January 2012, Week 4


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Sat, 28 Jan 2012 07:43:07 -0500
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[For a four minute documentary narrated by the co-author
of this research, Coren Apicella, go to the source link
below. -- moderator.]

Dawn of Social Networks

by Jake Miller
January 25, 2012
Focus (Harvard Medical, Dental and Public Health Schools)

Ancient humans may not have had the luxury of updating
their Facebook status, but social networks were
nevertheless an essential component of their lives, a
new study suggests.

The study's findings describe elements of social network
structures that may have been present early in human
history, suggesting how our ancestors may have formed
ties with both kin and non-kin based on shared
attributes, including the tendency to cooperate.
According to the paper, social networks likely
contributed to the evolution of cooperation.

"The astonishing thing is that ancient human social
networks so very much resemble what we see today," said
Nicholas Christakis, professor of health care policy
(medical sociology) at Harvard Medical School and
professor of sociology in the Harvard Faculty of Arts
and Sciences, and senior author on the study. "From the
time we were around campfires and had words floating
through the air, to today when we have digital packets
floating through the ether, we've made networks of
basically the same kind."

"We found that what modern people are doing with online
social networks is what we've always done-not just
before Facebook, but before agriculture," said study co-
author James Fowler, professor of medical genetics and
political science at the University of California, San
Diego, who, with Christakis, has authored a number of
seminal studies of human social networks.

The findings will be published January 26 in Nature.

Roots of altruism

The natural world, red in tooth and claw, has a gentle
side. While individuals compete fiercely to ensure the
proliferation of their progeny, a few animals, including
humans, also cooperate and act altruistically.
Researchers have wondered if human social networks are a
product of modern lifestyles, or if they could have
emerged under the kind of conditions that our distant
ancestors faced. This question has been challenging for
classic evolutionary theory to explain neatly.

For cooperation to arise, an altruistic act, like
sharing food with a non-relative, must have a net
benefit for the sharers. Otherwise, purely self-serving
individuals would outcompete and eventually replace the
selfless. All theoretical explanations for the evolution
of cooperation-kin selection, reciprocal altruism, group
selection-rely on the existence of some system that
allows cooperators to group together with other
individuals who tend to share.

"If you can get cooperators to cluster together in
social space, cooperation can evolve," said Coren
Apicella, a post-doctoral research fellow in Health Care
Policy at Harvard Medical School and first author on the
paper. "Social networks allow this to happen."

While it is not possible to quiz our distant ancestors
about their friendships or habits of sharing and
collaborating, a team of researchers from Harvard
Medical School, the University of California, San Diego,
and the University of Cambridge have characterized the
structure of social networks among the Hadza, an ethnic
group in the Lake Eyasi region of Tanzania, one of the
last surviving groups of hunter gathers. (There are less
than 1,000 Hadza left who live in the traditional way).

Getting connected

The Hadza lifestyle predates the invention of
agriculture. The Hadza eat a wide range of wild foods,
foraging for tubers, nuts, and fruit and hunting a great
variety of animals, including flamingos, shrews, and
giraffes. Honey is one of their favorite foods, known by
half a dozen different names in Hadzane, their primary

Apicella took the lead in collecting the data for the
study, interviewing 205 adult Hadza over the course two
months, measuring their tendency to cooperate and
mapping their friendships.

Apicella, Fowler and Christakis designed the study and
experiments, working with Frank Marlowe, lecturer in the
Department of Archaeology and Anthropology of the
University of Cambridge, and author of the only book-
length ethnography on the Hadza in English.

Collecting the data was not easy. The nomadic Hadza roam
over 4,000 rugged square kilometers. Apicella and her
research assistants travelled the region by Land Cruiser
battling mud-drenched trails-at one point forcing her
and her colleagues to pave the ground with felled trees-
and, on an earlier trip, even fleeing a horde of
marauding elephants.

In order to construct a social network, Apicella and her
colleagues took a dual approach.  First, they asked
Hadza adults to identify individuals they would prefer
to live with in their next encampment. Second, they gave
each adult three straws of honey and were told they
could give these straws as gifts to anyone in their
camp. This generated 1,263 campmate ties and 426 gift

In a separate activity, the researchers measured levels
of cooperation by giving the Hadza additional honey
straws that they could either keep for themselves or
donate to the group.

When the networks were mapped and analyzed, the
researchers found that co-operators and non-cooperators
formed distinct clusters.

The researchers also measured the connectedness of
people with similar height, age, handgrip strength,
etc., and other characteristics, such as food
preference. They also analyzed the transitivity of
friendship-the likelihood that one's friends are friends
with one another, and other network properties.

The structure and dynamics of the Hadza hunter-gatherer
social networks were essentially indistinguishable from
existing social network data drawn from modern

"We turned the data over lots of different ways," said
Fowler. "We looked at over a dozen measures that social
network analysts use to compare networks and pretty
much, the Hadza are just like us."

"Human beings are unusual among species in the extent to
which we form long-term, non-reproductive unions with
other members of our species," said Christakis. "In
other words, not only do we have sex, but we also have

Previous work by Christakis and Fowler, who are
coauthors of the book "Connected," has shown that our
experience of the world depends on where we find
ourselves within social networks. Particular studies
have found that networks influence a surprising variety
of lifestyle and health factors, such as how prone you
are to obesity, smoking cessation, and even happiness.

For the researchers, the Hadza offer strong new evidence
that social networks are a truly ancient, perhaps
integral part of the human story.

This research was funded by the National Institute on
Aging and by the Science of Generosity Initiative of the
University of Notre Dame.


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