of truth.
That means as I, and we, enter the great evolution of ideas, we bring to process not just the capacity but the predisposition to engage openly: to wade into the river, not to stand on its banks and assume we can direct its way. If we build a dam with our bodies we may redirect the flow—temporarily—but we cannot insist or insure that the next generation who replace us as we tire or die, will choose to dam the river in the same way.
In the centuries the various books of the Bible were written, marriage laws did not exist. The laws we recognize began as property rights for men. Few contemporary women would seek to enter into marriage as a covenant designed to clarify and insure a husband’s right to her value and that of her possessions or land. The evolution of our idea of what marriage means has shifted radically in the last fifty years, and in the hundred before that. Faster than the blink of a geological eye.
For forty years between 1932 and 1972, the U.S. Public Health Service (PHS) conducted an experiment on 399 black men in the late stages of syphilis. These men, for the most part illiterate sharecroppers from one of the poorest counties in Alabama, were never told what disease they were suffering from or of its seriousness. Informed that they were being treated for "bad blood," their doctors had no intention of curing them of syphilis at all. 
Today, thirty-seven years later, the scientific community hangs its collective head in shame, or should. New standards are in place. And while today’s public conversation about the ethics of primates and other mammals in scientific research may sound like people on the fringe, forty years ago, there had to have been some folks somewhere saying it is not acceptable that the United States Public Health Department lied to economically disadvantaged African American citizens to benefit more prosperous white ones.
Forty years from now, there may be a shift in collective sentiment. We may not publicly tolerate the use of animals in experimentation. We may not tolerate massive feed lots or the aerial killing of wolves. A hundred years hence, our children’s children and their children may shudder at our barbarism. Fists and voices raised over the legality of same-gender marriage may seem passé.
Fifty or a hundred years from now, a sizeable number of people will still consult a sacred text: the Bible, the Qu’ran, the Bhagavad Gita, the Tao Te Ching. the Diamond Sutra for guidance on right, and right-sized relations.
Because we never step in the same river twice, our descendents will likely arrive at different and differing answers.
In the 19th and early twentieth century when it was commonplace for impresarios and clinicians to place human beings with deformities or variations on view, few expressed outrage; many more paid to glimpse the display. Sideshows and so-called scientific displays of live human subjects are illegal, and those that might remain do so as remnants on the fringes of what the majority consider unethical. Still, a foray into the netherworld of cyberspace would undoubtably yield a trove of contemporary images.
Though this generation distances itself from the pseudo-science of the Third Reich with its racist applications of craniometry and eugenics. "In 1950, UNESCO issued a statement signed by leading researchers debunk[ing] race theories,"  yet tragically, that has not put an end to racism or theories of cultural superiority among many of the world’s people.
What has changed is the emergence of a palpable shift in thinking. What previously functioned as viable intellectual currency has become the counterfeit bill of our day. In the same way forgery exists, at least most of us recognize it as such.
But that recognition emerges with time as both context and sensibilities change.
In early 2009, at the bicentennial of Darwin and Lincoln’s birth, same-gender marriage, reproductive technology, animal rights stand like boulders in the river of ideas. Well-intentioned people of varying perspectives wade into the river—some trying to dislodge the stones and send them hurtling downstream out of view; some working to transform the rocks of impasse into the sands that form the riverbed of common thought.
A hundred and fifty years after Darwin published The Origin of Species his theories hold—among most, but not all. A hundred and four, almost five years after Lincoln signed the Emancipation Proclamation the first African American President occupies the White House—to the delight of perhaps billions, and to the horror of white supremacists and apparently Rush Limbaugh. As tempting as it may be for religious liberals to shake our heads with incredulity at biblical literalism, Creationism, the strident opposition to same-gender marriage, and perhaps most of all, at the enormous following and political sway Rush Limbaugh has amassed, we can with humility recall, as the great African American scholar Henry Louis Gates reminds us, Lincoln, even though he opposed slavery, considered "the Negro" intellectually inferior, unsuitable to serve in the military or marry a white person.
How, we might wonder, could someone who progressively changed history, be drawn into the undertow?
Our evolution as humans, as Lincoln and Darwin so poignantly and eloquently demonstrate, entails the evolution of ideas: not just thoughts, but critical and compassionate thinking, the ability to investigate, weigh, and synthesize multiple perspectives and contexts. The variations—of species and within our own—promise and demand nothing less.