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(CNN) -- In the week that I interview the cognitive psychologist and bestselling author Steven Pinker in his office at Harvard, police release the agonizing recordings of emergency calls made during the Sandy Hook school shootings. In Yemen, a suicide attack on the defense ministry kills more than 50 people. An American teacher is shot dead as he goes jogging in Libya. Several people are killed in riots between political factions in Thailand, and peacekeepers have to be dispatched to the Central African Republic.

In short, it's not hard to find anecdotes that seem to contradict a guiding principle behind much of Pinker's work -- which is that science and human reason are, slowly but unmistakably, making the world a better place.

Repeatedly during our conversation, I seek to puncture the silver-haired professor's quietly relentless optimism. If the ongoing tolls of war and violence can't do it, what about the prevalence in America of unscientific beliefs about the origins of life? Or the devastating potential impacts of climate change, paired with the news -- also released in the week we meet -- that 23% Americans don't believe it's happening, up seven percentage points in just eight months?

I try. But it proves far from easy.

Human nature

At first glance Pinker's implacable optimism, though in keeping with his sunny demeanour and stereotypically Canadian friendliness, presents a puzzle. His stellar career -- which includes two Pulitzer Prize nominations for his books How the Mind Works (1997) and The Blank Slate: The modern denial of human nature (2002) -- has been defined, above all, by support for the fraught notion of human nature: the contention that genetic predispositions account in hugely significant ways for how we think, feel and act, why we behave towards others as we do, and why we excel in certain areas rather than others.

This has frequently drawn Pinker into controversy -- as in 2005, when he offered a defense of Larry Summers, then Harvard's President, who had suggested that the under-representation of women in science and maths careers might be down to innate sex differences.

"The possibility that men and women might differ for reasons other than socialization, expectations, hidden biases and barriers is very close to an absolute taboo," Pinker tells me. He faults books such as Lean In, by Facebook's chief operating officer, Sheryl Sandberg, for not entertaining the notion that men and women might not have "identical life desires." But he also insists that taking the possibility of such differences seriously need not lend any justification to policies or prejudices that exclude women from positions of expertise or power.

"Even if there are sex differences, they're differences in the means of two overlapping populations, so for any [stereotypically female] trait you care to name, there'll be many men who are more extreme than most women, and vice versa. So as a matter of both efficiency and of fairness, you should treat every individual as an individual, and not prejudge them."

The human condition

It is generally assumed that anyone who takes human nature seriously will be a fatalist, and probably politically conservative. If we're pre-wired to be how we are, the reasoning goes, we might as well accept it and give up on hopes of any change. One way of interpreting Pinker's most recent book, The Better Angels of Our Nature, is as an 800-page doorstopper of a riposte to this idea. Not only can we change, but when it comes to arguably the most important measure of improvement -- the violence we inflict on each other -- we actually have changed, to an almost incredible degree.

"I had very often come across the objection that if human nature exists -- including some ugly motives like revenge, dominance, greed and lust -- then that would imply it's pointless to try to improve the human condition, because humans are innately depraved," says the 59-year-old, whose distinctive appearance -- today he is sporting black cowboy boots -- frequently gets him stopped in the street. "Or there's an alternative objection: that we ought to improve our lot, and therefore, it cannot be the case that human nature exists."

Pinker puts all this down to "a fear that acknowledging human nature would subvert any attempt to improve the human condition." Better Angels argues that this is a misunderstanding of what human nature means. It shouldn't be identified with a certain set of behaviors; rather, we have a complex variety of predispositions, violent and peaceful, that can be activated in different ways by different environments. The book's title, drawn from Abraham Lincoln's first inaugural address, is "a poetic allusion to the parts of human nature that can overcome the nastier parts," he explains.

But Better Angels is notable above all for the sheer weight of evidence it amasses, culled from forensic archeology, government statistics, town records, and studies by "atrocitologists" of historical genocides and other mass killings. The book demonstrates that homicides, calculated as a proportion of the world's population at any given point, have plummeted; when you look at the numbers this way, World War II wasn't the worst single atrocity in history, but more like the tenth.

Pinker dwells, in sometimes unnerving detail, on horrifying methods of torture once considered routine. "The Heretic's Fork had a pair of sharp spikes at each end," he writes, in what is definitely not the most appalling passage. "One end was propped under the victim's jaw and the other at the base of his neck, so that as his muscles became exhausted he would impale himself in both places."

"Human nature or no human nature," Pinker says, "it's just a brute fact that we don't throw virgins into volcanoes any more. We don't execute people for shoplifting a cabbage. And we used to."

