Biology Reference
In-Depth Information
with irreducible properties that he explains more precisely using the
field concept.
30
Like particles which conform to the magnetic field in
which they are placed, each individual cell of an embryo, or tissue,
must conform to the morphogenetic field to which it belongs.
“
Let us take a circumscribed body, depending for its maintenance
on active exchange with its environment; for instance, an egg in a
pond, a cell in a tissue, a human individual in a society. Then let
the unit multiply into a few more units; they all continue to have
a share in the common interface of exchange and communication
with the medium. But let the number of units keep on increasing,
whether by subdivision or accretion, and all of a sudden a critical
stage arises at which some of the units find themselves abruptly
crowded inward, cut off completely from direct contact with their
former vital environment by an outer layer of their fellows.
The latter thereby acquire positions not only geometrically, but
functionally mediatory, between the ambient medium and the
now inner units. From then on, 'inner' and 'outer' units are no
longer alike. A monotonic group of equals has become dichotomised
into unequal sets. With the emergence of the distinction between
innerness and outerness, the
1
+
1
=
2
rule becomes inapplicable
”
(SL pp. 31-32).
The morphogenetic field corresponds to this external/internal
polarity which is propagated within a population of cells and causes
their differentiation. Indeed:
“
Interactions between the 'outer' members and their newly estab-
lished inner' neighbors would expose to another set of new condi-
tions any fresh units arising subsequently in the intermediate zone
between them, and hence call forth in them a third type of reaction.
Moreover, polarised influences from outside would impose an axiate
pattern upon the group. Thus would ensue a train of sequelae of
30
Since Weiss, the idea of the morphogenetic field has been widely used in
embryology.
