Stephen Jay Gould was born in New York City and raised in Bayside in the borough of Queens. On a trip to the Museum of Natural History with his father, five-year-old Stephen was captivated by the giant dinosaur skeletons. The majesty and mystery of these ancient creatures exerted an enduring fascination. Soon, he was reading everything he could find about dinosaurs, fossils and evolution.

As a youngster, Gould also enjoyed playing stickball in the street, and poker at home, a game that stimulated his interest in the laws of probability. He was also a lifelong music lover. As a teenager he was a member of New York’s All-City High School Chorus, and he continued to participate in choral groups for the rest of his life. But his thoughts continually returned to the dinosaurs in the museum. When he learned that there was a field of study called paleontology, and that an adult could have a career seeking the fossils of extinct animals, his course in life was set. With only the slightest knowledge of what this career would be, he moved inexorably toward his goal.

Gould’s parents were the American-born children of Jewish immigrants from Eastern Europe. There was no precedent of higher education in the family, but his parents supported his academic efforts and also encouraged a strong interest in current events and public affairs. As an undergraduate at Antioch University in Ohio, Gould was active in the Civil Rights Movement. When he spent a year abroad, studying at Leeds University in England, he organized weekly protests at a dance hall that refused to admit black customers, until the management relented and integrated the establishment. While still at Antioch, Gould served as a student intern on a seagoing expedition with the Woods Hole Oceanographic Institute. While docked in Bermuda, he collected a number of fossil specimens, land snails preserved over hundreds of thousands of years. Returning to Antioch with his finds, he discovered that a geology professor, A.C Swinnerton, had left the university his own large collection of snail specimens, which he had collected in Bermuda decades earlier. With so many specimens from one location to examine, Gould decided to make them the topic of his senior thesis. He graduated in 1963 with a degree in geology and philosophy.

Gould continued his field work with snails as a graduate student at Columbia University. From Bermuda, his attention shifted to the snails of the Caribbean islands. He became the leading authority on the snail known as cerion. Roughly 600 distinct species of cerion have been identified, and the unusually rich fossil record of their development presents an excellent model for the study of the evolutionary process. On completing his doctorate in paleontology at Columbia, Gould was hired by Harvard University, an association that lasted until his death.

In 1972, Gould and a colleague, Niles Eldredge, published their theory of punctuated equilibrium, a landmark contribution to the study of evolution. Until this time, the prevailing view was that the process of evolution occurs at a continuous, steady pace. From exhaustive review of the fossil record, Gould noted that successful species remain stable for long periods of time, and that the branching of one evolutionary line into a number of different species happens in relatively short periods on the geological timeline. Although punctuated equilibrium was not universally accepted, Gould had stepped into the vanguard of evolutionary theorists.

The following year, he was named Professor of Geology and Invertebrate Paleontology and became curator of Harvard’s renowned Museum of Comparative Zoology. His major scientific publication of the 1970s was the book Ontogeny and Phylogeny (1977), in which he discussed the maturation of organisms in the context of their evolution as species. For many years, he contributed a monthly column to the magazine Natural History. His essays, written in a lively, conversational style, replete with analogies from his other fields of interest — music, poker and baseball — drew a wide audience. Many of these essays were collected in books such as Ever Since Darwin and The Panda’s Thumbs. Other essay collections included Hen’s Teeth and Horse’s Toes and The Flamingo’s Smile.

In work after work, Gould emphasized the role of chance in the history of life, and argued against the tendency to read the evolutionary record as a story of progress toward some identifiable end. Many characteristics of living things, he noted, arose as by-products of natural selection, not as specific adaptations to environmental circumstances. This placed him in conflict with a school of thought known as selectionism, in which almost all traits are regarded as the result of specific environmental pressures.

In his widely quoted 1979 essay, “The Spandrels of San Marco and the Panglossian Paradigm,” Gould compared the accidentally arising features of living things to spandrels, an incidental feature of Gothic architecture created to connect larger and more essential structural elements. He compared extreme selectionist views to those of the fatuous philosopher Dr. Pangloss in Voltaire’s novel Candide. Controversy over the issues raised by Gould’s essay continues to this day.

