Paleofantasy: What Evolution Really Tells Us About Sex, Diet, and How We Live, by Marlene Zuk, Norton, 304 pages, $27.95

The World Until Yesterday: What Can We Learn from Traditional Societies?, by Jared Diamond, Viking, 499 pages, $36

Modern anthropological research may be settling the great debate between the English philosopher Thomas Hobbes and the French philosopher Jean-Jacques Rousseau. Was the state of nature a "war of every man against every man" in which life was "solitary, poor, nasty, brutish, and short," as Hobbes wrote? Or did "savages" live in utopian bliss, thanks to "the tranquility of their passions and their ignorance of vice," as Rousseau believed?

Two new books, Marlene Zuk's Paleofantasy and Jared Diamond's The World Until Yesterday, examine the data on how hunter-gatherers and subsistence farmers have eaten, loved, socialized, fought, reared children, and lived. Both side mostly with Hobbes.

Yet the books offer a radically split decision on what lessons we can draw from Hobbes' triumph. Zuk, a biologist at the University of California–Riverside, aims at destroying contemporary myths, or as she calls them "paleofantasies," about our Stone Age ancestors. She rejects the idea that there was "a time when everything about us—body, mind, and behavior—was in sync with the environment." For Zuk, anthropological knowledge mainly raises questions about how we moderns should live, without providing much in the way of answers.

Diamond, a geographer at the University of California–Los Angeles, is more prone to prescription. He blends his personal experience of living and working for decades among contemporary subsistence farmers and hunter-gatherers in New Guinea with extensive anthropological and ethnographic data from around the world to draw conclusions about how we moderns ought to function.

Both Zuk and Diamond are unconvinced by Rousseau's notion of the noble savage. In his 1754 Discourse on the Origin and the Foundations of Inequality Among Men, the Frenchman claimed that "more murders were committed in a single day of fighting and more horrors in the capture of a single town than had been committed in the state of nature during entire centuries over the whole face of the earth." But archaeological and modern ethnographic data show that small-scale stateless societies—which were once called "savage" or "primitive"—are far more violent than are modern state societies. To the extent that they are a good proxy for Rousseau's state of nature, they reveal Rousseau to be wrong.

Zuk cites archaeological and ethnographic work finding that 14 percent of deaths in ancient and contemporary pre-state societies resulted from human violence. Diamond notes that while the level of violence varies among traditional societies, it "usually ranks as either the leading cause or (after illness) the second-leading cause of death."

These arguments jibe with the data reported by the Harvard neuropsychologist Steven Pinker in his 2011 book The Better Angels of Our Nature: Why Violence Has Declined (Viking). After examining evidence from 20 sets of archaeological data from all over the world ranging from 14,000 to 700 years old, Pinker reported that societies were very dangerous, with the percentage of human deaths attributed to violence ranging from 60 to 15 percent. Similarly, data from 27 stateless societies studied by modern ethnographers found war deaths averaged 500 per 100,000 people, whereas all deaths from wars, genocides, and man-made famines in modern societies in the 20th century amount to a mere 60 to per 100,000.

"It may astonish you readers, as it initially astonished me," Diamond writes, "to learn that trench warfare, machine guns, napalm, atomic bombs, artillery, and submarine torpedoes produce time-averaged war-related death tolls so much lower than those from spears, arrows, and clubs." So how can this be? Because "state warfare is an intermittent exceptional condition, while tribal warfare is virtually continuous."

Activists on behalf of tribal societies, such as Stephen Corry of Survival International, have pushed back against Diamond, arguing that the researchers he relied upon have jiggered the statistics on violence in ways that flatter moderns. Researchers will continue disagreeing about the extent of violence in traditional societies, but Diamond is correct when he observes, "If scholars have been denying traditional warfare's reality for laudable political reasons, the discovery of the facts will undermine the laudable political goals."

He adds, "The rights of indigenous people should be asserted on moral grounds, not by making untrue claims susceptible to refutation." Meanwhile the balance of the evidence suggests that Hobbes was far more right than wrong when he asserted that life in pre-state societies boils down to "war of every man against every man."

One of the chief paleofantasies that Zuk takes on is the view that modern humans are little more than "cavemen in condos," which is her way of characterizing the claim that we're stuck with the same set of genes as the people who walked out of Africa 60,000 to 40,000 years ago.

In this fantasy, our paleolithic ancestors were perfectly adapted to their environment and we are the ones who are out of place. The agricultural and industrial revolutions, this theory suggests, have created novel environments to which our bodies, brains, and behaviors are maladapted, resulting in increased disease, disorder, and discontent. Relying on recent findings in genetic science, Zuk shows that people, like all other creatures, are constantly evolving and adapting to whatever environments they find themselves in.

For example, Zuk takes on the current paleo-diet fad, in which proponents argue that because our hunter-gatherer ancestors supposedly ate a lot more meat and a lot less starch than we do, we should do likewise. If it was good enough for great-granddaddy Og, it must be good for us. Zuk points out that the diets of various groups of ancient peoples and modern hunter-gatherers vary quite considerably with regard to the relative proportions of how much protein and starches they consumed. In fact, natural selection has inscribed that dietary disparity among groups in our very genomes.

Zuk notes that genetic testing of populations with relatively high and low starch consumption finds variations in the number of copies of a gene for the protein amylase, which aids in digesting starches. About 70 percent of people in high starch populations had at least six copies of the gene, whereas 37 percent of meat-eating populations did. Even more famously, and almost unique among mammals, some 35 percent of the globe's people can digest milk as adults. The ability to tolerate lactose arose and spread between 2,200 and 20,000 years ago.

