A leading anthropologist suggests that protohumans tamed themselves by killing off violent males.
 |
| © Antoine Maillard |
By Melvin Konner, The Atlantic
When I was studying for my doctorate, in the late 1960s, we budding anthropologists read a book called Ideas on Human Evolution,
a collection of then-recent papers in the field. With typical
graduate-student arrogance, I pronounced it “too many ideas chasing too
little data.” Half a century and thousands of fossil finds later, we
have a far more complete—and also more puzzling—view of the human past.
The ever-growing fossil record fills in one missing link in the quest
for evidence of protohumans, only to expose another. Meanwhile, no
single line emerges to connect these antecedents to Homo sapiens, whose origins date back about 300,000 years.
Instead, parallel and divergent lines reveal a variety of now-extinct
hominids that display traits once considered distinctive to our lineage.
For example, traces of little “Hobbits”
found in Indonesia in 2003 show that they walked upright and made
tools; less than four feet tall, with brains about a third the size of
ours, they may have persisted until modern humans arrived in the area
some 50,000 years ago.
As data pile up, so do surprises.
Microscopic methods indicate that certain marks on 2.5-million-year-old
bones were probably made by sharp stone tools; scientists had previously
assumed that such tools came later. The dental tartar caked on the
teeth of Neanderthals suggests
that the brawny, thick-boned people (almost-humans on one of the
parallel lines) probably ate cooked barley along with their meat; these
famously carnivorous folks were really omnivores, like us. DNA from tiny
fragments of bone—for instance, the tip of a pinkie many thousands of years old—has
brought to light a whole new humanlike species that once interbred with
us, as Neanderthals did. Charles Darwin drew evolution as a bush, not a
tree, for a reason.
The study of human evolution is by now about much more than bones and stones. In 1965 a remarkable book—Irven DeVore’s collection Primate Behavior (which
led me to study with DeVore)—made what then seemed a radical claim: We
will never understand our origins without intensive study of the wild
world of our nonhuman relatives. A handful of scientists, including Jane
Goodall, set up tents in distant jungles and savannas. Following
monkeys, apes, and other creatures in their habitats, these scientists
turned their notes and observations into voluminous, quantitative data.
DeVore and others devoted themselves just as rigorously to the remaining
human hunter-gatherers, found on every habitable continent except
Europe—our biological twins, living under conditions resembling the ones
we evolved in.
The multifaceted effort was new and
ambitious, but the idea was old. DeVore had hanging in his office an
1838 quote from Darwin’s notebook: “Origin of man now proved … He who
understands baboon would do more towards metaphysics than Locke.” It’s
an aphorism that calls to mind one of my favorite characterizations of
anthropology—philosophizing with data—and serves as a perfect
introduction to the latest work of Richard Wrangham, who has come up
with some of the boldest and best new ideas about human evolution.
In his third book, The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution,
he deploys fascinating facts of natural history and genetics as he
enters a debate staked out centuries ago by Thomas Hobbes and
Jean-Jacques Rousseau (among other philosophers), and still very much
alive today: how to understand the conjunction of fierce aggression and
cooperative behavior in humans. Why are we so much less violent
day-to-day within our communities (in pretty much all cultures) than our
closest primate relatives, chimpanzees, are within theirs? At the same
time, how is it that human violence directed toward perceived enemy
groups has been so destructive?
Wrangham, who teaches biological
anthropology at Harvard, was mentored by both Goodall and DeVore. He
was in a sense working toward this latest venture in his two previous
books, which explore the opposing poles of behavior. Renowned for his
meticulous fieldwork, especially with chimps in Uganda’s Kibale National Park,
Wrangham showed just how common chimp brutality is. Goodall had
acknowledged with frank regret that her beloved chimpanzees could be
quite violent. One mother and daughter killed the infants of other
females in their group. Males often coerced and beat females, and would
sometimes gang up and attack a chimp from another group.
At
Kibale, large groups of chimps range together, and aggression escalates
accordingly. Wrangham observed as these bigger parties of males got
excited and went out on “patrol” in what looked like an organized way:
They walked along their territorial border, attacking lone chimps from
neighboring communities when they came across them en route. In his 1996
book, Demonic Males, co-authored with Dale Peterson, Wrangham
recapped this and other evidence to draw a dire portrait of humanity
(the male version) as inherently violent by evolutionary legacy. Here
was vivid support for a Hobbesian view of human nature, rooted in
genetics.
Wrangham’s 2009 book, Catching Fire: How Cooking Made Us Human, pursued a very different hypothesis. Based on archaeological evidence, he made the case that our ancestors mastered fire much earlier than most of us had believed—perhaps
closer to 2 million rather than 800,000 years ago—which changed
everything for them. In particular, cooking made possible a much more
diverse diet, by allowing the consumption of fruits, leaves, and other
plant foods with toxic potential when eaten raw. It made meat, too,
safer and easier to digest. As a major bonus, fire extended the day into
the night. Given how important we know conversations and stories told around the fire are
to human hunter-gatherers, it’s easy to see how this process could have
accelerated the evolution of language—an essential ingredient for less
physically aggressive interactions.
