Both forms of conservatism can be found in Edmund Burke's Reflections on the French Revolution, so that both metaphysical conservatives and evolutionary conservatives can appeal to Burke. The evolutionary side of Burke's conservatism links him to David Hume and Adam Smith. Darwin's evolutionary theory of morality follows in this tradition of Hume, Smith, and Burke. Now, the new research being done in evolutionary moral psychology by people like Jonathan Haidt is extending and deepening this tradition of evolutionary conservatism.
One can see how Haidt fits into this tradition by noticing how he began a few years ago to recognize the affinity between his moral psychology and evolutionary conservatism. In The Righteous Mind, Haidt identifies "two turning points" in his intellectual life (288-89). The first was his visit to India in 1993, where his mind was opened to "the ethics of community" and "the ethics of divinity" as moral foundations that went beyond "the ethics of autonomy" predominant in Western liberal societies. But even so, he remained a partisan liberal at least until 2008. In the presidential election of 2008, he was initially excited by Barack Obama, because he seemed to be broadening the moral appeal of the Democratic Party to include appeals to patriotism and traditional morality. In his book The Audacity of Hope, Obama seemed to have the "broader moral palate" of "a liberal who understood conservative arguments about the need for order and the value of tradition" (163). But then, by the end of the campaign of 2008, Obama seemed to pull back to the more narrow moral psychology of the liberal Democrat who sees the morality of social justice and equality but not the morality of loyalty, authority, and sanctity.
Expressing his disappointment, Haidt in 2008 wrote "What Makes People Vote Republican" for John Brockman's online salon at Edge.org, which was Haidt's first statement of his argument that conservatives understand the full range of moral psychology, while liberals do not. That's the claim that has stirred so much controversy around Haidt.
Although it is sometimes muted in his writing--because Haidt is still nervous about openly identifying himself as a conservative--his embrace of conservative moral psychology was made possible by the second turning point in his intellectual life--his reading in 2005 of Jerry Z. Muller's book Conservatism (Princeton University Press, 1997). This book is an anthology of conservative writing guided by Muller's argument about what constitutes the core themes of conservative thought.
In his introductory essay, Muller argues that conservatism should be distinguished from orthodoxy and from the counter-Enlightenment. Orthodoxy believes in "a transcendent moral order, to which we ought to try to conform the ways of society," which is Russell Kirk's statement of the "first canon of conservative thought." According to orthodoxy, social order must satisfy some external metaphysical order, which can require radical change. Muller rejects this as deviating from the main line of conservative thought.
And although conservatism is often identified as a reaction against the Enlightenment, Muller argues that modern conservatism actually arose as a movement within the Enlightenment, and particularly in the work of those like David Hume, who offered an empirical science of social order that was contrary to the utopian rationalism of some Enlightenment thinking.
Muller's crucial move here is in taking Hume as his model conservative and then stressing those strands of Burke's thought that conform to Hume's empirical and evolutionary conservatism, which is the tradition of conservative thought that I defend in my Intercollegiate Review article.
One should notice that this is a very liberal conservatism, as contrasted with the illiberal conservatism of conservative theocracy as espoused by those like Louis de Bonald and Joseph de Maistre. Generally, American conservatives have been liberal conservatives, because the American political tradition has been predominantly liberal (as Louis Hartz argued).
While traditionalist conservatives like Kirk can sound like theocratic conservatives when they affirm that social order must be derived from the law of God, even they turn out to be liberal conservatives, because they accept the liberal arguments for separating Church and State, for religious toleration, for democratic government, for free markets, and for moral pluralism. As is well argued by Mark Henrie, liberal conservatives want to "box in liberalism" by promoting "the intermediate associational life of society" as a social realm for moral character formation that stands between the public realm of government and the private realm of individual life (Henrie, "Understanding Traditionalist Conservatism,' in Peter Berkowitz, ed., Varieties of Conservatism in America [Stanford, CA: Hoover Institution Press, 2004], 3-30). This corresponds to what Haidt says about how the groupish or hiving psychology of human beings can be expressed in a nation that is "full of small-scale hives," so that "many moral matrices coexist within each nation" (107, 110, 242-43). Thus, the individual liberty of the liberal Gesellschaft (contractual society) can be combined with the moral community of the conservative Gemeinschaft (organic society).
In The Righteous Mind, Haidt indicates the crucial importance for him in seeing Muller's version of the evolutionary conservatism that began with Hume. He writes:
As a lifelong liberal, I had assumed that conservatism = orthodoxy = religion = faith = rejection of science. It followed, therefore, that as an atheist and a scientist, I was obligated to be a liberal. But Muller asserted that modern conservatism is really about creating the best possible society, the one that brings about the greatest happiness given local circumstances. Could it be? Was there a kind of conservatism that could compete against liberalism in the court of social science? Might conservatives have a better formula for how to create a healthy, happy society?I should emphasize that although Haidt is an atheist and is therefore suspicious of religious orthodoxy, he recognizes the importance of religious belief as an evolved tendency of the human species for supporting social cooperation by sacralizing moral norms. Haidt even doubts that a healthy society of atheists is possible (269).
I kept reading. Muller went through a series of claims about human nature and institutions, which he said are the core beliefs of conservatism. Conservatives believe that people are inherently imperfect and are prone to act badly when all constraints and accountability are removed (yes, I thought; see Glaucon, Tetlock, and Ariely in chapter 4). Our reasoning is flawed and prone to overconfidence, so it's dangerous to construct theories based on pure reason, unconstrained by intuition and historical experience (yes; see Hume in chapter 2 and Baron-Cohen on systemizing in chapter 6). Institutions emerge gradually as social facts, which we then respect and even sacralize, but if we strip these institutions of authority and treat them as arbitrary contrivances that exist only for our benefit, we render them less effective. We then expose ourselves to increased anomie and social disorder (yes; see Durkheim in chapters 8 and 11).
Based on my own research, I had no choice but to agree with these conservative claims. As I continued to read the writing of conservative intellectuals, from Edmund Burke in the eighteenth century through Friedrich Hayek and Thomas Sowell in the twentieth, I began to see that they had attained a crucial insight into the sociology of morality that I had never encountered before. They understood the importance of what I'll call moral capital. (Please note that I am praising conservative intellectuals, not the Republican Party.) (289-90)
Here again, Haidt follows in the tradition of evolutionary conservatism, which recognizes that human beings are religious animals by nature, and that religion can be important in binding people together into groups. Thus, religion has a practical truth (in its social utility) regardless of whether one is persuaded of its doctrinal truth. Evolutionary conservatism accepts the irresolvability of the reason-revelation debate, in which neither side can refute the other. This explains Haidt's disagreement with the "New Atheists" (Sam Harris, Richard Dawkins, Daniel Dennett, Christopher Hitchens) who deny that religion serves any evolutionary adaptive function (249-69).
Some posts on related themes can be found here, here, here, and here.