He offers a multi-pronged explanation for this decline, from the rise of the state and of cities, to literacy, trade and democracy. Whether this constitutes an across-the-board endorsement of scientific rationality may be debated. ("Like other latter-day partisans of 'Enlightenment values'," the critic John Gray wrote, "Pinker prefers to ignore the fact that many Enlightenment thinkers have been doctrinally anti-liberal, while quite a few have favored the large-scale use of political violence.") But it's hard to question the basic finding that your chances of meeting a sticky end, all else being equal, are vastly lower in 2014 than they were in 1014.

If Pinker's message has proved hard for some to swallow, that may be because our standards are improving even faster than our actual behavior, giving the misleading impression that things are getting worse. "Hate attacks on Muslims are deplorable, and they ought to be combated, and it reflects well that we're concerned when they do occur," Pinker says. "But by the standards of past pogroms and ethnic cleansings, they're in the noise: this is not a phenomenon of the same magnitude as the ethnic expulsions of decades past."

We've even witnessed the emergence of whole new categories of condemnable acts. Take bullying, says Pinker: "The President of the United States gave a speech denouncing bullying! When I was a child, this would have been worthy of satire." As we continue to construct a social environment that activates more and more of our peaceable dispositions, and fewer and fewer of our aggressive ones, the remaining instances of bad behavior stick out like ever-sorer thumbs.

What's more, evolutionary psychology, one of Pinker's several specialisms, can explain why. For reasons that long ago made excellent sense, our brains are adapted to focus on bad news over good, vivid threats over vague ones, and recent horrors over historically distant atrocities. Our elevated levels of anxiety about the future might actually be a sign of reason's triumph.

"It could be interpreted as a sign of our growing up," Pinker says. "We worry about more things, because we know that there are more things to worry about. Every time we go to a restaurant, we worry we might be ingesting saturated fats, or carcinogens. For my parents' generation, the main concern about food was: 'Does it taste delicious?'"

The Stuff of Thought

Many of Pinker's most ambitious ideas about science and human morality have their origins in a seemingly trivial observation about irregular verbs. Building on the groundbreaking linguistic ideas of Noam Chomsky, Pinker proposed that certain simple language errors committed by young children "capture the essence of language" itself.

When a three-year-old says "I eated the ice cream" or "we holded the kittens", she is, Pinker observes, following a grammar rule correctly, and making a mistake only because we happen to suspend the rule for those verbs in English. Since she couldn't have learned "eated" or "holded" by simply imitating adult speakers, this points to the presence of innate cognitive machinery -- a "language instinct", to quote the title of Pinker's 1994 book -- that enables a young child to construct novel linguistic forms by following rules.

(Irregular verbs have an even more intimate role in Pinker's life: he met his wife, the philosopher Rebecca Goldstein, through an email exchange after he mentioned her correct use of the past participle "stridden" in his book Words and Rules.)

Years later, in 2007's The Stuff of Thought, he extended this reasoning to the structures of "mentalese," the wordless "language of thought" that he argues we use to think in. When, for example, we use spatial language to talk about time -- as in "a long day," or bringing a meeting "forward" -- might we be relying on an in-built, pre-linguistic tendency to think about the abstract notion of time by analogy to space, something far more concretely graspable to an early human concerned with food, shelter and survival?

This view of the mind -- as a set of modules evolved to confront specific cognitive challenges on the Pleistocene savannah -- is most ambitiously on display in How the Mind Works, a dazzling effort to "reverse engineer" all of our mental capacities, asking for what purposes each might have been selected. Love, humor, war, jealousy, the disgust we feel at the idea of eating certain animals but not others, religious food taboos, compulsive lying: none of them escape the blade of Pinker's rationalist scalpel.

Assuming you buy the book's general approach, it is almost impossible after reading it to cling to the romantic notion that there might be more to our inner lives than the brute facts of biology and natural selection. The notable exception is how the brain causes sentience, or conscious awareness: after a long discussion on the topic, Pinker finally concludes: "Beats me!" There's reason to believe, he argues, that humans may simply lack the mental capacity ever to solve the mind--body problem.

But the broader philosophical question -- how far science can, or should, reach into the life of the mind -- got a disputatious airing last year, when Pinker wrote an essay for the New Republic entitled "Science is not your enemy." It was motivated in part by reports on both sides of the Atlantic about declining student enrolments in humanities subjects, and was Pinker's intervention in the long-running debate over "scientism": are science and scientists guilty of attempting to colonize areas of intellectual life where they don't belong?

