Genes, Brains, and Human Potential The Science and Ideology of Intelligence

236 POTENTIAL BETWEEN BRAINS

implications. I show how diff er ent social forms have evolved, with diff er-

ent implications for intelligent— including cognitive— systems. Th is

examination provides some of the conceptual grounds for better appre-

ciating human cognitive systems in subsequent chapters.

FROM SINGLE CELLS TO SOCIAL BEINGS

Th e benefi ts of sociality are oft en described quite simply as twofold. First,
it imparts a wider eff ective awareness of things going on in the world (two
pairs of eyes are better than one, etc.). Second, it creates a wider range of
pos si ble responses (two pairs of hands, etc.). Both are particularly
valuable in changeable environments. Such are the conditions that fi rst
brought many bacteria and slime moulds into social groups. Th e theoreti-
cal implications for intelligent systems explain why such groups are
studied so intensively.
One subject of study has been the soil organism Myxobacteria. If nutri-
ents become depleted, individuals start to secrete a mutually attractive sub-
stance. Small molecules called auto- inducers are synthesized in individual
cells in response to the stress warnings. Th ese are then released into the
local medium and bind to receptors on individuals in the neighborhood.
When the concentration of inducers reaches a certain threshold, they
trigger internal signaling and movements that bring the cells together.
In response to this quorum sensing, approximately one hundred thou-
sand cells aggregate to form a single fruiting body. Continuing waves of
intercellular signaling orchestrate recruitment of numerous genes to
produce new cell components. Extensive morphological and biochemi-
cal changes follow in the cells, and thick- walled spherical spores are
formed on, and shed from, the fruiting body. Th ese are sessile and resis-
tant cells that can withstand starvation until nutrients reappear.
Th is is, of course, analogous to the use of morphogens in multicellular
organisms for coordinating diff erentiation and development. As with
development, the functioning of those signals depends on the statistical
structure— their distribution in space and time— not just concentration.
Indeed, up to twenty chemically distinct signals are used in the micro-
organism’s response to stress. And these signals must be integrated to

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