Watching old movies, it is easy to be shocked by all the gratuitous touching. By “old” I mean anything recorded before March 2020, when people were still squeezing past each other to get to the bar, exchanging grimy coins and passing drinks back with their dirty bare hands. Did we really throng like that?

It is a measure of how well we have internalised the reason for staying apart that casual, pre-coronavirus intimacy looks so alien. When we cringe at an old photo of ourselves with bad hair or clothes (or both, in my case) it is because we apply the lens of new information to judge our naive former selves. And now a whole world of slack hygiene feels remote in that sepia-tinted way; not just in time, but in values.

The change is cultural, not political, and will not be undone by government decree. Even when some shops are allowed to trade or schools partially reopen, the duty to be distant will remain for as long as contagion is a risk. In the absence of a vaccine, that risk is open-ended. It will be a while before strangers shake hands again. Maybe the habit will be lost.

This is not a superficial aspect of the Covid-19 crisis. Societies are shaped by custom and ritual as much as they are held together by legislation. There is no law against queue-barging, for example, but British people still have a keenly developed sense of justice around the issue.

We must not underestimate the aggregate effect of curtailing millions upon millions of micro-niceties, even if we cannot predict what the impact will be. After the rules of lockdown are eased, the cordon sanitaire will remain in our minds. Each handshake or shared bag of chips is a little social contract – a declaration of affinity. And without physical proximity we have to work harder to negotiate those alliances.

It isn’t hard to see how our species evolved this way. There is an obvious cost in admitting predators and enemies into our personal space, so we are hard-wired to associate social distance with suspicion. The same applies in the case of hygiene, where we have evolved what the psychologist Mark Schaller has called a “behavioural immune system”. At an individual level that is the spasm of recoil from a foul smell. At a more complex level it informs antisocial human characteristics – wariness of all things unfamiliar, especially people from outside our immediate, trusted circle.

Evolutionary biologists have observed a cross-cultural and historical correlation between the prevalence of infectious disease and authoritarian politics. The theory posits that “pathogen stress” leads to a more aggressive behavioural immune response, making societies less open, less tolerant and readier to sacrifice liberties for collective protection.

That might sound like a wild extrapolation from two-metre gaps at the supermarket checkout. I don’t think lockdown will activate some dormant genetic predisposition to tyranny. The opposite response feels closer to the surface – our pent-up social energies one day exploding on to the streets in a licentious touchy-feely carnival.

But that release might be further away than we hope. Meanwhile, it doesn’t take an evolutionary biologist to hypothesise that chronic insecurity ploughs fertile ground for toxic politics. That is a lesson from the rise of xenophobic nationalism across Europe and the Americas in the decade since the last financial crisis, amply corroborated by evidence from the first half of the 20th century.

History is not destiny, so it is reasonable to presume that 21st century societies will find innovative ways to manifest the consequences of mass anxiety. For a start, we have the digital infrastructure that means a lot of life in lockdown has migrated online. That journey is keeping many of us in financial solvency and mental equilibrium, but with an insidious cost in social cohesion. Before coronavirus, people were already burrowing into digital silos, selecting the information that suited their prejudices or having that information selected for them by algorithms that interpreted prejudices from their search history.

Social media is a brilliant centrifuge, separating us into discrete cultural channels, and an efficient engine for radicalisation, polarisation and paranoia within those channels. Shared attitudes are refined; the grit of contradictory evidence is expelled; moderates fall silent while members of the group bid each other up towards the most extreme iteration of any opinion.

That is how people make a journey at astonishing speed from unfocused alienation to murderous militancy; from vague mistrust of Westminster to deranged conspiracy theory. Politicians are as susceptible as everyone else, whipping each other into factional rages in their WhatsApp groups.

In normal times, that process is slowed by friction from everyday brushes with analogue reality. We might not have seen fleeting conversations at football matches or on the bus as part of our social life, but each interaction with a stranger exercised muscles of empathy and diplomacy that are atrophying.

We are now zooming deep into culturally reinforced comfort zones. It doesn’t have to be that way. The antidote to polarisation is solidarity and there is heaps of that around. The weekly ritual of doorstep applause for the NHS is rightly cherished as an expression of communal spirit to transcend isolation. Images of those moments will be displayed as icons of national togetherness for generations, like the photos of Londoners seeking shelter from the blitz in tube stations, except there won’t be so many people jammed together in the frame.

That is no minor difference. We know there is a vast reserve of solidarity available and that it could be a healing social balm after years of painful division. But it is also a perishable commodity that degrades if left up on the shelf of abstract rhetoric. It needs to be applied in person and it is hard to bring people together without physically bringing people together.

Economic redistribution is the traditional way to put solidarity into political practice, and there might be more public appetite for that than there has been for decades. But it isn’t guaranteed, nor is financial inequality the only gap that will need bridging. The politics of quarantine have focused on the sacrifices involved, on the requirement for discipline and the challenge of repressing our socialising urges. The presumption has been that the springs will uncoil as soon as the pressure is released, and the old ways will bounce back.

But not if the virus has corroded the mechanism. Some habits of trust might have to be relearned. It might require effort on a political and individual level to practice social un-distancing – to reach out of our digital boltholes. Repairing the damage done by this disease will be a project of cultural reconnection, not just economic redistribution. We will need new ways to feel joined for as long as we cannot take each other by the hand.

• Rafael Behr is a Guardian columnist