It was never a secret in my house that I was conceived with the help of an anonymous sperm donor. For a majority of my childhood, I never really thought about him. But when I was around 11, I went through a period of having questions. My parents — I have two mothers — gave me a photo copy of a questionnaire that was sent to them from the sperm bank they used, California Cryobank. The donor filled it out in 1996, two years before I was born.

I remember carrying the form with me in my backpack, taking it to school and studying it occasionally when I remembered I had it. There was this sense of touch — this person had used his hand to answer these questions; I could see where he had crossed things out. It wasn’t that I was so desperate to imagine who he was; it was enough to have proof that he was real, entangled with who I am and yet, as that document showed, totally separate. The form made him concrete, if inscrutable. It also gave me the sense that there was this larger world, this process and this bureaucracy that my existence was built upon. It was a way to help me understand myself.

I knew a lot of other children whose parents had used donors to conceive because every summer we went to a camp for same-sex families. Last summer, news traveled through the community that two kids from two families who attended the camp for years had independently gone on to a registry for family members trying to connect with donors or donor siblings. The two discovered that they shared a donor — that they were half siblings.

Until that moment, it had not really occurred to me — or my mothers, even though one is an ObGyn — that I might have half siblings out there. It makes no sense that we didn’t think about that, because my parents deliberately chose a donor whose sperm had successfully produced at least one live birth, whose sperm had, in a sense, “worked.” I think they were just so focused on thinking about the new family they were creating that they never stopped to think about the implications of the huge, inadvertent social experiment they were joining.

The news about the two kids at camp made me curious to find out if I had half siblings that I did not know about. So that same month, last August, when I was 19, I dug up the questionnaire, went to the sibling registry for California Cryobank, the largest sperm bank in the nation, and typed in the donor’s number. I landed on a message board for children of my particular donor and saw about a dozen cryptic user names of various mothers or children who were perhaps hesitant to reveal themselves completely. One jumped out at me — it said jplamb.

[Sperm donors can’t stay secret anymore. Here’s what that means.]

I grew up in Oakland, but I spent a semester in high school at a program in New York for kids interested in experiential learning, and one friend I made there, I knew, had two mothers who used a sperm donor to conceive him. His name was Gus Lamb. Right away, I texted him to ask if he had registered on the California Cryobank. He said he had. We exchanged donor numbers, and then we knew: We were half siblings.

It was a moment of glee but also of horror. I knew that as a story it was mind-blowing, but it was also disturbing — to have the script switched, to go from friends to brothers. In our experiential-learning program, we were constantly being asked to write personal essays to try to understand our lives. For four months, we were doing that and reading each other’s work and sleeping on the same floor of a dorm, all the while not knowing that we were half brothers — the perversity of that was not lost on either of us.

Sheepishly, we both wondered how that was possible: How could we not have somehow known? But at the same time, we both recognized that it didn’t seem so obvious. I had this suspicious feeling that scientists were conducting an experiment, had taken a lunch break and then forgotten to check back. But no one was watching through the two-way mirror, and instead we were stuck looking at each other, reflected and refracted, different people, but the same, mouths agape. If it was an experiment, the variables had not yielded some thrilling result. There had been no instant connection or unbreakable bond, and we easily lost touch when the program ended.

We got on the phone, me in California, Gus in Massachusetts. Gus told me that he had never been especially drawn to learning more about the donor siblings. His sister Izzy, however, who had the same donor, had done research for medical reasons after having her appendix out. “There’s tons of siblings,” Gus told me. That was another shock. Many of them, he said, had been in touch for years. Gus and Izzy even had video-chatted with a few.

When we hung up, I told my parents what I’d learned, and they were equally stunned. I felt both curious and anxious about these people and what they exactly meant to me. The sheer quantity of them gave me a feeling of having been mass-produced.

