Biology Reference
In-Depth Information
CHAPTER
25
Modelling Morphogenesis:
A Brief Overview
The first edition of this topic contained no separate section on modelling morphogenesis,
and such an addition may still be seen as out of place in a book that focuses on biological
mechanisms themselves rather than on how they are studied. Nevertheless, there are good
reasons for covering some aspects of modelling explicitly, in addition to citing the results
of modelling studies in some of the foregoing chapters. One reason is that modelling is
becoming increasingly common in all areas of biology, but its strengths, weaknesses and
purpose are still frequently misunderstood. Another is that as mechanistic understanding
of morphogenesis matures, it should be subjected to rigorous testing; some tests are best
done through modelling, particularly modelling in vivo using synthetic biology.
To begin with a definition: a model is a representation of the interesting parts of a system
that omits the system's other, irrelevant, features. Some omitted features are irrelevant
because they really have nothing to do with the phenomenon under study, while others
may be considered unnecessarily detailed and are represented instead by simple abstract
higher-level behavioural rules. To take a human-scale example, traffic planners modelling
the flow of vehicles along a planned road intersection will completely omit features such
as trees that exist only in the spaces between the roads because they have nothing to do
with traffic flow. They will also omit the details of pistons and cam shafts and gears within
each car because there is no need to consider them in detail: it is sufficient instead to represent
each vehicle as an object that obeys a set of high-level behavioural rules about changing
velocity in response to vehicles nearby (with a certain element of randomness). The whole
point is that, by discarding detail that is too fine to matter, a system can be simplified so
that what does matter can shine through.
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Deciding what details can be safely omitted calls
for skilled judgement: as Einstein remarked, everything should be as simple as it can be, but not
simpler.
)
The idea of modelling aspects of morphogenesis using physical, mathematical or biolog-
ical systems has a long history. In 1873
e
1874, Wilhelm His, the discoverer of the neural crest
and the inventor of the microtome, was studying the development of the optic lobes that
)
This remark of Einstein was first quoted by the composer Roger Sessions (who knew Einstein) in the article
'How a “difficult” composer gets that way'.
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