February 12, 2004
Ted Wong
Why Evolution by Natural Selection Isn't Emergent
(this outline first appeared at http://emergent.brynmawr.edu/eprg/?page=WhyEvolutionByNaturalSelectionIsntEmergent)
Many people think evolution by natural selection
is emergent.
There is no designer.
Enormous complexity came out of iterations of simple rule(s).
This complexity includes well defined levels of organization.
Organisms interact with each other, both directly and through
interactions with the shared environment.
Unpredictable outcome: Gould's tape would replay differently.
But (just to be clear) what is the emergent phenomenon? I can
think of a few possibilities:
The emergent phenomenon is diversity. Here you have
to think of the growth of the Tree of Life, and the fractal-like
form of the tree emerges from all the various lineages bifurcating
off of one another.
The emergent phenomenon is cognition. Or it's photosynthesis or
some other amazingly complicated feature of some organisms.
The emergent phenomenon is organization, and the agents can be
anything in the "lower" levels: atoms, molecules, macromolecules,
cells.
Is biodiversity emergent?
I press dough into a mold. The dough takes on the
shape of the inside of the mold. Putatively emergent phenomenon:
global shape of the dough.
Yes: dough molecules interact with themselves and with the mold.
Global dough shape is the sum of the molecule positions, but the
molecules weren't placed in position by a designer.
No: the dough's final shape was merely transferred from the (designed)
mold to the dough. The shape didn't arise in the dough molecules;
in fact it constrained the interactions available to the molecules.
You can tell the direction of pattern transfer because the final
dough shape is predictable from the mold shape.
An earthquake knocks dough off a shelf into a coconut shell. The
dough takes on the shape of the inside of the shell. Putatively
emergent phenomenon: global shape of the dough.
Yes: neither the pressing of the dough into the shell nor the
shape of the shell was intended by a designer.
No: again, the global shape of the dough didn't arise from interactions
among the dough's component molecules. There was still a designer:
the shell.
An earthquake knocks dough off a shelf into a balloon. The balloon
fills with dough and assumes its full-inflation shape. The dough
takes on the shape of the inside of the balloon. Putatively emergent
phenomenon: global shape of the dough.
Yes: the global shape of the dough was a collaboration between
the dough and the balloon.
No: it's not real collaboration, because the balloon's final shape
is determined by the distribution of latex density (or something
like that), which was itself designed by a balloon engineer.
A bunch of helium-filled balloons are released into Schwartz Gymnasium.
Balloons accumulate in the high points of the ceiling. Putatively
emergent phenomenon: the distribution of balloons.
Yes:
No: again, you know where the high points are, so you know where
the balloons will go. Here there isn't even the question of interactions
among balloons.
A growing population of organisms spreads by diffusion across
a phenotype space. Because of selection, organisms tend toward
fitness peaks. Putative emergent phenomenon: biodiversity.
Yes:
No:
Is complicated adaptation X emergent?
If peak X in a phenotype space is occupied, is that
peak (or its occupation) emergent?
In a diffusion process, is the position of some particle ever
emergent?
Is organization emergent?
Sure.
How is emergence important in the study of evolution?
Development is emergent. A butterfly's camouflage
pattern is ultimately the result of selection by predators and
bark patterns (which together make a sort of designer). It proximately
results from local interactions among cells and morphogens. That's
where emergence comes in, and that's what's fascinating about
the evolution of development. Selection acts on the agents by
selecting global behaviors.
Additions, revisions, extensions are encouraged in the Forum
and/or at emergent.brynmawr.edu
Participants for October 28, 2003: Ted Wong, Paul Grobstein,
Jim Marshall, Doug Blank, Karen Greif,
Al Albano, Anne Dalke, Mark Kuperberg, Alan Baker, Tim Burke,
Hannah Wilhelm, Jim Wright (12)
