“It’s all right; I’m a Unitarian,” says Elizabeth Marshall Thomas as we settle into chairs in front of the altar of the Unitarian Universalist First Parish Church in Cambridge, Mass., to talk. The adjacent meeting rooms are packed with visitors to the New England Independent Booksellers Association’s All About the Books event, at which she has just read an excerpt from her new title, A Million Years with You: A Memoir of Life Observed (Houghton Mifflin Harcourt, June). The church proper is the only quiet spot available for conversation and this iconoclastic author sees nothing amiss in appropriating a place of worship for another purpose. Now 81, Thomas has been disregarding conventional boundaries ever since an elementary school librarian told her she couldn’t read any more books about animals because “there were more important subjects.” The young Elizabeth promptly went home and wrote her own book about a tiger.

It would be another half-century before Thomas would publish her first professional work on animals, the bestselling The Hidden Life of Dogs, in 1993. But she continued to follow her independent instincts during the intervening decades. In 1951, she took a break from Smith College to live among the Bushmen in Africa’s Kalahari Basin. The book that resulted from her Kalahari expeditions, The Harmless People (1959), prompted New Yorker editor William Shawn to commission an article about the Dodoth people of northern Uganda. By then she was a mother, so she took along two-year-old John and four-year-old Stephanie on travels that included a brush with a belligerent army officer named Idi Amin.

Husband Steve joined them for the next New Yorker assignment in Nigeria, where they were trapped when a civil war closed the borders. “The Nigerian experience was so bad I didn’t want to write about it,” says Thomas. A Million Years with You contains an account of that difficult period. She saw dead bodies in the streets. She was unable to get medical care when Stephanie had a dangerously high fever, and she spent a terrifying 48 hours waiting for Steve and John to return from a drive through an area where she learned people were being dragged from their cars and killed. “I felt bad about not delivering a manuscript to the New Yorker,” she continues. “They published the whole book about Uganda [1965’s Warrior Herdsmen] in several issues, and Mr. Shawn was a wonderful editor. His editing sounded just like my own writing, but it was so much better—I read it and thought, ‘I had no idea I was that good!’ But I just didn’t want to write anymore.”

Thomas says candidly, “I started drinking heavily—that took some time.” (Now a member of AA, she describes her struggles with alcohol in the memoir.) “Then came my daughter’s accident.” Stephanie was run over by a tractor and paralyzed at age 17; after hospitalization, she was sent to a rehabilitation facility in Boston. To be near her, Thomas moved from their home outside of Washington, D.C., where Steve worked for an arms-control organization. When Stephanie completed rehab and entered Radcliffe, her mother “got three teaching jobs all at the same time, to keep myself too busy to think about my problems.” A book about the family’s many dogs had been on her mind. Then, unexpectedly, a different kind of writing elbowed its way onto her agenda: fiction about hunter-gatherers living in Siberia during the Upper Paleolithic.

“I had told the story of Reindeer Moon to my kids when they were little, and they loved it,” she recalls. “Years later I was talking to a very good friend of mine about it, and she said, ‘If you don’t write it, it will never be written.’ That was true, and I knew it, so I quit my job, moved to New Hampshire, and started writing.” Steve, who had become a consultant, soon joined her there; they live on the farm Thomas’s father bought in 1936.

The success of Reindeer Moon (1987) and its sequel, The Animal Wife (1990), gave Thomas the confidence to embark on the kind of animal studies she’d wanted to do since childhood, but had reluctantly set aside because they weren’t intellectually respectable. “People didn’t think animals thought, or remembered, or had minds!” she says indignantly. “They most certainly do: any pet owner knows more than a lot of scientists about animals.” The Hidden Life of Dogs was the first in a series of books, including The Tribe of Tiger and The Hidden Life of Deer, offering a fresh view of domestic and wild animals based on observation and interpretation that stressed their commonality with humans.

“Why wouldn’t we have commonality?” aks Thomas, speaking of this still-controversial idea. “One of the things I learned from the Kalahari is that we are animals; the Bushmen lived as other savannah animals do, and we as a species come from that Old Way. When I write about animals, I use anthropological techniques and the language you would use for a person. You don’t have to anthropomorphize animals, just acknowledge their individuality. At one time it was forbidden to call an animal anything but ‘it,’ but I always call an animal ‘he’ or ‘she.’ ” When Thomas enthusiastically describes her current research on bacteria, however, she acknowledges with a laugh that you can’t refer to bacteria in gendered terms: “It has to be ‘it’—but it can be ‘who’!”

Small, slim, and tanned, wearing practical country clothes, Thomas has the no-nonsense manner and economical way with words of someone who, as she writes in A Million Years with You, “is not especially reflective.” Was it challenging to write something as personal as a memoir? “I found it extremely instructive,” she replies. “I would write about certain things and find myself thinking, ‘Why did I do this? Why did I feel that way?’ Some things came as a surprise. I never quite realized when my father was alive, for example, what an influence he had on me. We were very close, but I didn’t see until I wrote the book, that the outdoors, wildlife, wild places, animals—it all came from him. I knew my mother was a big influence; she became an anthropologist when she was 50, and she always said life begins at 50.”

Thomas is living proof of her mother’s maxim, having published eight books since she turned 50. She’s finding it more difficult to write now; Steve was diagnosed with ALS about five years ago, and she cares for him at home. “He needs quite a bit of care, and I can’t write in bits and pieces, an hour here or there; I have to settle in and focus. I used to love looking at the calendar and seeing a whole week with nothing written on it.”

Nonetheless, work on the bacteria book progresses, fueled by its thematic links to the belief that has guided Thomas from her early anthropological texts through fiction to her refreshingly empathetic studies of animals. Her interest in bacteria was sparked, she says, by American biologist Lynn Margulis’s groundbreaking writings. “She showed how life on Earth was formed by symbiosis, that we really are just different forms of one single thing. That was very important to me; that’s how it all started.”