Darwin and his progeny have traced human ethics to evolved traits, especially empathy and compassion, that help individuals survive and procreate within social groups. The idea that natural selection confers advantages on groups as well has gradually gained scientific support. This leaves many questions unanswered, however, because cultures powerfully shape whatever emotional and ethical predispositions we inherit.
Consequently, there is significant variability in what people consider good and bad behavior. Moreover, for cultural creatures like us, who consciously and unconsciously transform the places we inhabit, and thus, the evolutionary process itself, ethical perceptions and beliefs will continue to be in flux. Put simply, we are biocultural creatures who are shaping and being shaped by our ethical mores and related behaviors. And these mores are a complex mix of emotions and understandings regarding the way the world has come to be and the way it works. Ethical mores tend to evolve in ways that enhance survival and reproductive success, and if not, they will eventually be teased out of the genome.
Many have plausibly argued that as human groups become larger and more interconnected, natural selection favors those who develop positive feelings toward others and cooperative mores. Not uncommonly, some part of this is also the result of an evolved brain capable of analyzing the perils of violence and the advantages of cooperation and even altruism.
Sometimes we also extend our moral sentiments beyond our own species. Humans often have fondness for and felt obligations to the domestic animals we raise to eat, make our lives easier, and keep us company. Indeed, we have co-evolved with many organisms and sometimes have mutually dependent relationships with them, as exemplified by collaborations between canine and human hunters. Domesticated animals are the organisms with whom we have most often established mores that constrain our behavior. These norms are often expressed in religious prohibitions, conveyed orally and in sacred texts. Humans have been and often are still hostile to wild animals, however, whom many of our kind consider competitors or predatory threats. And we are often indifferent to organisms with whom we have little contact.
So how far can sympathy extend? Can it reach predators and prey, flora and fauna, otters and oysters?
How far we extend our sympathies is informed by our understanding of the ways of the world. To use an anthropocentric example, as the science of same-sex attraction spread, so did sympathy for the LGBT community. This is entirely logical because, as Kant explained when arguing that human beings have moral freedom, to say someone ought to do something assumes the prescribed action can be done. Actions that are beyond choice cannot be moral issues. Facts matter—in this case, the biology of eros is ethically decisive for those who accept consensus science.
Facts matter as well when considering the implications of the evolutionary and ecological sciences for human moral evolution.
There is tantalizing evidence that, wherever human understandings of the way the world came to be and how it works are informed by science, increasing numbers of people extend their sympathies and obligations beyond their own kind to other species and entire environmental systems.
One aspect of this trend I will quickly dispatch, assuming for many readers this is already obvious: that the wellbeing of humans and their social systems is dependent on the diversity, fecundity, and resilience of Earth’s environmental systems.
With such an understanding, on a purely prudential basis, many of us have taken up the environmental cause, recognizing that our own wellbeing and the wellbeing of those we love, requires conservation of the environmental systems upon which our social systems, and our lives, depend. This is a logical deduction straight from the science of ecological interdependence.
Perhaps less obvious are the ways that evolutionary science leads to an understanding of biological kinship. This perception of kinship, in turn, often leads to ethics ascribing intrinsic value to nature; value apart from its usefulness to us.
Early during his lifework, Charles Darwin took a leap of moral imagination that hinted at such an ethics:
If we choose to let conjecture run wild, then animals, our fellow brethren in pain, diseases, death, suffering and famine—our slaves in the most laborious works, our companions in our amusements—they may partake [of] our origin in one common ancestor—we may be all netted together.
Perhaps reticent to make too strong a statement, here, Darwin suggested we “let conjecture run wild”—but this requires, as the rest of the passage makes clear, that we empathize with the suffering and struggle for existence of other animals. Then, adding the critically important notion that we share a common ancestor—which it is now clear we share with all living things—Darwin pointed toward recognition of biological kinship. This he then wed in the final line to a metaphorical statement of ecological interdependence.
Subsequently, many others have had related insights.
John Muir wrote of experiences in nature that made him feel “part of wild nature, kin to everything.”
Albert Schweitzer’s “ethics of reverence for life,” for example, was rooted in feelings of belonging to the earth and humility about humanity’s tiny place in the universe, and in empathy for and solidarity with all creatures, with whom we share a will-to-live: “The essential thing to realize about ethics is that it is the very manifestation of our will-to-live,” Schweitzer wrote. He concluded, goodness “is the saving or helping of life, the enabling of whatever life I can to attain its highest development.”
