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amoeban social structure
Mike Lieber (U28550@UICVM.BITNET)
Sat, 4 Mar 1995 10:36:54 CST
I understand that the issue that folks most want to talk about is Robert
Johnson, so I ask your forgiveness for momentarily speaking to another issue.
Vance Geiger's good buddy, the farmer-DJ, got it wrong. Those whiskey suckin'
commode huggin', totally dedicated, gargantuan underachievers are the kind of
folks that will tell you that Bela Fleck is a dandruff shampoo, that Kinky
Freeman is a perverted investment banker from the Bronx, or that Bob Wills is
the father of that nerd who writes for the Washington Post. I can forgive all
that--but amoeban social structure? NEVER!
Biologists and system theorists of all stripes have puzzled for years over the
fact that whenever you get enough amoeba crowded into one place, they always
and automatically form a superorganism called a slime mold. The slime mold
has a clearly differentiated set of parts that operate together in predictable
patterns. There is a stalk that sucks nutrients from the surrounding
environment and transports them up the stalk and into several branches that
form from the stalk. Each of these branches have their own skeletal order,
with several buds along their anterior lengths. The buds are the only part of
the structure that reproduce. After a time, the slime mold breaks up (I don't
know why), and when that happens, each of the constituent ameoba goes back to
being independent organisms.
The slime mold illustrates two major principles of all systemic order--emergent
properties of hierarchical organization and, because the hierarchical ordering
from independent constituents is reversible, the near-decomposability of any
hierarchical system. The slime mold as a system has properties that the amoeba
individually do not have. For example, amoeba take in nutrients by osmosis,
but they only pass on nutrients to other amoeba when they colonize in the
slime mold. All amoeba reproduce, but they only refrain from reproducing when
they are in a slime mold (substituting nutrient transfer for reproduction).
Differentiation of function characterizes only amoeba in a S.M. colony, etc..
Nutrient and waste transport through other amoeba to boundary amoeba is a
property of S.M., not of individual amoeba. These differentiated properties
EMERGE from S.M. organization. Emergent properties is a major focus of
attention in understanding evolution. The near-decomposability of hierarchical
order is an inference inherent in the structure of hierarchical systems. The
lower levels of any hierarchy--its lowest order of components--are always the
most integrated, most stable parts of the system. It is common to see a
system whose higher-level components are damaged just continue functioning,
though without higher level controls. Brain damaged animals can continue
breathing, eating, excreting, etc., while unable to function in ways requiring
higher level integration. Altzheimer's victims are one example. What triggers
the process of colony organization in amoeba is still a mystery, but one that
is very worthwhile solving. The reason it is worthwhile solving has to do with
the same issue of genetically provided means of variability and flexibility
of populations that I talked about in my post on the Human Genome Diversity
Project (and the ancillary issue of seed banks).
Okay, I'm done. Excoriate RJ all you want to, but lay off the amoeba or I'll
send you all a computer virus that makes your computers play John Denver
singing Rock Mountain High over and over, even when you turn the computer off.
Mike Lieber
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