Taryn Simon: A Living Man Declared Dead and Other Chapters, Tate Modern, London

A young star's perturbing show highlights the tenuous nature of individuality

Taryn Simon is only 36 but already she's a star of the New York art world, collected by MoMA, represented by Damien Hirst's dealer, Larry Gagosian, and laden with awards and superlatives.

Steven Spielberg has attended her openings, although that may be partly because she's married to Gwyneth Paltrow's younger brother. And her latest perturbing work – photography that holds an argument with itself about the relative merits of fine art and photojournalism – gets a stand-alone show at Tate Modern, an accolade that is arguably the UK equivalent of the blessing of the director of Jaws.

There is something keenly perverse about these serried rows of smallish photographic portraits, carefully arranged as 18 horizontal family trees. Even absences are recorded, with a square left blank and a note with the reason for that person's non-appearance: "jailed", or "flu", or simply "location unknown". These empty spaces tell us more about Simon than the portraits do about her subjects. She is a photographer who wants to order chaos and photograph absence.

Socially, and geographically, the show's scope is wide. Simon has gone to inordinate lengths to obtain accurate information about clan war in Brazil, polygamy in Kenya, or thalidomide victims in Scotland. Her lines of relatives have both the sinister regimentation of the eugenicist and the forward thrust of the optimist: the youngest subjects are a generation away from the massacre of Serb Muslims at Srebrenica in 1995. One day, we may reach the best of all possible worlds, although the bleak faces of Ukrainian orphans facing summary ejection from their cash-strapped institution on turning 16, and many with a future in crime or sexual exploitation to look forward to, suggest that day won't come soon.

The sets of images all follow the same format. The show's title comes from Uttar Pradesh, where land is both vital and scarce, and officials are bribed to declare people dead so their relatives can dispossess them. Photography, says Simon, is the greatest proof of life – an odd statement, since who, apart from these Indian victims of profound injustice, needs to prove that they're alive?

"I was looking for patterns and codes in the stories," explains the artist, who has travelled the world seeking out families whose lives are less orderly than most. The only indication of where she's been is the written description of each group of figures and the panel housing ancillary material. Otherwise, we have simply a bunch of people who resemble each other, more or less, and whose identical poses reinforce that resemblance. This sameness dulls the eye: the portraits evaporate from the memory, like ghosts, or dead people, or living people who have been declared dead. Their homogeneity is both boring and frightening, which is part of the point.

Individuality is tenuous. Hans Frank, who ran Poland for Hitler, or the Bosnian Serbs who committed the biggest massacre since the Second World War at Srebrenica, certainly didn't differentiate between victims. Actually, these last victims are some of the portraits that stick most in the mind, because they are not of whole people but of molars, dug up and DNA-tested to confirm their origins.

Simon, whose projects have included shots of contraband at JFK airport and portraits of people wrongly convicted of violent crime, is interested in the untoward – in human debris. Ultimately, this peculiar, unlovely but intriguing exhibition is no less than an attempt to photograph fate. You can take issue with Simon's methods, but there's no faulting her ambition.

To 6 Nov (020 7887 8888)