Biology Reference
In-Depth Information
CHAPTER
28
Concl
usions and Perspe
ctives
The introductory section of this topic (specifically Chapter 2) argued that a field of research
does not become a mature science unless it has a theoretical framework that can be used to
organize and to explain empirically derived facts. After sketching out a few key concepts that
were needed for discussion of the experimental data in the core of this topic, that chapter
made the promise that the issue of principles would be revisited. This seems a sensible point
to look back over what has been presented in an attempt to draw provisional conclusions
from it and to look forwards to what remains to be discovered.
PROVISIONAL CONCLUSIONS FROM THE MECHANISMS
DESCRIBED IN FOREGOING CHAPTERS
Emergence as a Link Between the Molecular-Biological and Systems-Biological
Viewpoints
One of the key principles introduced in Chapter 2 was that of emergence
d
the way in
which systems that involve only simple interactions can give rise to complex behaviour. In
Chapter 2, this principle was illustrated with the 'Game of Life', because no real morpho-
genetic mechanisms had been described in detail by that stage of the topic.
Hopefully, the real embryonic morphogenetic mechanisms that have been described,
particularly those that could be described in molecular detail, have provided convincing bio-
logical examples of the principles of emergence. The simple interactions that govern micro-
filament polymerization and stability, for example, can 'know' nothing of the disposition of
cell-cell junctions, yet the system of interacting molecules succeeds in assembling a cytoskel-
eton perfectly adapted for generating and withstanding tensions in tissues (Chapter 5). The
local processes that regulate the assembly of a leading edge cytoskeleton can 'know' nothing
of the large-scale migration pathways set down in the embryo, yet the feedback loops
inherent in these processes ensure that the leading edge is assembled in such a way that it
automatically follows these pathways (Chapter 11). This point is made especially clearly
when migratory cells from one species (for example, mouse of quail) are grafted into another
(for example, chick) and migrate appropriately for the differently shaped body of their host
species.
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e
3
They could not do this if they were behaving according to an internal 'map' of
what shape the body should be. In one spectacular example of this type of experiment, mouse
neural crest cells were grafted into a chick host: not only did they migrate properly but,
