Emergent Properties in Biology

Here's one of my old Usenet postings. I re-discovered this while restoring a bunch of archived files to a new hard disk after a recent crash. After ten years, I still think this was one of my more lucid efforts to explain what was then and is still, a complicated field. The article has been quoted several times in various settings. Feel free to quote it if you like, but don't pretend you wrote it :-)
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Newsgroups: talk.origins
From: dtinker@gpu.utcs.utoronto.ca (David Tinker)
Subject: Emergent Properties. I. Introduction
Organization: University of Toronto, Biochemistry
Date: Wed, 11 Nov 1992 15:50:22 GMT

The recent spate of articles in talk.origins on "emergent properties"
generated some heat, but not much light!  My colleague, Larry Moran,
objects to the term because he suspects (wrongly) that it is based on
non-mechanistic or vitalistic superstition, and (rightly) that the term
implies there is an obstacle to the reductionist agenda in biology.
Other postings imply that the term "emergent properties" is tautologous,
and not unique to biology;  it has been claimed that everything has emergent
properties, so the adjective "emergent" is meaningless.

I think the topic is worth further exploration, and submit this article to
stimulate discussion.  I hope that we have not seen the last word on this
topic.

First, I do not think there is a satisfactory closed definition of the term
"emergent", nor is it universally used by the research school most concerned
with such properties, the 'Artificial Life' community.  Nevertheless I
believe the concept is so well accepted in this community that the term can
be used casually with the assurance that it is understood.  I turned to my
well-thumbed copy of "Artifical Life I" and searched in the annotated
bibliography and in the index for terms like "emergent" - see below for the
results.  Nowhere did I find a definition that would satisfy Larry Moran, but
in re-reading the articles I found many clues to a definition.  So, being
willing to be called a fool, I will essay a definition:

=============================================================================
A system may be said to possess "emergent properties" when (a) it is composed
of a collection of entities, (b) it has global properties, obeying well-
characterised rules that may be used for predictive purposes, that arise from
non-linear combinations of local interactions among the entities, and (c) the
rules do not depend specifically on the chemical nature of the entities."
=============================================================================

Glosses:
By "entities" I mean systems which may exist independently, and which
make up the system by simple addition to it.  Thus the protein molecules
in a crystal are entities in this sense, but the atoms in a molecule are
not "entities" composing the molecule.

By "non-linear" I simply mean the mathematical connotation, as in "non-linear
function".  I wished to use this term in the definition rather than the
less general adjective "non-additive".
===========================================================================

Now some questions and tentative answers.

1. Do such systems exist?
   
   Yes they do.  Three systems with emergent properties that have been
   well examined are (a) artificial neural networks, (b) organisms that
   exhibit schooling or flocking behaviour, and (c) cellular automata.

2. You say that the properties are independent of chemical nature of the
   entities.  Does this mean you espouse a non-mechanistic view?
   
   Not at all.  Let's take flocking behaviour as an example.  It appears
   to arise when entities have a mechanism for detecting spatial proximity
   of identical entities and a feedback mechanism for maintaining a range
   of postions relative to their neighbours.  Essentially identical
   behaviour can arise in organism as diverse as fish, insects and birds.
   It could also arise in collections of robots made out of Lego (tm) - all
   that is required is there be physical mechanisms for _instantiating_
   the local interactions.  If I were studying sandpipers, say, I would
   certainly hope to elucidate the physiological and biochemical mechanisms
   of recognition and feedback, and to learn how the relevant genes have
   evolved to optimise these interactions for efficient flocking behaviour.
   The _instantiation_ of the behaviour does depend on mechanisms which
   obey the laws of physics and chemistry, but the behaviour itself trans-
   cends these laws.

3. Aren't these rules merely empirical inventions that will be unnecessary
   when we understand the mechanisms fully?
   
   I don't think so.  The work in this area indicates many of the "rules"
   governing such properties are universal, and have a formal logical
   structure and grammar.  In the sense that thermodynamics is a formal
   system independent of any specific physical system, so are the laws
   governing emergent properties.  However, it is true that like
   thermodynamics, "emergo-dynamics" will be ultimately related to
   lower-level physical theories.