Rather than denying that this was a real phenomenon, as numerous scientists have, Pinker audaciously claimed it was a good thing -- providing you defined "scientism" correctly. Humanities scholars had themselves to blame, he implied, for the decline of their fields: by insisting on remaining inside departmental silos, resistant to new approaches, they'd helped guarantee their growing irrelevance. Science was not engaged upon "an imperialistic drive to occupy the humanities," he wrote. "The promise of science is to enrich and diversify the intellectual tools of humanistic scholarship, not to obliterate them."

In a furious response, entitled "Crimes against humanities," the New Republic's literary editor, Leon Wieseltier, accused Pinker of denying the very possibility of valid yet non-scientific knowledge. How absurd, he argued, to imagine that a scientific analysis of a painting -- a chemical breakdown of its pigments and textures, and so on -- could be the only thing worth saying about it. Pinker calls this a "paranoid" interpretation of his argument. "How could an understanding of perception of color, of form, of lighting, of shading, of content such as faces and landscapes not enrich our understanding of art?"

Yet if Wieseltier's retort was overheated, he may still have a point. Pinker wasn't -- and isn't -- merely calling on scholars from different disciplines to talk to each other more. His argument is that any scholar committed to the idea that "the world is intelligible" is doing science. "The great thinkers of the Age of Reason and the Enlightenment were scientists," he wrote, naming various philosophers.

It seems to follow from this that non-scientific scholarship doesn't help make the world intelligible, but Pinker will have none of it. "I'm married to a humanities scholar. I collaborate with humanities scholars. I'm in fields like linguistics, where deans don't know whether it's the humanities or not," he says. "Many humanities scholars -- particularly here at Harvard and MIT, but elsewhere too -- find it very exciting that there might be new ways of approaching old problems, and an influx of new ideas. I mean, who in their right mind could defend insularity as a principle for excellence in anything?"

Of course there are ways of studying a painting, he concedes, that result in worthwhile insights that can't be described as scientific. But, he tells me, "I think the humanities would do themselves a favor by not insisting on staying in a silo. If they are wanting to attract the smartest minds from the next generation, it would be wise to hold out the promise that there will be new ways of understanding things -- the same expansive mindset that attracts smart, ambitious people to the sciences could also attract them to the humanities.

"That it isn't just a question of reinterpreting the same works of art, with the same methods, over and over again," he concludes. "I don't see why humanistic scholarship can't make progress. Wieseltier seemed to insist that it can't, but I don't think most people in the humanities would agree with this. He claims to speak for the humanities. But I can imagine a lot of people in the humanities saying: 'Speak for yourself!'"

Parallel universes

Pinker was born in 1954 in Montreal, and raised in that bilingual city's English-speaking Jewish community (his sister, Susan, is also a psychologist, of the clinical rather than research variety). It's tempting to try to attribute his subsequent intellectual interests to the milieu of his upbringing. Did his focus on language emerge from having grown up in a linguistic battleground? Did his conception of the mind as a complex assemblage of modules, each designed for specific purposes, arise from inspecting the machines his grandfather used as a garment manufacturer? Was it growing up in the 1960s, when many progressives embraced a "blank slate" model of humans as a precondition for radical change, that prompted him to rebel against that notion in his work?

Such speculation can be hazardous when it concerns an evolutionary psychologist who believes that genetic heritage is more important than parenting or peer-group influence. But how far, really, does Pinker believes his career trajectory was influenced by his genes, and how far by his upbringing?

"There are parallel universes to this one [in which] I wouldn't have written The Better Angels of Our Nature or The Language Instinct," he says. "But I'd probably be in the sciences of something human. I probably wouldn't have been a physicist: I'm too much of a yenta, too interested in humans." On the other hand, "I probably wouldn't have been a literary critic."

In this universe, Pinker studied experimental psychology at McGill University in Toronto, then did his PhD in the same field at Harvard; he has spent the rest of his career there and at MIT, just down the street.

Wherever he got them from, Pinker's dispositions include a prodigious appetite for work. As well as being a self-confessed micromanager in his teaching work, as Harvard's Johnstone Family Professor of Psychology, he's usually either pursuing a full schedule of research, speaking and article-writing, or plunging into months-long marathons of book-writing.

"When I write a book, it's almost all-consuming," he says, recalling the year he spent in his house on Cape Cod writing The Better Angels, seven days a week, and sometimes until three in the morning. (He'd spent the previous year doing little but reading in preparation for it.) "I do try to exercise. I try to spend some time being a human being with my wife" -- as recreation, he and Goldstein ride a tandem bicycle and paddle a tandem kayak. "Fortunately, she's also a very intense writer, so she sympathizes."