Rachel Carson expressed her affinity with Schweitzer’s reverence-for-life ethic when in 1962 she dedicated Silent Spring to him. But in 1954, when speaking to a group of female journalists, she hinted at an evolutionary root for the love of nature. “This affinity of the human spirit for the earth and its beauties is deeply and logically rooted,” Carson wrote, because “as human beings, we are part of the whole stream of life.” In this, she anticipated the biophilia hypothesis that Edward O. Wilson advanced a generation later, which theorized that the affective connections human beings have for their natural surrounds have evolutionary roots and an adaptive function.
No one has drawn out the ethical implications of evolutionary science more insightfully than Aldo Leopold. In A Sand County Almanac, he stressed that ethics is a process of social evolution that is an “intellectual as well as emotional process.” Such ethics recognize that “the individual is a member of a community of interdependent parts,” which should lead to humility, understanding one’s self as “plain member and citizen” of the world, as well as a corresponding precautionary approach, and even, “love, respect, and admiration” for nature. And Leopold drew directly on Darwin when expressing a kinship ethics that understands that all organisms share a common ancestor:
It is a century now since Darwin gave us the first glimpse of the origin of species. We know now what was unknown to all the preceding caravan of generations: that men are only fellow-voyagers with other creatures in the odyssey of evolution. This new knowledge should have given us . . . a sense of kinship with fellow-creatures; a wish to live and let live; a sense of wonder over . . . the biotic enterprise.
This kinship ethic, expressed almost mythically, resembles the empathy Schweitzer felt toward all who, like us, struggle to survive and flourish. It suggests, whatever else our ethics may enjoin, that to the greatest extent possible, moral and empathetic creatures should get out of the way of the survival quest of others.
Of course, ethics rooted in understandings of interdependence and biological kinship leave unanswered many moral questions.
One obvious example is that every organism survives by eating their relatives, and not always distant ones! Consequently, if ethics are grounded in knowledge of biological kinship and corresponding moral sympathies, then how and whom to eat can be a vexing conundrum.
To take such musing further, evolutionary ethics understands why we feel our deepest obligations to our closest relatives. Because this helps to explain how we got here and why we are still here, we should respect these feelings and the priorities that correspond to them. But it does not follow that because we honor such priorities, we have no responsibilities to our distant relatives (human and other kind). We properly care for our closest relatives personally and for distant ones through collective action, including political engagements. There is no obstacle to kinship ethics as a basis for caring about the entire web of life.
And returning to the question of whom to eat, since all organisms must eat and few can survive without ending the life of others, there is no universally compelling moral objection to ending life to maintain life. So Leopold’s maxim to act in a way that respects the biotic community, which does not focus on individual lives exclusively, is a reasonable, fact-based approach. This certainly means placing a high priority on preserving Earth’s biological diversity. To this we need a modest update of Leopold’s maxim, dictated by contemporary climate science, a prescription to respect the entire biosphere, its precious, safeguarding atmosphere included.
Although there are many details to work out when weighing specific ethical choices, an ecological and evolutionary worldview leads quite logically to a commitment to discern and pursue social arrangements that promote flourishing and resilient biocultural systems. Such understandings tend to drive a salutary humility in that difficult quest. Humility in turn provides a basis for reasoned discussion and cooperation, and thus, a prospect for further moral evolution.
 I provide a global tour of this evidence in Dark Green Religion: Nature Spirituality and the Planetary Future (University of California Press, 2010).
 From his Notebooks on Transmutation, cited by Donald Worster, 1994 , Nature's economy: a history of ecological ideas. second ed. Cambridge, MA: Cambridge University Press.1994 : 180).
 In Michael P. Cohen, The Pathless Way: John Muir and American Wilderness. Madison: University of Wisconsin Press, 1984, 359.
 The full passage from this last quote is evocative, “What shall be my attitude toward this other life? It can only be of a piece with my attitude towards my own life. If I am a thinking being, I must regard other life than my own with equal reverence. For I shall know that it longs for fulness (sic) and development as deeply as I do myself. Therefore, I see that evil is what annihilates, hampers, or hinders life. And this holds good whether I regard it physically or spiritually. Goodness, by the same token, is the saving or helping of life, the enabling of whatever life I can to attain its highest development.” These quotes are from Albert Schweitzer’s 1936 article "The ethics of reverence for life,” Christendom 1:225-239, which is available at http://www1.chapman.edu/schweitzer/sch.reading4.html.