4. Aren't all properties of matter "emergent" - e.g. the properties of
   water?
   
   Not in the sense I have defined.  The properties of water depend
   absolutely on the specific interactions of water molecules, whereas
   the properties I have called "emergent" would arise no matter what
   entities are involved.

5. Simple things like flocks and cellular automata don't convince me -
   these are just computer games.  Is there any evidence that *real*
   biological behaviour can be 'explained' by such notions?
   
   I'm glad you asked.  See the amazing chapter by P. Hogeweg (cited below)
   in which he models such high-level behaviours as bumblebee sociology.
   The fact that successful models of living systems can be constructed
   out of computer instructions or Lego indicates that the properties being
   modelled are 'real' ones.

6. Wait a minute!  I'm beginning to think you are a Moravecian (see Hans
   Moravec, "Mind Children").  Do you really think biological properties
   including (choke) consciousness could arise in machines?  Is Data (in
   Star Trek) really human after all?  Do you think human beings are
   machines?
   
   Yes.  In fact, my conviction that my humanity has "emerged" from the
   properties of molecules contributes mightily to that emergent property
   of me, that I call a "religious world-view".

7. How can I learn more about such area so that I can critically discuss
   this topic on talk.origins?
   
   Start with the "Artificial Life" volumes from the Santa Fe insitute,
   published by Addison Wesley.  In my next posting, I'll re-post a
   *long* annotated bibliography that was prepared by G. Miller and P. Todd,
   and posted in sci.bio a year ago.

-----
Bibliography and Footnotes:
==========================

From the annotated bibliography, in C.G. Langton, editor, "Artificial
Life I", pp 527-625, Addison Wesley, 1989.

(a) Titles containing the word "_emergent_" or "_emergence_".
=============================================================
J.H. Holland.  "Studies of the Spontaneous Emergence of Self-Replicating
Systems using Cellular Automata and Formal Grammars."  In A. Lindenmayer
and G. Rozenberg, editors, "Automata, Languages, Development", pp 385-404,
North Holland, 1976.

J.J. Hopfield.  "Neural Networks and Physical Systems with Emergent
Collective Computational Abilities."  Proc. Nat. Acad. Sci. 79:2554-2558,
1982.

S.A. Kauffman.  "Emergent Properties in Random Complex Automata."
Physica D, 10, 1984.


(b) Titles that are germane to this posting.
============================================
C.W. Reynolds.  "Flocks, Herds and Schools: A Distributed Behavioural
Model".  Computer Graphics: Proceedings of SIGGRAPH '87, 21(4):25-34,
July 1987.

S. Wolfram, editor.  "Theory and Applications of Cellular Automata."
World Scientific, Singapore, 1986.

P. Hogeweg.  "MIRROR beyond MIRROR, Puddles of LIFE".  In C.G. Langton,
editor, "Artificial Life I", pp 297-316, Addison Wesley, 1979.



Towards a legitimisation of emergent behaviour?
===============================================
From C.G. Langton, in "Artificial Life I" page 3:
" The "key" concept in AL is _emergent behaviour_.  Natural life emerges
  out of the organized interactions of a great number of nonliving molecules,
  with no global controller responsible for the behaviour of every part.
  Rather, every part is a behav_or_ itself, and life is the behav_ior_ that
  emerges out of all the local interactions among individual behav_ors_.  It
  is this bottom-up, distributed, local determination of behaviour that AL
  employs in its primary methodological approach to the generation of
  lifelike behaviors. "

From R. Dawkins, _ibib._ page 209 (discussing the biomorphs produced by his
'Blind Watchmaker' program):
" ... Our watchword is that as much as possible must emerge rather than being
  designed.  But having seen the range of phenotypes that emerge from the
  basic program, can we think of any modifications to the basic program that
  seem likely to unleash opulent flowerings of new emergent properties? ... "

--

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: Prof. David O. Tinker      INTERNET: dtinker@blunile.guild.org        :
: Dept. of Biochemistry                uunet.ca!beltrix!blunile!dtinker :
: University of Toronto           FAX: (416)978-8548                    :
: Toronto, Ont. M5S 1A8         VOICE: (416)978-3636                    :
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