Russell H. Tuttle figures he worked on his new book, in one way or another, for 30 years. Apes and Human Evolution, due out February 17, reflects decades of research and teaching that have left a deep imprint on anthropology.

Tuttle has studied the famous 3.6-million-year-old humanlike footprints in Laetoli, Tanzania, and he has measured the soles of living human subjects in the Amazon. For more than two decades he edited the International Journal of Primatology, and in the classroom, he has shaped the critical faculties of contemporary leaders in multiple branches of anthropology.

A “four-field trained” anthropologist—biological, cultural, linguistic, and archaeological, something of a rarity today—Tuttle has never felt comfortable within confining disciplinary and ideological boundaries. “I’m supposed to be just a functional morphologist and sometime paleoanthropologist, dealing with physical stuff, but in fact I’ve always been interested in who and what we are,” he says. “That’s why I’m an anthropologist.”

In his book, as he has throughout his career, Tuttle extracts data from fragmentary remnants in the fossil record and competing scientific interpretations to address a big question: “What makes us human?” He sums up his answer with an illustration intended to be the last word—literally—in Apes and Human Evolution. But a Harvard University Press policy against ending a book with artwork required the image to be set on the next-to-last page.

Figure 13.4, titled “In Conclusion,” shows a bonobo on the left and a human on the right. A bubble above the bonobo reads, “We feel, fear, and think.” Above the person: “We feel, fear, think, and believe.”

“That’s the whole conclusion of the book,” says Tuttle, who rejects a commonly held notion in evolutionary biology that equates humans and apes. The symbolic language unique to Homo sapiens, he writes, makes it possible “to convey information and to share ideas and beliefs”—the basis of human culture. Morality and ideology emerge from that cultural framework, shaping political, spiritual, moral, and social notions, which make up the belief systems that define human life. By contrast, Tuttle adds, “no one has shown that chimpanzees in nature have pervasive shared symbolically mediated ideas, beliefs, and values.”

He doesn’t dispute the genetic relationship between apes and humans as evolutionary biology and anthropology understand it—“I’m very comfortable,” he says, “with coming out of whatever animal background there might be”—but he laments the use to which the common lineage has been put. Tuttle takes particular exception to the assertion as an argument for the protection of apes because it elevates them above other species he deems worthy of the same consideration. Activists, he says, are “trying to emphasize the fact that [apes] have rights just like we do, that they shouldn’t be mistreated.” Tuttle shares the objective of preventing mistreatment, describing human actions toward apes as an “ongoing holocaust,” just not the underlying reasoning. “It’s not because they’re like us; it’s because we are what we are.”

We are, Tuttle writes, “the only extant beings capable of moral and immoral acts,” a distinction that carries a responsibility to respect and protect all species on the planet, not a select few based on genetic similarities. Apes are amoral and therefore blameless for discarding behavior that might appear selfless or cooperative in the interest of individual survival. “The minute the situation changes,” Tuttle says, “they’re out to realize their own breeding potential or their own just subsistence potential.”

The belief systems that define human life, Tuttle adds, are “luxuries” of an existence not based, like that of the apes, primarily on survival. Humans have culturally prescribed limits on behavior and the cognitive capacity to recognize the effects of their actions on others.

Tuttle writes approvingly of New Zealand psychologist Michael C. Corballis’s idea that recursion—the ability to perceive not only our own inner lives but those of others—is a key characteristic separating Homo sapiens from all other species. The author of The Recursive Mind: The Origins of Human Language, Thought, and Civilization (Princeton University Press, 2011), Corballis argues that many species have a “zero-order theory of mind”—that is, the ability to think, know, perceive, or feel. Only humans have the recursive “first-order theory of mind,” which Tuttle describes as “thinking, knowing, perceiving, or feeling what others are thinking, knowing, perceiving, or feeling.”

To illustrate the unique human level of recursion, he quotes Prince Geoffrey from James Goldman’s 1966 play The Lion in Winter, discussing with Queen Eleanor the actions of King Henry II toward his sons. “I know. You know I know. I know you know I know. We know Henry knows, and Henry knows we know it. We’re a knowledgeable family.”