 This quote is from one of the most illuminating passages of Carson’s spirituality and ethics. It was posthumously published in Lost Woods: The Discovered Writing of Rachel Carson (ed. Linda Lear). Boston: Beacon Press, 1998, 148-163 (in text, 160). The talk was titled “The real world around us” and the full paragraph in which the in-text quote appears is highly illuminating “I believe this affinity of the human spirit for the earth and its beauties is deeply and logically rooted. As human beings, we are part of the whole stream of life. We have been human beings for perhaps a million years. But life itself—passes on something of itself to other life – that mysterious entity that moves and is aware of itself and its surroundings, and so is distinguished from rocks or senseless clay—[from which] life arose many hundreds of millions of years ago. Since then it has developed, struggled, adapted itself to its surroundings, evolved an infinite number of forms. But its living protoplasm is built of the same elements as air, water, and rock. To these the mysterious spark of life was added. Our origins are of the earth. And so there is in us a deeply seated response to the natural universe, which is part of our humanity.”
 See Edward O. Wilson, 1984 Biophilia, Cambridge, Mass.: Harvard University Press, and Stephen Kellert, and E. O. Wilson, eds., 1993, The biophilia hypothesis. Washington, D.C.: Island Press.
 Aldo Leopold, 1966 . A Sand County almanac with essays on conservation from Round River (enlarged ed). New York: Sierra Club and Ballantine Books. In-text Leopold quotes in order appear on pages, 263, 239, 240, 261, 16–17. The original publication of A Sand County Almanac was in 1949 by Oxford University Press. Other scientists have deduced a kinship ethics from their evolutionary understandings. Biologist E.O. Wilson, for example, wrote: “We are literally kin to other organisms. [Our differences] are only a matter of degree, measured in small steps as gradually enlarging magnitude of base-paired differences in DNA.” Edward O. Wilson, Biophilia. Cambridge, Mass.: Harvard University Press, 1984, 130. Wilson cited Gordon Burghardt and Harold A. Herzog, Jr. 1980. "Beyond Conspecifics: Is Brer Rabbit Our Brother?" BioScience 30 (11, 1980):763-768. Conservation biologist Michael Soulé wrote: “There is now no question that all life on earth evolved from a common ancestor. The genetic material and the codes embedded within it reveal that every living kind of plant and animal owes its existence to a single-celled ancestor that evolved some three and a half billion years ago. All species are kin.” Herein “The Social Siege of Nature,” in Reinventing Nature? Responses to Postmodern Deconstruction, eds. M. Soulé and G. Lease, 137-70 (here 141-42). San Francisco: Island Press, 1995. Philosopher Baird Callicott quoted Soulé statement and repeated the basic argument "the idea that all extant species, including Homo sapiens, are descended from one Urform or from very few such forms is not in doubt. Hence, human beings are a part of nature, and we are kin--literally, though more or less distantly kin--to all other kinds of life." J. Baird Callicott, "Do deconstructive ecology and sociobiology undermine Leopold's Land Ethic?" Environmental Ethics 18 (1996, #4): 362. Although there are ethical differences among those who recognize biological kinship there is agreement this is morally significant.
 There are many examples wherein people, scientists and non-scientists alike, view scientific cosmogonies as having mythic resonance and ethical implications. For one example, E. O. Wilson used the phrase “Epic of Evolution” in 1978 and called evolution “the best myth we will ever have” Quoted in Connie Barlow, 1998. "Evolution and the AAAS: a leading scientific organization considers religious interpretations and the cultural importance of modern scientific cosmology." Science and Spirit 9 (1):12-13, here 12. citing (without pagination) E.O. Wilson, 1978, On human nature. Cambridge: Harvard University Press.
This graphic, published by conservation biologist Reed Noss, illustrates the way ethics have evolved over time to embrace wider circles of life. Reed F. Noss, 1992. “Issues of scale in conservation biology,” in P.L. Fiedler and S.K. Jain, eds. Conservation Biology: The Theory and Practice of Nature Conservation, Preservation, and Management. Chapman and Hall, New York, 1992, Pages 239-250). A similar graphic was published in 1989 by Roderick Nash in The rights of nature: a history of environmental ethics. Madison: The University of Wisconsin Press, 1989, p. 7. And in his study of changing ecological paradigms historian Donald Worster concluded that for those who derive their worldviews in science rather than religion, “there is really no place to go but nature” for moral guidance; he then suggested that understandings of ecological interdependence provide an excellent starting place. Nature's economy: a history of ecological ideas (second ed. Cambridge, MA: Cambridge University Press, 1994 ), p 337. These three examples provide further evidence that many are indeed using ecological and evolutionary science as starting points for both understanding moral evolution and advancing recent ethical suppositions based upon such understandings.
Image credit:The Harvest at Montfoucault 2 by Camille Pissarro. Courtesy of Art Gallery ErgsArt / Flickr.