Biology Reference
In-Depth Information
CHAPTER
1
Introduction: The Aims
and Structure of This Topic
This topic is about the shapes of living tissues and bodies. More specifically, it is about how
these shapes are created as organisms develop from simple fertilized eggs into complex
animals and plants. The creation of shape is usually called 'morphogenesis'. )
The processes that are responsible for the development of animals and plants can be
divided, for convenience, into three main categories: communication, differentiation and
morphogenesis.
Morphogenesis is the only one of these activities that is obvious to even a casual observer
of embryos and was therefore the first to be studied. Indeed, the study of morphogenesis is
one of the oldest of all the sciences, dating back to ancient Greece where Aristotle (384 e 323
BCE) described its broad features in birds, fish and cephalopods. Even at this early stage of
scientific thinking, he understood that an egg had the 'potential' for the animal's final form
but that it did not contain a miniature version of the adult. 2 Since those days, the deepest
questions of animal and plant development have continued to concern the creation of shape
and form. Until very recently, however, the molecular revolution in biology has almost
ignored this most fundamental aspect and has instead concentrated on differentiation and
communication.
It is easy to understand why. The immunologist and philosopher Peter Medawar once
defined science as 'the art of the soluble', 3 and later wrote an entertaining series of essays under
that title. This series pointed out the futility of researchers devoting their lives to tackling,
head-on, problems that were simply too difficult to solve by brute force when an intelli-
gently-thought-out series of studies on related but soluble problems might provide an alter-
native line of attack on the original issue. 4 The morphogenesis of a tissue is a formidably
difficult problem, being four-dimensional (three space, one time) and involving the inter-
action of thousands of different molecules. This makes it much more complicated to study
at a mechanistic level than either differentiation or communication. Differentiation can be
) From the Greek roots morph, meaning 'form', and genesis, meaning 'creation'. As Waddington explained
almost half a century ago, 1 'The word “morphogenesis” is often used in a broad sense to refer to many
aspects of development, but when used strictly it should mean the moulding of cells and tissues into definite
shapes'. This topic uses the term strictly.
 
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