Biology Reference
In-Depth Information
FIGURE 25.1 Wilhelm His' 1874 illustration of the similarities between the side-lobes made by a rubber tube
forced to bend sharply by the tense hook illustrated, and the optic lobes pushing out from the neural tube of a chick
embryo. 3
emerge as sideways bulges from the chick neural tube. In his resulting publication, 3 he noted
that if a simple rubber tube is forced to bend sharply, it develops lobes very similar to the
optic lobes, and speculated that the optic lobes may therefore be the result of such bending
( Figure 25.1 ). In an age dominated by vitalism, this suggestion marked an important change
of emphasis towards understanding the embryo through ordinary physics.
One of the most famous researchers to work this way was the Scottish naturalist and clas-
sicist, D'Arcy Thompson. In his 1917 topic On Growth and Form, 4 he pointed out how strongly
some organisms resemble physical objects. Jellyfish medusae, for example, were compared to
the transitory fringed splash craters formed when one drop of milk falls into a bowl of the
same liquid. Similarly, the outlines of cells in a tissue were compared to the polyhedral
shapes of bubbles in soap foams. In those early years, too little was known about the real
morphogenetic systems of cells (for example, the cytoskeleton and cell-cell junctions) for
this type of physical modelling to engage directly with mechanistic cause-and-effect. Later
physical models, such as the rod-and-elastic model for invagination described in Chapter
26, were based on the function of identified sub-cellular systems and were therefore much
more useful in testing whether tissue-level behaviour could emerge from the coordinated
actions of particular sub-cellular mechanisms.
Mathematical modelling of morphogenesis had some precedents before the age of widely
available computing power, 4,5 but it has become much more common in recent decades. It
has the advantages that it is usually quicker to write a computer model than to construct
a physical one and parameters such as size and stiffness can change dynamically in
a computer simulation in a way that cannot be accommodated physically. )
) It has become common in recent years to refer to computer models as 'in silico', a phrase dating back to
a paper published in 1991. 6 The phrase involves such a serious error of Latin declension that its use is best
avoided.
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