Even as I was trying to take this information in, I was realizing that one way I could maybe make sense of all of this was through photography, a medium I’ve been interested in from a young age. I could use the camera as an excuse to meet each sibling and maybe the process of making pictures would help me find some sort of stability, even as I also recognized that conflict, discomfort and maybe even a kind of love would be part of the experience.

The first people I planned to shoot were Gus and Izzy. My younger sister, Ruby, who was conceived using a different donor, traveled with me to their home outside Boston. Hanging out with Gus felt familiar and alien at the same time. Our time at that school together was a prologue; now we were beginning again, and this time I was learning about him in a different way. There are some things about a person you can’t understand without seeing the place where they grew up. It’s a type of access and point of view that allows you to see someone in a very vulnerable state: This was their given life, messiness and all, not necessarily the life they want to build for themselves.

I knew I wanted to try to photograph all the siblings in the environments in which they were raised, and I knew I wanted the images to convey a sense of drama even when depicting quotidian scenes. I decided to learn how to use a view camera, which is a large-format, old-fashioned-looking film camera with bellows. It requires a lot of technical fiddling, focusing and refocusing and finding the right angle, which makes taking pictures incredibly, if not painfully, slow — usually at least an hour. For the siblings, I think taking that kind of photograph was strange, but it also allowed them to sit still and concentrate on the picture as much as I was. The camera makes images that are rich and detailed. I wanted something that was going to feel like the opposite of mass production, that would have none of the slickness that I was starting to associate with the sperm bank. It has a clean, simple, commercial message about helping families and ads that present donors as superheroes, their future babies as geniuses. I wanted to produce something that would be exhaustive and overwhelming, that would complicate the industry’s message — that would refute any simple narratives.

In the picture of Gus and Izzy, they are posed in red plastic lawn chairs that look like blown-up versions of toddler’s chairs. I was after this combination of both a formality — in their almost regal posture — and a whimsy or childishness, as if the chairs had grown up with them.

Gus included me in a group chat that about half the siblings use. From there one led me to another and another until I was in contact with all of them. I kept those exchanges brief, because I wanted to feel the potency of our first encounter.

I took Gus and Izzy to the next shoot. It was the first time I met a sibling that I hadn’t already known, and I was suddenly more nervous than I expected. When we all got out of the car, my hand began to tremble so much that I dropped my keys. The physiological betrayal rattled me, because I knew I was going to have to do this about 30 more times. As a way of managing my nerves in the early meetings with siblings, I was immediately focused on the work, on figuring out where we would take the picture and what kind of image would be powerful. We would walk together through various rooms in the house, contemplate our options, before finally deciding on the right place.

When I met Sadie, a college student in Portland, Ore., she was living in a single room in a small guesthouse, so there was just one place we could take the picture. We spent most of our time talking and listening to “Best of Motown” from a massive speaker she found on Craigslist. She started hunting through things she had bought in thrift stores that we could use in the picture, like the half-moon visible above her head in the photograph. But she also showed me things about her life that we knew were not going to be in the image: her own photos, an album she made of other people’s abandoned shopping lists.

By then, it had become clear to me that 90 percent of the time that I spent with each sibling needed to be unrelated to the photograph itself. It needed to be about our getting to know each other, about my trying to understand the other person’s life. It couldn’t be rushed. The emotional labor of the project was intended to be almost reparative — a response to the transactional nature of the sperm bank and the financial exchange our parents made in order to create us.

So many of these kinds of half sibling relationships that I’ve heard about are hard to sustain because they’re built over text and social media — the geographical separations become too great, which can make it easier for people to distance themselves. You can’t really get to know someone online, this space where we make our lives more consumable for one another. By meeting in person, there was no hiding.

Over 10 months, I traveled to 16 states to meet and shoot the 32 siblings. (One did not participate.) Sometimes I spent an afternoon, sometimes a few days. I decided not to bring an assistant to help with the light or make the process run more smoothly — even if that would have helped produce the best images possible, technically.

