Biology Reference
In-Depth Information
organism founded on mechanisms that are not amenable to rapid evolution cannot evolve
quickly. Consider a hypothetical primitive organism, the development of which involves
only very few morphogenetic events. Modification of the developmental programme so
that an existing morphogenetic event is replaced with a new one would probably be rela-
tively straightforward; perhaps the mutation of a single protein would be enough to turn
a convex curvature into a concave one, for example. Modification of the developmental pro-
gramme so that a new event is added, without removing an existing event would, however,
be more or less difficult depending on how it was done. If it were done by the activation at an
additional time and place of a morphogenetic mechanism (integron) that already existed
somewhere else in the developmental programme of the organism, then the modification
may be relatively straightforward. If, however, it had to be done by the evolution of a brand
new mechanism, it would probably be much less likely to occur in a reasonable length of
time. For this reason, evolution of new morphogenetic events by invoking existing morpho-
genetic mechanisms at new times and places, and in new combinations, is more likely than
the creation of new mechanisms
de novo.
Sharing of low-level integrons by different high-
level ones would therefore be expected to be a feature of phyla that have played the evolution
game successfully. This does not, however, preclude some
de novo
invention and, as
explained in the section on modularity above, there is evidence for 'new' proteins having
been added to modify the function of low-level integrons in certain times and placed in
the embryo. Mutation and selection just happen; they are not constrained to respect the
boundaries scientists draw between processes.
LOO
KING FORWARDS: WHAT REMAINS TO BE DO
NE?
I have written many times in this topic that our understanding of the mechanisms of
morphogenesis remains at a fairly primitive level, despite the quite brilliant work that has
been done by imaginative researchers in the field. Although the great questions of the field
are at least 2000 years old, researchers have had good enough tools to make a serious attempt
at answering them for fewer than 20 years. For this reason, the field still feels young and it has
only recently become fashionable.
)
Where might it be heading, and what remains to be done
before morphogenesis is properly understood?
Without wanting to delve too deeply into epistemology, the answer to that question
depends very much on what is meant by 'understanding'. Each science has, at a particular
time, a consensus on what constitutes an understanding. For a physicist, something may
be considered to be 'understood' if it can be expressed in a mathematical equation. For an
organic chemist, understanding a reaction may mean being able to express it as an equation
)
In writing this topic, I have been struck by how many important and perceptive papers (that advance
the field of morphogenesis considerably) are published in journals with low-impact factors. Either the
field of morphogenesis has a gratifyingly high proportion of researchers who pay no attention to the
currently fashionable but nonsensical idea that publishing in certain journals is somehow intrinsically
better than publishing in others, or it has been very hard for them to have their excellent work taken
seriously by journals that concentrate on publishing only work likely to be cited many times soon after
publication.