Often Tuttle finds himself in the breach between what we know and what we think we know. After the 1978 discovery of the Laetoli footprints, for example, many scientists believed that they were made by an Australopithecus afarensis, a chimp-like hominid known for the partial skeleton Lucy, found four years earlier by a group including paleoanthropologist Donald Johanson, AM’70, PhD’74. The similarities—of age (about 3.6 million years old) and East African location—were tantalizing, suggesting an evolutionary connection between Lucy, believed to walk upright, and later humans. “People were desperate to link Lucy to the Laetoli footprints,” says Dartmouth anthropologist Nathaniel Dominy, who worked with Tuttle a decade ago as a UChicago postdoc.

Tuttle studied the prints at the request of the late Mary Leakey, who led the team that discovered and excavated them. He deemed the Laetoli footprints incompatible with Lucy’s species, a finding “inconceivable to many researchers” at the time, Dominy says.

Tuttle determined that they were from a humanlike foot of another, indeterminate species. “What that creature was above the ankles, God knows. In fact, I don’t think it would look very much like a modern human, but [its humanlike footprint] makes perfect sense,” Tuttle says. “We know this from animals in general. The first thing that selection is going to act intensively upon are the things in contact with the substrate”—the surface that they walk on. “They have to fit the substrate. You’ve got to be able to be mechanically adapted.”

If not for their age—orders of magnitude older than the previously oldest known footprints of human ancestors—“we would readily conclude that they were made by a member of our genus, Homo,” Tuttle wrote in a 1990 Natural History paper. Associating the prints with the likes of Lucy was a “loose assumption” that should be discarded.

“Rather than caving in to what was popular,” Dominy says, “he staked out a position based on where the evidence took him.” Conflicting interpretations about the source of the Laetoli footprints persist, but support for Tuttle’s position has increased—“more right than wrong,” is his self-assessment. “He stirs the pot,” Dominy says, “and that’s good.”

On a darkening late afternoon in November, as Hyde Park’s first snowfall of the season coats parked cars and piles of fallen leaves, Tuttle sits at home in front of a fire, warming up.

He mentions that he’s 74 and describes some of the ailments that accompany his age. In April he will receive the Charles R. Darwin Lifetime Achievement Award from the American Association of Physical Anthropologists, recognizing 50 years of accomplishments in what Dominy calls “very understated” career.

Offering wine and cheese, Tuttle is gentle and welcoming, but there’s nothing retiring about him—in any sense of the term. He unspools provocative opinions about disparate topics that surface, submerge, and bob up again, cohering into a broad social and scientific critique. Discussing Apes and Human Evolution, he offers a glimpse into the breadth of his thought, from God and race to kinship and love.

Race, he insists, does not exist, an assertion he details in the book. “Anthropologists and human biologists have failed dismally in their attempts to subdivide Homo sapiens into subspecies (called races),” Tuttle writes, “largely because of the prehistoric and historical global admixture among the great variety of people who grace the planet and the disagreements on which features should be used to classify them.”

He has similar problems with religion, specifically what he derides as “politicized spirituality,” yet he’s a churchgoer, even singing in the choir. “I’m a practicing Christian in my own way, but I would never have survived with my views,” Tuttle says. “I don’t believe in heaven and hell, I don’t believe in any of it. I just find that communion is helpful to connect with souls past, present, and future.”

In his own field, when research lapses into what he calls the search for superlatives—the biggest, the earliest, the most recent—he trains a particularly skeptical eye. And as editor in chief of the International Journal of Primatology from 1988 to 2010, Tuttle stood at the barricades, trying to prevent misused language and exaggerated interpretations from inflating facts. When colleagues claim to “reconstruct” species from incomplete bits of fossils, for example, he bristles. Fragmentary information almost never supports such a claim. “You’re not reconstructing,” Tuttle says, “you’re modeling it, at best.”

In Apes and Human Evolution, Tuttle raises these ideas and more, presenting detailed evidence and challenging received wisdom. Into his synthesis of research and theory, weighty with data, he also flashes an occasional light touch, like the quote from The Lion in Winter or a reference to the “fruity faux pas” in the Garden of Eden.

A nod to pop culture can reinforce a point. Tuttle’s identification of human beings as a unique species, for example, is not meant to assert superiority over others. But human actions, to his disappointment, often reflect such hubris. “Sadly, over the past millennium, Earth has become the Planet of People,” he writes, “where far too many individuals and societies behave like the omnipotent beings in Pierre Boulle’s Planet of the Apes.”