Looking through the camera, I had a feeling I couldn’t shake: that these people were all versions of me, just formed in different parts of the country — but were also strangers who might as well have been picked out of a hat. The camera gave me an excuse to study each person — to look deeply at them in a way that without a camera would have been uncomfortable and socially unacceptable.

Every once in a while, I would see something eerie about myself in one of the other siblings that could completely scramble my sense of self — the way that one’s neck became splotchy when she was uncomfortable or the way another one bit his lip. Once, I heard a sibling laugh, and it was so much my own laugh that it made the hair on my neck stand up.

In December, I made a trip to Honolulu, where I visited Kelsi Ikeda at the home in which she grew up. It was the first place I traveled by plane, and I remember waking up in her house that first morning feeling disoriented. It was hot, I could feel the breeze of a fan, it smelled different, and I was in a bunk bed. It took me a while to realize where I was. And I remember thinking: Why am I here? Whom can I hold accountable for this feeling? The bank? My parents? The donor? Myself? What am I doing exactly? And what am I trying to accomplish?

At times, committing to a project like this has felt masochistic. I’m generally an introverted person, and it was hard to feel as if I constantly had to be on, performing the most appealing version of myself. Though the feeling of performance quickly dissolved, I still had a recurring sensation of being in a confused state of just-waking-up, of trying to find my place in all these different parts of America as well as in this strange social landscape.

I spent four days with Kelsi and her family, enough time that by the end I felt a real affection for them all. In her picture, she’s wearing her prom dress from junior year of high school. It feels funny, even tinged with a hint of embarrassment, to try on the clothes of our past selves. But it helped us get acquainted.

During the time I spent with my half siblings, we exchanged secrets. People get very confessional around a stranger who has no stake in their life on a day-to-day basis. We had a connection, which meant they could trust me, but I wasn’t a potential future friend they needed to impress. I was something else — some third thing.

The following month, I met Daniel Claypoole, who could be described as the great connector: He seeks siblings out and sort of holds the group together. He’s social and extroverted and rallies people around the idea of this being a group.

He lives in Savannah, Ga., where he had been going to art school, but I met him in Albuquerque. His two younger brothers, Zeke, 14, and Grayson, 4, who both share our donor, live there. His sister, who is 9, and who does not share our donor, was there, too, and she was trying to explain to Grayson who I was. I don’t know if he understood.

I knew I wanted to make Grayson’s picture on that beanbag chair in their living room. You can’t see it in the image, but the entire wall is covered in a pattern of crosses. I set up one continuous light and instructed Grayson, a typical frenetic little kid, to stay still. Amazingly, he did. Many people find the hot light uncomfortable, but he seemed warmed by it. When we left, he cried, and I felt a pang of guilt. I’m sure he was crying over Daniel, but I also wondered what he made of the word “brother,” which was thrown around when we were introduced, because I knew I would most likely not see him again for a very long time, if ever.

Daniel and I drove to Clovis, N.M., to visit the house he grew up in with his grandmother, grandfather and great-grandmother. I wanted to incorporate biographical details in the photograph, like the painting hanging on the wall of his great-great-grandfather, a man with piercing eyes who, he had been told, was the chief firefighter in Clovis. On the bottom left of the photo you can see a dictionary in which his great-grandmother stores the family photos — the wedding and baby pictures are loosely tucked into random pages.

Even though Daniel has been in touch with other siblings for many years, I was the first sibling from outside the family that his grandparents had ever met. We felt very close by the end of the visit. I felt so grateful for the way that his grandparents welcomed me, just as so many other families had, giving me a place to sleep, a seat at family dinner. It’s strange to think that I have been in all of their homes, but none of them have ever been in mine or met my parents.

I’m always hesitant to call anybody a brother or sister. But many of the other siblings use that language very loosely. I don’t, probably because I already have a sister, and she will always be most important to me.

