The poet and philosopher Mark Nepo says that however divided we seem right now, we’re far more connected than we think. To be the best we can be, we have to meet the outer world with our inner world

If you’re worried about the future of humanity, then take heart from Mark Nepo’s reflections on an aspen grove. Aspen trees are lanky, and their bark stretches like ribbons into the sky. As we wander through the grove, says Nepo, we will see individual, separate, tall trees. But what we won’t know as we look at them is that, below ground, they are all connected: linked by the same extensive, interdependent root system. And here’s the point: what happens to one aspen tree affects them all. They might look strong, separate and independent, but they’re totally reliant on one another and on a common, if hidden, survival system.

So here’s the good news from Nepo, a poet and philosopher. In an age that sometimes seems dominated by human difference, and at a time when we’re increasingly aware of the pulling up of drawbridges, what’s visible isn’t the whole story. “On the surface we seem different, and of course each individual human being is unique; but underneath we share the same root system.” The crucial bit, says Nepo, is that evolution has fashioned us to ensure that when the chips are down, when humankind seems to be falling apart, co-operation will prevail. However divided we seem, we’ll come together in the nick of time to pull off a concerted effort that will ensure our survival.

Nepo has written 20 books – Oprah Winfrey included his Book of Awakening in a list of her favourite ever things – and alongside writing others he’s spent the past 14 years researching his latest, out next week, More Together Than Alone. What he could never have imagined when he started out on his quest to understand what makes human beings co-operate and work for the common good is that by the time of its publication it would feel so relevant: the past few years have been marked by a crumbling of the organisations and structures that seemed to unite us, and a sometimes desperate, and certainly desperately worrying, race towards individualism, greed and selfishness.

For Nepo, though, there is optimism. “I’ve always believed in the amazing resilience of the human spirit. I feel there’s a lineage of care and working well together – but the noise of things falling apart is much louder than the noise of things coming together. And in truth, both those are happening at the moment. Right now it feels like we’re in an age of cruelty – and it’s not clear where it’s all going yet. But what I want to say is, the things we care about matter more than ever. If we truly are on the edge of another Dark Age, it’s incumbent on all of us to keep the literacy of the heart alive.”

That, says Nepo, is what’s happened throughout history: when humankind looked like it was tearing itself apart, the actions of groups of seemingly altruistic individuals kept the flame of concord and synergy together. He tells the story of Holocaust survivor Elie Wiesel, who described an event he witnessed on a Nazi march. The prisoners were being forced to run barefoot through the ice and snow of eastern Europe, and those who slowed or stopped were trampled to death. In the midst of this, a man stumbled, and to save him the others close by threw themselves on top of him. The Nazis couldn’t shoot them all: in the end, the soldiers beat the marchers till they all got up, and walked on.

The story, says Nepo in his book, is “a painful koan that holds the essence of community. As kind and brave as it is brutal, this moment is a testament to the lengths we’ll go to to care for each other, if led or pushed to our true nature.”

The actions, as I say, seem altruistic: but Nepo’s point is that this is more than altruism, because in saving others we save ourselves – it’s back to the aspen grove again. “If the common root gets diseased, then in the end that’s bad for all of us,” he says. And what makes us aware of our interdependence is our interior workings. “It’s not just navel-gazing: how we understand ourselves is how we contribute to the work of the whole,” he says.

His book is steeped in examples of historic interdependence and community. There’s the Gandhara Empire, in what is now Pakistan, whose extensive Taxila university provided the finest free education. The Chan school of Buddhism is another, whose students formed a network that established a spiritual lineage that existed for hundreds of years and gave the world the gift of zen. And there’s the story of the integrated culture that united Muslims, Jews and Christians in southern Spain between the years 750 and 1492: “a 742-year moment of community”, as Nepo calls it.

And then there’s the awesome story of the bell of Nagasaki: in the aftermath of the dropping of the atomic bomb in 1945, one column of the Japanese city’s cathedral somehow survived, and in the desperate days that followed, someone managed to crawl to it to ring its bell. Its peal served as a signal to begin again, and it continued to be rung in the days and months that followed; a symbol of the continuity of community, and the existence – even in the midst of such unthinkable devastation – of hope.

On an individual level, Nepo believes, we are especially open to the connectedness of life on two occasions: times of great love and times of great suffering. For him, the epiphany came when, 30-plus years ago, then in his 30s, he was diagnosed with cancer and almost died. “All of a sudden I was thrust into this ward with lots of other people in the same situation. And what I discovered was the quiet courage and wisdom that connected us all. No one would choose suffering, but what erosion is for nature, suffering is for humans. I believe life has been made just hard enough that we need one another; and through experiences of great suffering and great love, we are reduced to what’s essential.”

For him the turning point was his cancer, for others it might be falling in love, or having a child. The crucial feeling, he believes, is vulnerability: becoming vulnerable, and embracing the potential of feeling vulnerable, is the starting point to understanding ourselves.

Not feeding an inner life, says Nepo, “feeds the toxic side of humanity”. To be the best human beings we can be, we have to pay attention to our interior life; if we don’t, exterior forces may feel as though they’re crushing us. “We have to meet the outer world with our inner world,” he says.

The bottom line about the way human beings react to one another, according to Nepo, is summed up in what he says happened “in the very beginning”, when one early human being chanced on another. One of them, the more fearful one, responded by rejecting the other – “You’re different! Go away!” But the other, who was more curious, had the healthier response that carries humankind forward: “You’re different! What do you know that I don’t know? What can you teach me?”

And as with the archetype, so with the individual: because inside each of us, he believes, are both these instincts. We’ve all had moments when we’ve wanted to reject or repel another human being; and we all know it’s more generous, more open and all-round better to be welcoming, to be interested, and to be humble.

The story of human history, says Nepo, is this journey writ large: a pendulum-like voyage through times of great co-operation and other periods of terrible mistrust, even genocide. “Throughout history you have swells and crests where we move towards each other, and then away. It’s unclear exactly what’s happening right now but in the US for sure [he lives in Michigan] what we’re seeing is a retreat to a fear-based way of reacting to anything different.

“But what I also believe is that there are the beginnings of a recovery – and that happens whenever we recognise another, whenever we reach out, whenever we’re welcoming. One thing we know is that when things that are different start to happen, fear makes us think that what we need is self-interest; but then love and suffering come along and affirm that we really are more together than we are alone.”

More Together Than Alone: The Power of Community by Mark Nepo will be published by Rider Books on 19 July at £12.99. To buy a copy for £11.04 go to guardianbookshop.com