Discursive references like those, combined with the scholarship and skepticism at its heart, make reading Tuttle’s book feel like sitting in on a class. “It very much reminded me of his lectures,” Dominy says. “I could almost hear him read those words.”

For all the influence of his half century of fieldwork and research, Tuttle considers teaching his true calling. “It’s not my whole life,” he says, “but it is my life.”

During what he describes as a “challenging childhood” in rural Ohio, Tuttle found role models in his teachers. He considered himself better suited to work with older students, so he decided he should become a college professor.

After completing a master’s degree at Ohio State and a PhD from Berkeley in 1965, he came to Chicago, where his intuition about teaching has proven true. A winner of the McGraw Hill Award for Excellence in Undergraduate Teaching from the American Anthropological Association in 2003 and of the University’s Quantrell Award in 2006, he has long been a sought-after professor.

Whatever the specific subject matter, Tuttle teaches “a sense of criticism. Don’t accept anything.” Anthropology provides a perfect crucible in which to forge that lesson. “Questions of human evolution and our place among organisms are excellent challenges to one’s ability to think critically,” he writes in Apes and Human Evolution, “and to assist students who wish to learn how to think critically instead of merely being titillated and told what to think.”

Tuttle might not titillate his students, but he knows how to entertain them. Vivek Venkataraman, AB’07, was a physics major and philosophy minor who wanted to study something different in his final months before graduating. “I was writing up a bachelor’s thesis in physics, and I wanted to take a course that was just totally outside my zone of familiarity,” Venkataraman says, “and Russ’s classes are legendary.”

He signed up for Tuttle’s celebrity science course, an introduction to doubt, to the responsibility to value and evaluate evidence above all. Students puzzle over the work of famous anthropologists, many of whom Tuttle has known. At the end of the quarter, they receive a list of names with the question, “Is this person more of a celebrity or more of a scientist?”

“He wanted us to decide based on what we’ve read in the course,” Venkataraman says. “I think that’s such an important critical-thinking skill to develop in this day and age when we’re faced with so much information. How do you separate the good from the bad?”

That’s a perpetually open question, but Tuttle’s course gave Venkataraman an unambiguous answer to a different question. He realized he wanted to be an anthropologist. Now a PhD student at Dartmouth, he credits Tuttle for both his initial interest in the field and his ability to advance in it. “Russ was really instrumental to me personally in helping me follow that career path that I didn’t really have any formal training in,” Venkataraman says.

Tuttle relishes the opportunity to help his students. In his office one November afternoon, he chatted over a pick-me-up cup of coffee, occasionally glancing at his computer to check e-mail. When a message came informing him that a fourth-year he had recommended had received a Gates Cambridge Scholarship, he beamed, the lingering fatigue he’d mentioned moments earlier gone in a mouse click.

A few days later, on a Saturday afternoon, Tuttle’s doorbell rang. Outside stood a former student who had gone into the Navy. He came to thank his old professor for helping him save a lower limb, and maybe the life, of a fellow sailor. “Because when I taught him the anatomy, chimp anatomy, I apparently had dissected a chimp in front of them,” Tuttle says, “and, just as an aside, showed where you would apply pressure, the femoral artery.”

In the ambitions and accomplishments of his students, Tuttle finds nothing less than hope for humanity. “I can be very negative,” he says, recalling slights in his academic career and dispiriting public acts—he mentions drones more than once. But optimism about human potential peeks through when he talks about the inherent fairness and reciprocity seen in babies, and especially the way those qualities flourish in so many young adults he teaches. “It’s astounding, absolutely astounding what our undergrads, many of them, do,” he says. “These quiet people, they’re working in labs, they have wonderful aspirations—reasonable aspirations and they’re critical of them—they do community service in sometimes what I would call very dangerous situations.” And, he notes, many come from circumstances that are, if not dangerous, at least disadvantaged. “I don’t know how they deal with it.”

Students he taught decades ago are equally effusive about Tuttle’s influence on them. His legacy spans disciplines and generations. “Because he was an integrative researcher in the 1960s, he has produced many of the major players,” Dominy says. “In a family tree of the discipline, his position would be a large central node with many descendants,” including Boston University’s Matt Cartmill, AM’66, PhD’70; Duke University’s Ken Glander, AM’71, PhD’75; and the University of Calgary’s Benedikt Hallgrimsson, AM’90, PhD’95.