The couple do not have children, a fact Pinker sometimes uses to illustrate the non-determinative nature of genetic predispositions. (He might be predisposed, thanks to natural selection, to reproduce, but he's used his frontal lobe, a crucial part of his evolutionary inheritance, to decide not to.) "Some things have to give," Pinker says. "I'm not on Facebook, I don't see a whole lot of movies, I don't watch much TV -- not because I consider myself above TV, I just don't have time. And I don't have a whole lot of face-to-face meetings." The Pinker--Goldstein house is sometimes almost silent, except for keyboard-tapping, for days and weeks on end.

Both partners are self-described, out-and-proud atheists. Yet while Pinker has received awards from atheist organizations for his support for their cause, it's notable that he opts not to focus on religion, or its opponents, in his work. A Pinker book on the topic would surely have sold impressively, anointing him the fifth horseman of New Atheism -- but "there's just not enough intellectual content in there, at least on mind, for me to explore," he says. "I think [Richard] Dawkins has done a fine job; I don't think I have anything to add to that."

Pinker's relative lack of engagement in the modern wars over belief shouldn't be taken as any endorsement of Stephen Jay Gould's argument that religion and science are "non-overlapping magisteria", each a legitimate domain of authority that should keep out of the other's business. "As a matter of fact," Pinker says, "religions have concerned themselves with the subject-matter of science... All the world's major religions have origin myths, they have theories of psychology, of what animates a body that allows it to make decisions. And I think science has competed on that territory successfully: it has shown that those explanations are factually incorrect."

Nor, in his eyes, should religion have any franchise on morality: "That's not to say that morality is going to be determined by biology -- it could be -- but rather that it's the subject-matter of secular moral philosophy."

Does any kind of spirituality, however non-religiously defined, play a role in his life?

"I'm afraid of using the word 'spiritual'," he says. "I mean, I have a sense of awe and wonder -- a sense of intellectual vertigo in pondering certain questions. I hesitate to use the word 'spiritual' just because it comes with so much baggage about the supernatural."

Pinker's next book, The Sense of Style, will be a style manual for writers incorporating insights from cognitive psychology and linguistics. For example, it will offer advice on how to get around "the curse of knowledge" -- the difficulty writers face in being unable to place themselves in the mind of a reader who doesn't already know as much as the writer knows. Or the question of how to relate to one's imagined reader: insights from psychology, Pinker will argue, show that the appropriate metaphor to keep in mind is one of vision -- that "the stance you take as a writer ought to be to pretend that you're pointing out something in the world that your reader could see with his own eyes if only he were given an unobstructed view".

To the extent that these, or any other findings, rely on explanations from evolutionary psychology, they're vulnerable to a recurrent criticism: aren't evolutionary psychologists guilty of simply constructing retrospectively satisfying "just-so stories," with no way of showing whether or not they're the truth?

In one memorable passage in How the Mind Works, Pinker suggests that our cultural tendency to reward successful executives (and Harvard academics) with high-floor offices might result from an adaptive preference for good views of the surrounding territory, the better to defend against attackers. But in an alternative world where we rewarded executives with offices in the basement, couldn't you construct a mirror-image explanation, about the benefits of being able to hide out of sight?

For Pinker, the crucial question is whether a hypothesis can be tested. First, he says, you'd have to establish -- by means of psychology experiments, or surveys of property prices -- that there was indeed a culturally widespread, present-day preference for high floors with good views. Then you'd have to scour the historical evidence: for example, data from studies of "tribal warfare, on whether there's been a historically continued preference for high vantage points over bunkers and burrows." Sufficient data showing a preference through history and across cultures, and in contexts of life and death, might amount to good reason to accept your hypothesis.

Once more, Pinker navigates his way through my critique with ease. All attempts to puncture his unique brand of rational optimism -- his confidence that careful scientific thinking, consistently applied, will carry humanity towards a future of reason, peace and flourishing -- end in failure.

Even climate change, that archetypal case of humanity remaining inert in the face of scientific knowledge, doesn't do it. "I think it would be foolhardy to say we'll solve it, but I don't think it's foolhardy to say we can solve it," Pinker says. "History tells us there have been cases in which the global community has adopted agreements to better collective welfare: the ban on atmospheric nuclear testing would be an example. The ban on commercial whaling. The end of piracy and privateering as a legitimate form of international competition. The banning of fluorocarbons."

In this domain as elsewhere, in Pinker's judgement, science plus judicious optimism may yet win the day. Or, as he puts it: "We're not on a trolley-track to oblivion."

Steven Pinker triptych photo courtesy Scott Nobles

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