SOME issues permanently smoulder on the horizon, like fissures in the earth. And we don’t know whether those occasional steamclouds are dying gasps, or a reminder of the bubbling lava below.

It sometimes feels like that with the death penalty. I did the usual disheartened double-take when I saw this week’s YouGov poll on attitudes to capital punishment for murder in Scotland.

Yes, at least it’s a minority – 41% for the death sentence, 44% against, with independence supporters slightly (but weirdly) more avid than the average (44% for). And compared to a 2015 Panelbase poll, it’s on the descent from 55%.

Brexit, perhaps unsurprisingly, has expelled some extra puffs of sulphur. Polling data from the British Election Study shows that if you approve of state execution for murder, it predicts your Leave vote by over 70%.

The recent UK Home Secretary Sajid Javid allowed two British Jihadis (the “Beatles” Two) to be extradited to the US. However, it was under terms which – for the first time in 50 years – allowed British subjects to be potentially executed there. A dog-whistle on the death penalty has just been blown.

There has also been a smattering of Brexit Party backwoodsmen waving the noose, hoping to exploit the general dysphoria of the moment.

But there it sits in any case, however it’s politically refracted.

We have a large and enduring minority who believe that murder (as well as some other utter violations, like child rape) should be met with murder.

The Scottish phone-ins have juddered with this sentiment over the last few days, as the teenage killer of Alesha MacPhail had his sentence reduced by three years.

If you have let yourself anywhere near the media on this trial (one read-through was enough for me), it’s evident that the teenager was a special brand of psychopath.

As cool and calculating, as brutally instrumental, sexually disruptive and absent of empathy, as any of criminal history’s horrors.

A human being capable of this has to be definitively removed from the community by our criminal justice system. Yet it’s how that removal is effected – socially, institutionally, or lethally – that still seems to be a live option in the hearts of the public, even in the most apparently liberal and progressive societies.

In last week’s column, faced with violence everywhere in my arts menu, I dipped my cup into the river of scholarship that runs between biology and culture, nature and nurture. With this topic, it seems impossible not to go there again.

A startling recent book, The Goodness Paradox by Harvard anthropologist Richard Wrangham, has an ambition to explain this elemental moral divide around capital punishment.

Our Scottish percentages map to some of our oldest philosophical positions on human nature. Emile Rousseau imagined that we were originally good-hearted creatures, just distorted by the conditions of our upbringing. Judicial killing denies the possibility that our personal evils could be socially determined – and thus diminished, if not reversed.

Thomas Hobbes believed that life, and human nature, were essentially nasty, brutish and short-termist. Only a powerful state – with absolute power over mortal existence – could compel such a human nature to behave in a non-destructive way. Thus, a death sentence would be a necessary sanction.

As Wringham notes, both Rousseau and Hobbes are partly right. We are consciously capable of infinite tenderness and great cruelty, “both a goat and a lion”. How did we become this chimaera, this bizarre animal with two moral bodies?

Wringham, as evolutionary biologists tend to do, compares modern humans to both our simian cousins, and to hunter-gatherer societies, past or just barely existing. Two types of aggression are his focus – reactive (“you touch me, I hit you”), and premeditated (“let’s plan our attack on him”).

Chimps are high on both kinds, but (by comparison) humans’ levels of reactive aggression is much lower, and our premeditated aggression much higher.

In Wringham’s terms, homo sapiens triumphed over our competitors because we “domesticated” ourselves.

That is, we figured out how to cooperate better as groups, using language and culture to mutually depend on each other.

Of course, sapiens uses its social skills to define their groups against other human groups. This generates cultural diversity, property rights – and, of course, wars (which are the ultimate “premeditated aggressions”). There’s a sadly accepted realism about this in the human sciences.

But Wringham cranks this up to a new level. Based on his extensive fieldwork, he suggests that one powerful outcome of our group powers, our language-enhanced capacities to conspire and plot, was that the community could effectively deal with “alpha males” (those whose aggression was reactive, destructive and chaos-making).

And by what means? Effectively, capital punishment. Organised groups of males, claims Wringham, stealthily took out these untameable disrupters. These actions, when conducted over tens of thousands of generations, pushed that trait to the margins of the sapiens gene-pool.

The professor derives this conclusion from the fossil record, but also from his close observation of chimp and bonobo colonies, as well as our remaining hunter-gatherer communities. For the humans, if derision and ostracism didn’t work to contain the chaos-maker, they would impose the ultimate sanction.

Wringham (I just realised: nominative determinism alert) is at extreme pains to say that he’s resolutely opposed to the death penalty in the present. In this, he represents the sophistication of contemporary takes on humanity from a biological perspective.

When these scientists think they’ve identified a deep evolutionary driver, they see it as part of an ever-richer picture of human nature – a picture in which human imagination and creativity can always leap beyond and ahead of our animality.

Yet these deep drivers represent the bass notes in our behavioural orchestra – low, rumbling, insistent.

Let’s say Wringham is right. If so, given how ancient this pattern of responses, it’s no surprise that “flog ‘em, hang ‘em” attitudes persist so strongly in any modern society. One that’s made up of evolved humans, anyway.

Yet he has his critics. They suggest there might be additional behaviours, other than the execution of strangers or disruptors, by which sapiens might have “domesticated” its own extreme aggressions. Caring female networks might also have applied their pressures, steadily resisting mating with these a-social, ill-adapted males.

Also, language and imagination might well make war and enmity – or “coalitionary proactive aggression”, as Wringham terms it – all too possible. But those same faculties can also support an MLK, a Gandhi or a Greta Thunberg.

That is, those who can strengthen the viability of a human community by proposing new, inspiring but non-violent practices.

Older readers may remember one instance in Scottish criminal justice where “new, inspiring but non-violent practices” were applied to the seemingly least improvable of criminals: the Special Unit at Barlinnie Prison. Running from 1973 to 1984, the Unit deployed arts, facilitation, psychotherapy and comfortable conditions to defuse many human bombs that passed through, including the artists Jimmy Boyle and Hugh Collins.

The Scottish criminologist David Wilson – presenter of Crime Files on BBC Scotland – suggested this week that the killer of Alesha Macphail “will be released at some date, and I’d rather he came out after being treated … if they brought back the Barlinnie special unit they could treat him”.

History tells us that Barlinnie was the scene of some of the last few capital punishments conducted in Scotland – the serial killer Peter Manuel in 1958, and the teenage murderer Anthony Miller in 1960. So, on the scales of the human condition at least, it balances out between Hobbesians and Rousseauvians; both the lion and the goat.

Barlinnie might become the most interesting place, once again, to wrestle with the two-headed chimaeras of human nature.