Harvard awarded Gould the prestigious Alexander Agassiz Professorship in 1982. That same year, he was diagnosed with peritoneal mesothelioma, an abdominal cancer often linked to asbestos exposure. He was told the median life expectancy for this diagnosis was eight months. He took the opportunity to write an article about the common misunderstanding of median numbers; such an estimate means that half of all diagnosed patients live longer than eight months. With surgery, radiation and chemotherapy, Gould recovered completely and lived for another 20 years. While undergoing the treatment, he reported, he had used marijuana to alleviate his nausea, and later advocated the drug’s decriminalization for this medical purpose.

Despite his involvement in public controversies, Gould never lost interest in the fundamentals of paleontology, the painstaking examination of the fossil record of life on Earth. In his 1989 book, Wonderful Life, Gould explored the mysteries of the Burgess Shale, an exceptionally rich fossil field in the Canadian Rockies. Most fossils preserve only the skeletons or shells of dead creatures. The Burgess Shale is exceptional for its fossil record of the soft tissues of creatures long extinct, some as old as 505 million years.

Through his popular books and frequent television appearances, Gould came to be seen as the public face of evolutionary theory. This eventually drew fire from others in the field, who felt that he represented his own views as those of a larger consensus. His colleagues were quick to support him, however, when he used his public profile to defend the teaching of evolution in public schools after it came under attack from religious fundamentalists. Although some in the anti-evolution camp attempted to exploit conflicts between different schools of evolutionary theory, Gould stressed that all responsible scientists in his field were in agreement on the basic principles of evolution through natural selection. In the media and on the witness stand, he argued against alternative explanations — variously known as creationism, creation science or intelligent design — as lacking any grounding in fact. He did not dismiss the validity of religious belief in other areas, such as morality. He portrayed science and religion as “non-overlapping magisteria,” modes of thought concerned with entirely separate questions, a position that did not entirely satisfy some of his atheist peers, such as the evolutionary scientist Richard Dawkins or philosopher Daniel Dennett.

Throughout the 1990s, Gould continued to speak out on public issues and to explore a variety of scientific and philosophical questions in such accessible books as Full House and Rocks of Ages. Gould long contended that many characteristics of human psychology were by-products of natural selection, rather than adaptations necessary for survival, a position that placed him in conflict with the sociobiology advocated by his Harvard colleague Edward O. Wilson. The school of thought known as evolutionary psychology also finds selectionist explanations for certain aspects of human behavior, a view that Gould resisted. He did not dismiss the idea that some human traits could be attributed to natural selection, but cautioned the public and his fellow theorists from assuming that they were necessary and unalterable. He particularly objected to the attempt by some writers to identify inherent differences in intelligence between the sexes or between human races. In his 1996 book, The Mismeasure of Man, Gould reviewed the history of such thinking, subjecting current efforts in that vein to severe ridicule.

In 1996, Gould was appointed Vincent Astor Visiting Research Professor of Biology at New York University. From then on he divided his time between homes in Boston and New York City. From 1999 to 2001, Gould served as president of the American Association for the Advancement of Science. At the close of his term, the American Humanist Association named him Humanist of the Year. The following year, he publishedThe Structure of Evolutionary Theory, a summary of his view of the subject and its contending schools.

Stephen Jay Gould died at home in New York City in 2002, from a form of lung cancer unrelated to his previous illness. He was survived by his wife, Rhonda Shearer, two stepchildren and two sons from a previous marriage. A selection of his essays was published posthumously as The Richness of Life: The Essential Stephen Jay Gould. Six years after his death, the Linnaean Society of London awarded him the Darwin-Wallace medal. His books remain in print, and around the world he remains the most popular, influential and best-loved author on the subject that fascinated him for all six decades of his too-short, brilliantly productive life.