Tuttle wanted to make an impact across cultural borders as well. Establishing an undergraduate program in Tanzania in the late 1990s through the Associated Colleges of the Midwest, he broadened the educational experience for American students and also created opportunities for locals. “I wanted to have an indigenous African paleoanthropology,” he says. “Instead of people going in there from Britain and the United States and taking out the intellectual heritage, have them in charge of it.”

The impulse came from a “missionary spirit,” Tuttle says, a disposition that could apply to his approach to his teaching in general. Dominy once stumbled across an essay collection in the Seminary Co-op on the mechanisms of learning, which made a distinction between education and instruction. Instruction, “to put into the structure,” is about input, a utilitarian transfer of information. Education—derived from the Latin educare, meaning “from within”—requires students to be active participants. Educators encourage them to process and integrate facts to develop an independent understanding. “Nobody,” Dominy says, “exemplified that principle better than Russ Tuttle.”

In his relationships with students, Tuttle exemplifies what he considers another essential facet of humanity: kinship. Kinship that goes beyond genetic or geographic links to include numerous categories of our own devising, groups that Tuttle’s UChicago colleague Marshall Sahlins describes as “persons who participate intrinsically in each other’s existence; they are members of one another.”

They might be family only in a figurative sense, but the connections often run deeper than blood. “Sports teams; military units; firefighters; police squads; gangs; religious groups; gay, lesbian, and transgendered couples; and communities and other affiliatively bonded people commonly employ kinship terms to refer to one another,” Tuttle writes.

Love, in its various forms, helps hold the groups together. “I have a piece in there, ‘What’s Love Got to Do with It?’” he says. “And I come right up front and say, a great deal,” including a great deal of the difference he identifies between humans and other species.

As intimate as chimpanzees can appear to be, for example, Tuttle says they are bound more by circumstance than emotion—and in the wild the circumstances can change suddenly and violently. “It’s remarkable how you see these chimpanzee males, how they’re all buddy-buddy, when something happens they hug each other, they hold each other’s penises, of all things. You talk about trust and reassurance and that kind of thing,” he says. “But no, no, if one gets injured, the alpha male, look out, the minute he shows weakness, he’s in for quite a trial.”

Comparable behavior can be observed among females. “They can look like they’re very close kin, they groom each other, this, that, and the other, but really it’s not the same thing as humans,” he adds. “It’s just what you’re used to. They’re used to one another and the relationships develop, but I don’t think there’s love involved. There’s very little love to spare there if it becomes competitive.”

Conflict arises among humans, of course, often resulting in emotional or physical damage, but the phenomena of kinship and love can preserve or repair bonds in a way that doesn’t happen with animals. “Only we have these really long-lasting love relationships,” Tuttle says, that “prevail over all kinds of awful things that families do to each other.”

Human morality, another distinguishing characteristic in Tuttle’s estimation, acts as a behavioral restraint. Respect can transcend opposing priorities and opinions, for example, with the recursive order of mind unique to humans fostering understanding across divisions.

Perhaps even more daunting than the question of what makes us human is the unsolved mystery of when Homo sapiens emerged. “That’s a real tough one,” Tuttle says, noting that many humanlike species failed to survive. Small and relatively defenseless creatures—“they certainly weren’t out there at the top of the food chain, believe me, for a long, long time”—early humans needed to become cooperative.  “I think the real break was when it was found useful, for survival, to be able to somehow accept nongenetic kin into the group. To really start a kind of bonding, a give and take, that’s not based totally on teeth and jaws or clubs and stuff like that.”

Based, instead, on what we might recognize as a human belief system, on something more like love. “Isn’t that the bottom line?” Tuttle says. “Isn’t that the thing that makes us quite different?”

Tuttle’s answer goes unsaid, but it’s fitting that he phrased the issue in the form of a question. As his career has illustrated, another defining human characteristic is the quest to understand the mysteries of existence. “We should consider ourselves most fortunate to have faculties that allow us to investigate other natural phenomena and ourselves,” he writes. “Collectively and individually, we not only possess great stores of knowledge but also relentless curiosity about many worldly and spiritual puzzles that invite boundless exploration.”