But I have been struck by the closeness that comes from the intensity of the time that we spent together or, who knows, maybe something more than that. I spent about 12 hours with one of the siblings, Neylan Griffy. She drove me from Denver almost all the way to Kansas to show me where she is from. It was pitch dark, and we talked the whole time. When I was leaving Colorado, and we were saying goodbye, she said, almost with trepidation: “I don’t know if it’s too early to say this, but I heart you.”

She didn’t want to push me or expect anything; she was just expressing her feelings. She was one of the first siblings to connect with others, so she may be more comfortable with that. I laughed and said, “I heart you, too.”

One of the last siblings I photographed was Dawson Johnson. One of the others found him on 23andMe in January and connected me with him. He’d never communicated with a sibling before me. I took Gus on my trip to visit him, and the three of us met at an IHOP. He pulled up in a massive black truck with oversize wheels. He’s muscular, a taekwondo instructor who was a serious high school wrestler. I wanted to portray that side of him in the picture but also to capture something about his manner, which was gentle. In the photograph we made, I placed him shirtless and beneath the truck, in this vulnerable state.

At some point, in each sibling encounter, we would inevitably end up talking about the donor. He represented this absence we all had in common, almost a spectral figure hovering above our lives. Some siblings, once they turned 18, had written to the donor and received long letters back. A different sibling told me that although he wasn’t interested in actually contacting the donor, he wished he had the ability to be invisible, to watch over him for one day as he went about his life, a sort of inversion of the dynamic.

At one point, Izzy got her hands on an audio interview of the donor that the bank made and that another sibling’s mother had. (You can get more information about the donor from the bank — more extensive questionnaire forms or an audio recording — if you pay extra for it.) She, Gus, Kyle Luzzi-Dundon (another sibling) and I listened to the recording one night, huddled in a circle in a sort of séance.

The bank asks the donor at the end of the audio interview whether he has anything he would like to tell any children conceived with his sperm. Our donor’s response: “I wish them all the luck.” One sibling scribbled that on his bedroom wall during high school in colorful chalk as if it were an inspirational quote. I heard it more as an irreverent provocation: My job here is done. May the odds be ever in your favor.

Trying to understand what the donor means to me has been complicated. I never planned on trying to contact him, but I ultimately did to let him know about this project. He declined to be a part of it at this stage. To me, it is more interesting for him to remain the missing and invisible figure he has always been. I don’t think he had any idea, at the time he donated his sperm, that he was creating a kind of time capsule that could potentially explode.

For me, there is a strange pleasure in being able to collapse space and time by putting all these people from all these different locations next to one another. For the viewer, there might be intrigue in searching for the similarities and differences among each of us or even just knowing that we are all connected on this deeper, genetic level.

These pictures also capture a transitional stage in most of our lives — we are at the close of adolescence, on the brink of becoming our adult selves. The basketball hoop has fallen in the front yard; the prom dress has been tucked away in the back of the closet; the bicycle with training wheels will soon be thrown out or given away.

The project has no determined end, because other siblings may emerge in the next weeks, months and years. Once, two siblings who hadn’t met yet but who’d seen photos of each other discovered that they were in an airport at the same time. This incident seemed to confirm our paranoia that we might be walking by siblings all the time without knowing it: in the streets, on the subway, at our liberal-arts colleges.

Since finishing the project, or at least this phase of it, I sometimes feel this haze state fall over me, in which other people start to look like me. One day recently, on the subway, a young man about my age sat down across from me. Medium build, dark auburn hair, full lips, one of the most consistent features in all the siblings. I looked at his hands — they were knuckly and slender. They looked so much like mine. I continued to stare and found myself on the brink of asking him an uncomfortable question. But I didn’t, and instead I thought about what it means to be able to see yourself in strangers — if, in the course of this project, my capacity for empathy has grown, has opened me up, or if the whole thing has been secretly rooted in self-interest, a fixation with understanding who I am.

The photographs have been developed, selected, printed; I stare at them now, see them side by side, I think about the work that made them — and still I’m not sure.

[Sperm donors can’t stay secret anymore. Here’s what that means.]