What creates political and social changes in a democracy? This is a question being asked a lot lately in the United States, largely because the degree of polarization of American politics is widely perceived to have increased dramatically since the 1960s, with each party becoming less tolerant of ideological diversity in its ranks and both parties therefore finding it harder to compromise during the actual process of governing.

Despite today’s gridlock, it is clear that there is social and political change over time. One need only look at an old movie or watch an episode of the TV series “Mad Men” to realize the immense changes in social attitudes that have taken place in the United States over the past several decades. As it turns out, evolutionary science has a lot to say about this paradox and provides useful insights as to the process and the time scale that will likely be required to break the current political gridlock.

First of all, we know that there are predispositions for certain political points of view that are rooted in personality types (which are analogous to a biological genotype), but they are predispositions that will manifest themselves in differing ways depending on circumstances. For example, in the United States, people who are predisposed to highly value compassion will almost certainly be political liberals, and those who most highly value individual autonomy and responsibility will almost certainly become conservatives. The underlying personality types are present in all societies over time, but their proportions can vary to some extent in a manner analogous to an epigenetic expression, as events that occur in a society during a generation’s formative years tend to leave an indelible mark on lifelong political views. For a detailed exploration of exactly how this mechanism works in practice, see Jon Haidt’s current book The Righteous Mind.

In a democratic society, the result is that there are, for example, always liberals and conservatives, but the mix can shift, even though there are probably irreducible minima of each type. So, in the 1960’s, the Vietnam War and the counterculture produced two groups in the Baby Boomer generation, one that embraced their inner hippie and a distrust of authority, and one that was appalled at the threats to society that they saw in the “turn on, tune in and drop out” lifestyle. The cultural battles that played out over the following decades in the political arena between these two different perceptions are clearly one reason that it is so hard to find compromise between the groups as their members try to function as adult political leaders.

This kind of historical, generational “lock-in” of political attitudes is reflected in American political scientists’ observations that there are periodic “wave” elections in the United States that break with past patterns and result in new, stable patterns of voting. Political attitudes that are crystallized in such elections tend to be quite impervious to near-term subsequent disruption. By way of example, FDR’s election in 1932 ushered in a Democratic dominance of Presidential elections that ended only in 1968.

It also seems very clear that there are important effects of group identification that influence how the ideological “genotypes” in a society react to events. David Hackett Fisher’s book Albion’s Seed traces how the various waves of emigration from culturally different parts of England still influence the culture of their descendants today, including their politics. The so-called Scots-Irish, for example, brought anti-authoritarian and military traditions with them that had been forged by generations of living in the relatively lawless border between Scotland and England and in the unstable Plantation of Ulster experiment. These traditions live on, particularly in the mountainous parts of the South, and make their descendants even now disproportionately the source of American military recruits. Likewise, there is no doubt that African-American political attitudes differ sharply from American society as a whole, attributable to the very different life in the United States that people of color, especially those descended from slave immigrants, have experienced.

So, how does change happen? It is clearly not the result of changes of heart among large numbers of adults during an election. Political arguments are poor dinner table topics because, like religion, they are more likely to trigger intense arguments rather than camaraderie if the participants are not already, as we say, “like-minded.”  Likewise, most political arguments when a society is polarized are about energizing one’s base rather than reaching out to the other side. There is a reason that people seek political conversations that reinforce their views rather than challenge them. Fox News and its liberal counterparts provide comfort and talking points to their audiences, and sometimes wholly different versions of the facts when needed to reinforce those views.

Instead, it seems clear that the political consensus of the public at any moment is a complex result of the basic predispositions of its citizens, mediated by experiences, with the cumulative effects of the specific experiences of its cohesive groups driving the mix. In this regard, it is a very typical evolutionary outcome, where a population can be quite adaptive even though individuals are not. It is reassuring that American political institutions seem to be well enough designed to have accommodated profound changes in the underlying society while providing continuity. The timetable can be long, but change does happen, in a pattern that looks suggestively like other forms of cultural evolution, continuously but sometimes faster and sometimes slower.