The premise of A Possible Life is existential rather than narrative. The most successful genetic mutation of all time has permitted the self-awareness that allows human beings to "empathise, guess, manipulate, out-think, out-fight  and, where necessary, co-operate". The physical site of this mutation is discovered in the third of the novel's connected stories, "Everything Can Be Explained", by a pair of young women scientists who discover that loop within the brain where the sense of selfhood is "retuned, refined and enriched" by memory. This story is set in the near future; other sections of the novel look back to the second world war, to a boy struggling for survival in a Victorian workhouse, to a French peasant girl's deception in the early 19th century, and to the 1970s, where a brilliant young woman singer/songwriter makes her first recordings.

The irony with which Faulks places co-operation last in the list of actions brought about by human self-awareness reflects a fictional world where war and the battle for survival dominate. In the first section, "A Different Man", Faulks returns to material he explored in Charlotte Gray, seasoning it with a dash of black humour reminiscent of Waugh's Sword of Honour trilogy. Geoffrey Talbot is a fine cricketer, an homme moyen sensuel who is bilingual by accident of upbringing, and becomes a British agent in occupied France. The territory is lightly but deftly covered, and the rather opaque character of Geoffrey is finely judged.

However, when Geoffrey is taken prisoner, held in a concentration camp and forced to participate in Special Unit operations which include shovelling dead or not-quite-dead children into crematorium furnaces, Faulks goes beyond his capacity. In Charlotte Grey, his judgment was true: the little French children, André and Jacob, are fully known in their journey from family security to extermination. The novel takes them to the black mouth of Auschwitz, to disappear over its threshold with a finality that is the more memorable because Faulks understands exactly how far he can accompany these children.

Every story within this novel bears the imprint of an extremely accomplished writer. In a sense Faulks is profligate with his own talent, and sometimes seems to put too little value on what this talent can do with idiosyncratic ease, and too much on what does not lie within its range. The workhouse child Billy in "The Second Sister" has a voice so compelling, self-deceiving and deeply human that most novelists would have been happy to build a whole novel around him. Faulks, however, wants something different. Billy must step back into the shadows, while the novel uses him for illustrative and thematic purposes.

Faulks is fascinated by communal memory, and the ways in which the dissolving grains of an individual life may carry its purposes into other lives. The midden and chained dog past which Geoffrey Talbot wheels his bicycle into the French farmhouse where he will be betrayed to the Gestapo are the same midden, dog and farmhouse that betrayed the peasant girl Jeanne over 100 years earlier. The record producer and musician who tells the story of his love for the Joan Baez-like Anya King will later consider buying a flat in a former Victorian workhouse. Although it is now "full of saunas and fitness rooms", Billy Webb once picked oakum there, and slept in a hole in the floor.

The cells of the past, recyled, reused, never quite destroyed, are real rather than haunting presences throughout A Possible Life. If matter does not disappear, then the matter that made Billy Webb is always present somewhere, exerting its influence. The cessation of an event does not bring about its ending, if it continues to throb and relive itself through memory. The whole novel is an indictment of the cod psychology that advises human beings to "move on", shucking off their pasts as if these were a skin rather than an impregnation of the entire being. And what is true of the individual may also be true of a culture and nation, which cannot reinvent themselves without taking account of the fabric from which they are made.

Not to remember, of course, is to risk the demon of repetition. Many of the repetitions within A Possible Life are grim, but there are rare, benign presences that light up the path from one generation of betrayal to the next. In one fine scene, Geoffrey Talbot, no longer able to function under the burden of memory, is visited by a former pupil whom he once coached in cricket. The visit is everyday, even banal, but richly humane. The young man, Ched, realises that Geoffrey would like to be able to watch test cricket, and a week later, a small portable TV with a built-in aerial and earphones arrives at the asylum. Ched's detailed thoughtfulness, without attachment or expectation, is the beginning of Geoffrey's recovery. In A Possible Life, such moments of grace are the only relief from the treadmill of time.

 Helen Dunmore's The Greatcoat is published by Hammer.

What makes a life? What determines how and why we become the people we do, over a lifetime? What electrical impulses or conjunction of atoms create "this miracle of thought in flesh"? And what does it mean to have lived?

These questions have underpinned Sebastian Faulks's fiction since the beginning. But it was his seventh novel, Human Traces, that explored most explicitly this relationship between thought and flesh and the historical mapping of it through the stories of two 19th-century doctors. These same concerns are watermarked through A Possible Life, a novel that takes the form of five biographical portraits, each a self-contained novella but carrying echoes of the lives that go before and after, like the movements of a symphony. Sometimes these connections consist of a physical object  a statue or a building  linking two characters a century apart. More often they are less tangible; ripples sent out through history by one small act of kindness, one chance meeting.

The book begins in familiar Faulks territory, with the narrative of Geoffrey Talbot, a young prep school teacher who, in 1939, finds himself volunteering for undercover operations in occupied France. The following narratives shuttle back and forth across the 19th and 20th centuries and into our own, sharp with historical detail. After Geoffrey comes Billy, a workhouse boy whose grit lifts his children out of Victorian poverty into the prospect of a different kind of life.

The central story belongs to Elena Duranti, and is the only one that projects forward from the present into an imagined near future. A solitary child who grows up in a rural Italy decimated by economic crisis, Elena becomes a neuroscientist celebrated for discovering the elusive locus of self-awareness in the brain; proof, in other words, that there is no such thing as the "soul". Her discovery is fictional but based closely on real case studies; Faulks is concerned with what such a discovery might mean for our collective sense of our humanity. "Knowing one was comprised of recycled matter only and that selfhood was a delusion did not take away the aching of the heart."

Each of the lives unfolded here, in their distinctive voices, yearns towards the comprehension of this paradox. To varying degrees they seek connection with others, whether through sex, words, music or silence. Though their stories are necessarily compressed, Faulks makes his characters real with spare, careful details. From the unspeakable horrors Geoffrey witnesses in his German prison camp to the striving after perfect self-expression of the young folk singer Anya King in the book's final story, the writing is masterfully controlled, without a word wasted. Avoiding excess emotion, Faulks evokes a deep compassion for all his troubled characters and, by extension, for all of us who share their condition. As Jack, the narrator of the final section, says: "The events and the sensations, the stories and the things that make me what I am in the eyes of other people, the list of facts that make my life They could be mine, they might be yours."

A Possible Life is a profound novel; if it lacks the obvious narrative drive of works such as Charlotte Gray or Birdsong, it compensates by exploring big ideas without compromising the human drama. It is also, ultimately, an optimistic work. We may be no more than matter but we can, in various ways, outlive our short lifespan, perhaps never knowing how far our ripples will reach.