Biology Reference
In-Depth Information
S'
D'
X'
F'
Fig. 15.4 An
external
(or exo) view of the “dissipative structure theory of morphogenesis”
(DSTM). S
0
¼
synthesis of X
0
in extracellular space (ECS). D
0
¼
destruction of X
0
in ECS.
F
0
¼
Extracellular functions, including the construction and destruction of extracellular matrix,
the production and control of pericellular ion, metabolite, and intercellular messenger gradients. X
0
includes extracellular matrix proteins, and S
0
includes exocytosis of precursor proteins of X
0
, and
D
0
includes the various matrix metalloproteinases. In contrast, Fig.
15.2
can be viewed as an
internal (or endo) view
of the “dissipative structure theory of morphogenesis”
15.6 The Tree-Ring-and-Landscape (TRAL) Model
of Evolutionary and Developmental (EvoDevo) Biology
Dendrochronology,
the science of tree-ring dating, uses tree rings as a means to
determine not only the age of trees but also to reconstruct the climate changes, since
climate affects the tree growth and tree rings thus serve as a historical record of
climate changes. The American astronomer A. E. Douglass (1867-1962) originally
developed this technique in the first half of the twentieth century in order to
understand cycles of sunspot activity. He reasoned that changes in solar activity
would influence climate patterns on the earth which would in turn affect tree-ring
growth patterns. In other words, Douglass correctly inferred the sequence of events
shown in Fig.
15.5
.
The main purpose of dendrochronology as developed by Douglass was to infer
the sunspot activities from the tree-ring growth patterns. The purpose of morpho-
genetic research in biology is to understand how DNA and environmental changes
bring about the shape changes in organisms within their lifetimes, that is, to
understand the molecular mechanisms by which DNA and environment interact
to bring about morphogenesis (Fig.
15.6
).
Figures
15.5
and
15.6
have more common features than may appear on the
surface. First, the tree ring is a relatively simple example of morphology. Second,
sunspot activities and the associated climate changes constitute a part of the
environment of organisms. Third, although not explicitly indicated in Fig.
15.5
,
tree rings are affected not only by sunspot activities and associated climate changes
but also by the genome (i.e., DNA) of trees because different species of trees
produce different tree-ring patterns even under identical environmental conditions.
Therefore, Fig.
15.6
is a more comprehensive representation of the causal relations
underlying morphogenesis and hence subsumes Fig.
15.5
and
dendrochronology.
It is interesting to note that the causal scheme shown in Fig.
15.6
can be
applied to either
developmental biology
or
evolutionary biology
, depending on
the timescales adopted. On the time scale of individual organism's life span