In his new book, Wrangham
grapples fully for the first time with the paradox of the title. Over
the decades during which he has focused mostly on the dark side of human
nature, evidence has steadily accumulated that humans, from early on in
their development, are the most cooperative species in the primate
world. Put apes and humans in situations that demand collaboration
between two individuals to achieve a goal, as a variety of experimenters
have done, and even young children perform better than apes. Meanwhile,
classic work on chimps has been complemented by new studies of bonobos,
our other close relative. No more removed from us genetically than
chimps are, they are a radical contrast to them, often called the “make
love, not war” species. Some of our nonhuman kin, such fieldwork has
revealed, can live and evolve almost without violence.
Wrangham
draws on this trove of material as he pursues yet another ambitious
hypothesis: “Reduced reactive aggression must feature alongside
intelligence, cooperation, and social learning as a key contributor to
the emergence and success of our species.” (By reactive aggression,
he means attacking when another individual gets too close, as opposed
to tolerating contact long enough to allow for a possible friendly
interaction.) He also applies his evolutionary logic to studies of a
wider array of animals. He dwells in particular on some marvelous
experiments that explore the taming of wild foxes, minks, and other
species by human-directed artificial selection over many generations.
Such
breeding efforts, Wrangham notes, have produced “the domestication
syndrome”: a change in a suite of traits, not just the low reactive
aggression that breeders have deliberately singled out. For instance, in
a fox study begun in Russia in the early 1950s,
the pups in each litter least likely to bite when approached by humans
were bred forward. Yet a variety of other features appeared in tandem
with docility, among them a smaller face with a shortened snout and more
frequent (less seasonally circumscribed) fertile periods, as in some
other similarly domesticated species.
Enter the bonobos, to whom
Wrangham turns as he considers how diminished aggression may have been
selected for in the evolution of humans. Once thought to be a type of
chimpanzee, bonobos are now known to be a different species. The
standard view holds that they separated from chimps 1 to 2 million years
ago, and were isolated south of a bend in the Congo River. Female
bonobos form strong coalitions—partly based on sex with each other—that
keep a lid on male violence. The “trust hormone” oxytocin is released
during female sex: You could say that the partners are high, in both
senses of the word, on trust. Because females run things, males don’t
attack them, and even male-on-male violence is extremely limited.
Bonobos also display the other traits common to the domestication
syndrome, which suggests—as in the case of the foxes—a broad genetic
dynamic at work.
Wrangham accepts the consensus that the
difference between bonobos and chimps is fundamental, genetic, and
evolutionary. His distinctive explanation of the divergence reflects his
training in ecology: He has learned that over many generations,
ecological realities create species-specific behavior. In the case of
bonobos, he suggests, a lush habitat in which they were protected from
competition with either chimps or gorillas gave them the luxury of
decreasing their own reactive aggression. Other examples of nonhuman
self-domestication in the wild exist—for instance, the Zanzibar red
colobus monkey diverged from the mainland African red colobus in similar
ways during its island isolation—but bonobos are the closest and most
relevant to us.
In fact, Wrangham’s notion
of human evolution powered by self-domestication has an ancient
lineage: The basic idea was first proposed by a disciple of Aristotle’s
named Theophrastus and has been debated several times since the 18th
century. This latest version, too, is bound to provoke controversy, but
that’s what bold theorizing is supposed to do. And Wrangham is nothing
if not bold as he puts the paradox in his title to use. In his telling,
the dark side of protohuman nature was enlisted in the evolution of
communal harmony.
Central to his argument is the idea that
cooperative killing of incurably violent individuals played a central
role in our self-domestication. Much as the Russian scientists
eliminated the fierce fox pups from the breeding pool, our ancestors
killed men who were guilty of repeated acts of violence. Certainly
all-male raiding parties have operated in some groups of humans, seeking
out and killing victims in neighboring villages (which recalls the
patrolling chimps that Wrangham reported on earlier in his career). The
twist in his current theory is that such ambushes are turned inward, to
protect the group from one of its own: They serve as a form of capital
punishment. Wrangham cites a number of examples of anthropologists
witnessing a group of men collaborating to kill a violent man in their
midst.
The idea is intriguing, and it is indeed true that human
hunter-gatherers, whose societies exist without governments, sometimes
collectively eliminate bad actors. But such actions are rare, as the
Canadian anthropologist Richard Lee emphasized in his extensive studies
of the !Kung, which include the report of an unusual case: After a
certain man killed at least two people, several other men ambushed and
killed him. My own two years with the !Kung point to a more robust
possible selection process for winnowing out aggression: female choice.
Women in most hunter-gatherer groups, as I learned in the course of my
experience in the field, are closer to equality with men than are women
in many other societies. Evolutionary logic suggests that young women
and their parents, in choosing less violent mates through the
generations, could provide steady selection pressure toward lower
reactive aggression—steadier pressure than infrequent dramas of capital
punishment could. (Female bonobo coalitions would seem primed to serve a
similar taming function.)
Although he downplays such a
comparatively domestic story of self-domestication, Wrangham has
nonetheless highlighted a puzzle at the core of human evolution, and
delivered a reminder of the double-edged nature of our virtues and
vices. “Human nature is a chimera,” he concludes, evoking both the
hybrid monster of mythic lore and the biological phenomenon of
genetically hybrid organisms. In a closing meditation on a 2017 visit to
Poland, he writes, “I walked around Auschwitz. I could feel the chimera
at its best and worst.” Violence and virtue, he recognizes, are not
opposites but powerful, not always reliable allies. “So much
cooperation,” he notes of the smoothly operating human machinery of mass
murder—“it can be for good or bad.” To protect us from danger, which
now arises mainly from our own inclinations and actions, clear-eyed
wisdom like that is surely what we need.
COMMENTS