Iain Couzin, a British scientist, serves as one of the directors at...
Edmund Selous had an interesting career, and while it started as a ...
> "Such group behaviour holds clues about the evolution of socialit...
J. KAPUSTA/IMAGES.COM
Iain Couzin
In 1905 the field naturalist Edmund Selous,
a confirmed Darwinian and meticulous
observer of bird behaviour, wrote of his
wonderment when observing tens of thou-
sands of starlings coming together to roost:
“they circle; now dense like a polished roof,
now disseminated like the meshes of some
vast all-heaven-sweeping net...wheeling,
rending, darting…a madness in
the sky”.
Throughout his life Selous strug-
gled to explain the remarkable syn-
chrony and coherence of motion
during flocking, and he concluded
that somehow a connectivity of
individual minds and transference
of thoughts must underlie such
behaviour. “They must think col-
lectively, all at the same time, or
at least in streaks or patches — a
square yard or so of an idea, a flash
out of so many brains”.
We now know that such synchro-
nized group behaviour is mediated
through sensory modalities such as
vision, sound, pressure and odour detec-
tion. Individuals tend to maintain a per-
sonal space by avoiding those too close to
themselves; group cohesion results from a
longer-range attraction to others; and ani-
mals often align their direction of travel
with that of nearby neighbours. These
responses can account for many of the
group structures we see in nature, including
insect swarms and the dramatic vortex-like
mills formed by some species of fish and
bat. By adjusting their motion in response
to that of near neighbours, individuals in
groups both generate, and are influenced
by, their social context — there is no cen-
tralized controller.
But when observing a starling flock, or
a sweeping, twisting school of tiny silvered
fish, I often think of Selous’s concept of a
collective mind. It is perhaps too easy to
disregard his vision, based as it was on
a Victorian fascination with telepathy.
Indeed, his rich descriptions capture the
essence of something more, something
we still know very little about: how social
interactions affect the way animals within
highly coordinated groups acquire and
process information.
For individuals within groups, survival
can depend critically on how local behav-
ioural rules scale to collective properties.
Pertinent information, such as the location
of resources or predators, may often be
detected by only a relatively small propor-
tion of group members due to limitations
in individual sensory capabilities, often
further restricted by crowding. Close
behavioural coupling among near neigh-
bours, however, allows a localized change
in direction to be amplified, creating a
rapidly growing and propagating wave
of turning across the group. This positive
feedback results from the ability of indi-
viduals to influence and be influenced by
others, and allows them to experience an
‘effective range’ of perception much larger
than their actual sensory range.
The scaling from actual to effective
sensory range is non-linear, however. It
is hard for groups to remain cohesive and
for information to spread if individu-
als respond only to others very close to
themselves. As sensory range is increased,
a response to a greater number of neigh-
bours increases cohesion and allows effec-
tive long-range transfer of directional
information. If this range expands further
still, groups that form are highly cohesive
but individuals may get misdirected, as the
motion of distant individuals is less likely
to encode relevant information about
localized stimuli.
Individuals within groups may modify
their interactions in a context-dependent
way. Under threat of attack, for example,
individuals often align more strongly with
one another, heightening collective sensi-
tivity to weak or ambiguous environmen-
tal stimuli, and so increasing the ‘system
gain’. However, amplification can occur in
response to random fluctuations, creating
false alarms that can be costly.
Under different circumstances individ-
uals may adopt behaviour that facilitates
collective damping of local fluctuations.
During long-distance migration, for
example, animals are often faced with
the challenge of navigating up noisy and
weak thermal or resource gradients. Local
variability makes this task difficult, or
even impossible, for individuals in isola-
tion. But coherent social interactions can
allow groups to function like an integrated
self-organizing array of sensors, again
increasing effective perceptual range. As
long as interactions are sufficiently sen-
sitive to ensure cohesion, but not
too sensitive to local fluctuations
and individual error, individuals
can effectively respond to the weak
long-range gradient.
We are beginning to comprehend
more fully how individuals in groups
can gain access to higher-order col-
lective computational capabilities
such as the simultaneous acquisition
and processing of information from
widely distributed sources. Group
members may come to a consensus
not only about where to travel but
also about what local rules to use.
Thus, like the brain, groups may
adapt to compute ‘the right thing’ in
different contexts, matching their collective
information-strategy with the statistical
properties of their environment.
Selous wrote in despair of his contem-
poraries’ lack of interest in flocking: “If
there really were anything extraordinary
in the collective movements of birds…they
would have been much discussed and
much wondered at”. But today there is a
rapidly expanding and vibrant community
of biologists, engineers, mathematicians
and physicists for whom flocking serves
as inspiration. Such group behaviour
holds clues about the evolution of social-
ity, and also for the development of novel
technological solutions, from autonomous
swarms of exploratory robots to flocks of
communicating software agents that help
each other to navigate through complex
and unpredictable data environments. ■
Iain Couzin is in the Department of
Zoology, University of Oxford, Oxford
OX1 3PS, UK.
FURTHER READING
Conradt, L. & Roper, T. J. Trends Ecol. Evol. 20, 449–456
(2005).
Couzin, I. D. & Krause, J. Adv. Study Behav. 32, 1–75 (2003).
Couzin, I. D., Krause, J., Franks, N. R. & Levin, S. A. Nature
433, 513–516 (2005).
Sumpter, D. J. T. Phil. Trans. R. Soc. B 361, 5–22 (2006).
For other essays in this series, see http://
nature.com/nature/focus/arts/connections/
index.html
Collective minds
By tapping into social cues, individuals in a group may gain access to higher-order computational
capacities that mirror the group’s responses to its environment.
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NATURE|Vol 445|15 February 2007
CONNE CTIONS
Putting the pieces together
ESSAY
Iain Couzin, a British scientist, serves as one of the directors at the Max Planck Institute of Animal Behavior in the Department of Collective Behaviour. He also holds the position of chair for Biodiversity and Collective Behaviour at the University of Konstanz in Germany. His research focuses on the study of collective behaviour in animals, exploring the key patterns that drive its evolution across various species, including insects, fish, and primates.
Background: https://en.wikipedia.org/wiki/Iain_Couzin
> "Such group behaviour holds clues about the evolution of sociality, and also for the development of novel technological solutions, from autonomous swarms of exploratory robots to flocks of communicating software agents that help each other to navigate through complex and unpredictable data environments."
Edmund Selous had an interesting career, and while it started as a conventional naturalist, he later developed a hatred of the killing of animals for scientific study and pioneered bird-watching as a method of scientific study.
In his book *Bird Watching* (1901) he said:
>For myself, I must confess that I once belonged to this great, poor army of killers, though happily, a bad shot, a most fatigable collector, and a poor half-hearted bungler, generally. But now that I have watched birds closely, the killing of them seems to me as something monstrous and horrible; and, for every one that I have shot, or even only shot at and missed, I hate myself with an increasing hatred. I am convinced that this most excellent result might be arrived at by numbers and numbers of others, if they would only begin to do the same; for the pleasure that belongs to observation and inference is, really, far greater than that which attends any kind of skill or dexterity, even when death and pain add their zest to the latter. Let anyone who has an eye and a brain (but especially the latter), lay down the gun and take up the glasses for a week, a day, even for an hour, if he is lucky, and he will never wish to change back again. He will soon come to regard the killing of birds as not only brutal, but dreadfully silly, and his gun and cartridges, once so dear, will be to him, hereafter, as the toys of childhood are to the grown man.
For more: https://en.wikipedia.org/wiki/Edmund_Selous