Henry Horn, Professor Emeritus of Ecology and Evolutionary Biology and founding director of the Program in Environmental Studies, died in Princeton on March 14 at the age of 77.
Horn joined the faculty in 1966 and founded the Program in Environmental Studies in 1991. He transferred to emeritus status in 2011, although he continued to be active in teaching and research. Just two weeks before his death, Horn submitted a manuscript for his second book on the social behavior of butterflies.
Horn’s breakthrough work was on the geometry of trees, but he was a true naturalist with a deep knowledge of the ecology around him. Professor Emeritus of Geosciences Lincoln Hollister said that Horn transmitted his “keen curiosity of the natural world” to students, colleagues, and the community through walking tours, which he conducted in and around the University campus.
Assistant Professor of Ecology and Evolutionary Biology Cassie Stoddard said Horn was the first person she would tell about a unique bird or tree she came across. She remembers Horn walking briskly down the hallway to tell her about his encounters with hummingbirds in Arizona.
“He was always with binoculars, a notebook, and a pen. He loved observing the natural world and sharing it with others,” Stoddard said. Horn’s broad interests, passion, and curiosity “brought everyone together in the department.”
“He loved to communicate his love of nature to other people,” said James S. McDonnell Professor of Ecology and Evolutionary Biology Simon Levin.
Horn was born in Philadelphia on Nov. 12, 1941. He earned a Bachelor of Arts at Harvard University in 1962 and a Doctor of Philosophy at the University of Washington in 1966, where he completed a doctoral thesis on the social behavior of blackbirds.
Horn’s research was expansive, exploring everything from forest dynamics to insect behavior. His first book on tree shape and branching patterns, “The Adaptive Geometry of Trees,” was published in 1971.
The University’s campus and surrounding areas, including the Institute Woods and Carnegie Lake, served as areas for his fieldwork and teaching. Horn was known for giving weekly walking tours on Friday mornings, sharing his knowledge on the local flora and fauna. Some of these tours were documented by the Office of Sustainability in a “Nature Walks” series, where Horn provided insight on trees, skunk cabbages, black squirrels, and more.
A modern lack of interaction with the natural world concerned Horn. Dan Rubenstein, Class of 1877 Professor in Zoology and Ecology and Evolutionary Biology, said people today are raised to look at nature in a romantic sense, but do not truly understand the patterns and the species that live there.
“He felt that natural history was a lost art,” Rubenstein said of Horn. These nature walks were lessons into “how to read a landscape,” a way to share what he knew of the world with others.
The Friday morning after Horn’s death, Stoddard took a nature walk at Carnegie Lake with members of her lab to honor his legacy. While there, she bumped into another group doing the same.
“We needed to get out and celebrate Henry’s life and his love of natural history by being outside,” Stoddard explained. Seeing another group, Stoddard said, “showed me what a huge impact Henry had on members of this community, on this campus.”
Stoddard, who co-taught a seminar class for first-year Ecology and Evolutionary Biology graduate students with Horn, remembers his devotion to mentoring the next generation of scientists. Horn made students feel comfortable, sharing not only scientific ideas but personal hopes, dreams, and fears.
“He was always striving to learn more, do more, share more, help more,” Stoddard said, “growing, and learning, and interacting,” even though he was an emeritus professor with a long career.
Dylan Morris GS was a student in one of these first-year classes, then co-taught by Horn and Assistant Professor of Ecology and Evolutionary Biology Christie Riehl.
Horn wasn’t afraid to challenge students and was willing to disagree, Morris said. This made Morris, and others, feel respected as scientists.
“He made me feel so welcomed and so valued as a scientist,” Morris said.
At graduate and department seminars, which Horn almost always attended, Rubenstein said Horn was known for being the first to ask questions — questions that made him stronger, more confident, and a better teacher.
One could always count on Horn for a brilliant, insightful question, Stoddard agreed.