On the other hand, both Zuk and Diamond are right when they note that modern access to essentially unlimited quantities of salt and sugar is harming people's health in both modern and traditional societies. Diamond observes that the contemporary prevalence of diabetes is considerably lower among the descendants of Europeans than it is among Africans and Asians. He speculates that earlier access to sugar in the West may have generated a background epidemic of diabetes in prior centuries, during which people more genetically prone to the disease had fewer children. Consequently, the modern descendants of those Europeans who survived sugar abundance are today genetically less likely to suffer diabetes.

"No one, whether a low-carb enthusiast, a proponent of bacon fat, or a fan of organic food, can legitimately claim to have found the only 'natural' diet for humans," Zuk writes. "We simply ate too many different foods in the past, and have adapted to too many new ones, to draw such a conclusion." She does hold out the prospect that genetic testing may in the future help guide individuals toward diets that are more suitable.

Some paleo proponents argue that modern life has made us unhealthy compared to our Stone Age forbears. Rousseau certainly agreed, citing "the good constitution of savages" and claiming "they know hardly any sicknesses other than wounds and old age." Rousseau further agreed that modernity has produced diseases: "one could easily produce the history of human illnesses by following the history of civil societies," he wrote.

It is undoubtedly true that the dense settlement made possible by farming and the domestication of animals dramatically sped up the incubation of novel infectious diseases. Many researchers argue that human health suffered with the ancient switch to farming; archaeological research, for example, finds that prehistoric farmers were shorter, suffered more skeletal lesions from hard work, and had worse teeth than did hunter-gatherers.

On the other hand, human populations began to expand with the advent of agriculture, suggesting that the development increased the overall fitness of farmers compared to hunter-gatherers. Farmers had more kids who subsequently lived to reproduce. Recent research by the University at Albany–SUNY anthropologist Timothy Gage also questions the popular theory that ancient farmers died at earlier ages than did hunter-gatherers.

The advent of agriculture and herding pushed the evolution of disease resistance among human populations. Take the CCR5-D gene, which protects those who have it from becoming infected with the HIV virus. Recent research suggests that the CCR5-D gene variant likely evolved in Northern Europe in response to smallpox and was spread throughout Europe by Viking raiders and traders.

What about love and sex? Zuk cites preliminary genetic data from the University of Arizona biologist Michael Hammer showing that more women than men left their genes in succeeding generations. This difference implies that in the past, some men had more access to more women than other men. However, Zuk suggests that polygyny became more prevalent with the advent of farming, while monogamy might have been more the norm among hunter-gatherers.

A 2012 study in The Philosophical Transactions of the Royal Society B noted that the "anthropological record indicates that approximately 85 percent of human societies have permitted men to have more than one wife." Yet in modern times normative monogamy has become dominant around the globe, increasing social peace by reducing competition among men. The researchers further noted, "Compared to monogamous societies, polygamous cultures see more rape, kidnapping, murder, assault, robbery, fraud, child neglect and child abuse."

It is not too far of a stretch to think that although societies practicing marital monogamy are historically fewer in number, their comparatively stronger social solidarity has helped them out-grow and out-compete polygamous competitors. And the spread of monogamy has plausibly contributed to the lower levels of violence in the modern societies.

Meanwhile, "It takes a village to raise a child" is not just a platitude in the lives of people in small-scale societies. Human babies are among the most dependent of all creatures. In traditional societies, mothers are helped by a cadre of sisters, grandmothers, and band members. Among other things, Zuk and Diamond note that infants and small children in tribal societies are in near-constant physical contact with their mothers, can suckle more or less on demand, are weaned only after several years, and sleep with their parents.

Diamond asks modern parents to think about imitating the child-rearing patterns of traditional peoples. Zuk maintains her non-prescriptive stance: "The way we think humans might have evolved is a starting point for asking questions." After all, as Zuk points out, "most children grow up just fine" despite a wide variety of child care arrangements.

History is a record of traditional societies receding as state-based societies expand. Far more often than not, state-based societies advanced by destroying and absorbing traditional groups. But as Diamond notes, people from traditional societies these days generally move toward state-based societies, while practically no one from state-based societies chooses to adopt wholesale traditional ways. Diamond asserts that modern societies have "achieved world dominance not because of their general superiority; but for specific reasons: their technological, political, and military advantages derived from their early origins of agriculture, due in turn to their productive local wild domesticable plant and animal species." This is the famous central assertion in his Pulitzer Prize–winning Guns, Germs, and Steel: The Fates of Human Societies (1997). It's also far too simplistic.

Diamond simply doesn't engage with the notion that development of specific human institutions, such as private property and the rule of law, have enabled a happy portion of the global population to rise above humanity's natural state of abject poverty. His description of trade among traditional societies, in which one group specializes in pottery while another focuses on canoes, completely misses how trade makes both groups better through the higher productivity made possible by pursuing comparative advantage. Diamond characterizes the goal of business transactions in modern societies as winning profits by inflicting losses, missing entirely the fact that modern markets consist largely of world-spanning networks of cooperation.

Zuk concludes, "Change is continuous, and those ancient ancestors encountered changes as well; they domesticated animals, they grew crops, and they dealt with diseases. Change does not have to mean disaster. Sometimes it just creates more change." Our modern societies are still doing all of these things, only faster and better. In other words, change has become progress.