Biology Reference
In-Depth Information
CHAPTER
2
Key Pri
nciples of Morph
ogenesis
The advancement of developmental biology depends on facts about real organisms,
acquired by painstaking experiment and careful observation. No science, however, consists
of facts alone; only when hard-won knowledge is synthesized into principles can researchers
hope to reach something that deserves to be called 'understanding'. Principles serve several
functions; they unite a body of factual knowledge into something concise enough to grasp,
they assist with the design of insightful experiments, they help to provide a framework for
the presentation and evaluation of new discoveries and, when the principles are not too
vague, they can be used to make testable predictions.
There are two broad theories about how principles arise in science. In one view, tradition-
ally associated with Francis Bacon but more fairly attributable to a combination of William of
Ockham and John Stuart Mill,
1
experiments come first and principles emerge later from
consideration of their results. In the other view, traditionally associated with Karl Popper,
hypotheses about principles come first and the role of experiments is to attempt to disprove
them.
2,3
Biology operates in both Baconian and Popperian modes
4
and can switch between
the two many times even during the course of a single project. It is common, for example,
for the phenotype of a random mutant to suggest a new idea in the Baconian manner, and
then for that idea to be tested by experiment in the Popperian manner. This dual mode of
thinking, used by almost all biologists whether they are explicitly aware of it or not, poses
a dilemma for the author of a textbook: should the presentation of a conceptual framework
follow the presentation of experimental data, or
vice-versa
? Discussing concepts only after the
data have been presented would enable a reader to assess their meaning with an unbiased
mind rather than through the filter of principles that may turn out to be fallacious. Experi-
mental results are, however, much easier to present and to read in the context of a conceptual
framework, if only because such a framework can help to explain why there is a point to
discussing a particular experiment in the first place. This topic therefore attempts a compro-
mise between the two strategies. This chapter and the next will set out some key concepts of
morphogenesis in the broadest terms because these concepts set the agenda for, and are used
many times by, the chapters that constitute the experimental core of the topic. Chapter 28, at
the end of the topic, will then discuss the principles in more detail, in light of the data that
will by then have been described.
The key concepts that are introduced briefly in this chapter are the idea of a 'mechanism',
the principle of emergence, the use of feedback, and the differences between self-assembly
and adaptive self-organization.