David Parris GS ’70, Curator of Natural History at the New Jersey State Museum, recalls Horn grilling him with such thought-provoking questions during his Master of Arts General Examination. Parris, who took a class with Horn during his first semester, remembers Horn as an animated and engaging instructor. Horn told the class about his thesis work with blackbirds, and how he became so familiar with the population that he could identify each bird individually.
“He wasn’t just a brilliant theoretical biologist,” Parris said. “He still knew the ‘woodsy lore,’ as he called it.”
Horn also frequently attended department social events, arriving at Beer Hour with a homemade beer cozy, Morris said.
“He was committed to making this place a family,” Morris said. “He had an incredible commitment to showing up, both socially and academically.”
Horn was a sought-after source of information on environmental preservation for Princeton’s town council and zoning boards. According to Hollister, people looked to him for advice and often quoted him at meetings. Horn was also devoted to education and trained local science teachers during summer programs. There, he focused on a hands-on approach, building a foundation for future learning based on the senses.
“He made a huge mark on many people,” Hollister said, “teaching from what you can feel and see.”
In 2000, when the natural history museum housed in Guyot was planned for removal, Horn and other Ecology and Evolutionary Biology and Geosciences faculty took a stand against it, Hollister said.
Horn felt the collections should be protected and saw the museum as a place for people to interact with the organic world, Parris said.
Parris used to lead tours of the museum on Alumni Day alongside Horn and his wife, Elizabeth.
“He knew the importance of people seeing real objects and real specimens,” Parris added.
In addition to his role as scientist and naturalist, Horn was an author, artist, and musician. He often performed alongside his family and was a member of the Chapel Choir and Musica Alta, and was director of the Madrigal Singers from 1975 to 1989.
Morris, who joined the Chapel Choir at Horn’s encouragement, said that Horn brought his sense of humor to rehearsals.
One piece they performed was about woodland animals blessing the Lord. Horn, poking fun at the lyrics, drew out an ecological analysis of the creatures involved. He concluded that the ecosystem had too many predators, Morris said.
Horn often occupied alter egos to channel his creativity, with invented names like J. Charles Farnesworth and Elizabeth Seaport.
As Farnesworth, Horn made collages out of circuit boards and computer chips, shaping them into natural landscapes. Horn also carved wooden animals, which he displayed in his office and used as teaching tools to get students excited about the “whimsy and magic” of the natural world, Stoddard said.
Horn also consulted for the “Nature’s Nation: American Art and the Environment” exhibition at the University Art Museum and was collaborating with Hollister and others on a 50th anniversary celebration of “Blue Marble,” a photograph of Earth taken on the Apollo 17 mission in 1972.
Horn served on the Princeton University Press Editorial Board from 1993 to 1998 and was chair in 1998. Along with Levin, he co-edited “Monographs in Population Biology,” a series of books examining plant and animal ecology.
Alison Kalett, Princeton University Press Editorial Director of Sciences who worked with Horn and Levin on the Monographs, said that Horn could always be counted on for long, thoughtful responses to the proposals she sent him.
“What I will remember most is the generosity of his feedback and the depth of his thoughts,” Kalett said. “He was very deeply invested in the success of the series and us publishing the best books we could.”
For students, colleagues, and strangers alike, Horn was generous with his time and gracious with his advice and knowledge. Levin said Horn’s door was always open.
“He always placed other people’s interests before his and seemed to revel in being able to help,” Levin said.
Horn’s deep knowledge and generosity as an advisor and mentor made him an anchor for many of the diverse groups he was a part of.
“In a way, he was the tribal elder of all the groups he was in,” Rubenstein said. “He had a sense of history and continuity, so that you always had a slightly different perspective when you talked to him.”
“He was a community backbone for every community he was a part of,” Morris agreed.
Horn’s loss will be felt deeply by members of his department and beyond.
“The department will never quite be the same,” Stoddard said. “Henry was the heart and soul and lifeblood.”
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