new evo devo love affair & origins of mydi~ideas?!

The love affair
between development and evolution
has not always been easy.

The emergence
of causal embryology in the late 19th century
triggered developmental biologists to focus on their favoorite animal
or piece thereof
[at the expense of a wider consideration
of animal forms],
whereas evolotionists have understandably
shown little interest in the complex mechanisms
underlying variations.

The passion
in this old couple was nevertheless revived in the early 1980s,
following several revolutionary discoveries
that led to the novel discipline
of "evo-devo."

Endless Forms Most Beautiful,
as the subtitle of our present myDiBook indicates,
is about this 'new science,'
a qualification somewhat at odds
with a major concept the author Sean Carroll develops in his book:
that NOVEL FORMS
ARE ALWAYS MODIFICATIONS
OF PRE-EXISTING ONES.

THIS
LIKELY ALSO APPLIES
TO THE HISTORY OF IDEAS
AND DISCIPLINES.

It is admittedly difficult
for todays's young biologists
to imagine the impact of these discoveries
on our conceptual frameworks,
and we wonder how people possibly
have thought differently
before.

SC
[a developmental geneticist]
takes us for a journey into the early days of the field,
introducing the fundamentals of evo-devo
through historical
perspective.

THIS
is not always the simplest way
to give a state-of-the-art account
of a particular field
of research,

YET
the author
succeeds in
this task.

The book opens
with a clear introduction
of both the context and the basic tenets
of evo-devo.

SC explains
the relevance of developmental machanisms
as sources of evolutionary
innovation.

He presents
evo-devo as a science of inference,
in which molecular features such as gene expression
or regulatory specificities observed in two distinct animals
are postulated to have existed
in their common
ancestry.

THIS
really is
THE modus operandi
of the discipline,
and throughout the book
he offers many illuminating examples
to validate this
approach.

So
WHAT was the
EVO-DEVO revolution
ABOUT?

We can
recognize
several key
claims.

First,
GENES
CONTROL
DEVELOPMENT.

Second,
ALL ANIMALS
DEVELOP BY USING
THE SAME SET
OF GENES.

Third,
THE BASIC
GENETIC PRINCIPLES
UNDERLYING ANIMAL DEVELOPMENT
ARE SHARED.

That is,
the same genes
are used in much the same way,
and they participate
in the same networks,
which in turn interact with each other
in a rather generic fashion
throughout the animal
kingdom.

Last,
various parts
of the same animal
are built following
the same logic,
again by using similar modules
and networks
of genes.

Nature
is parsimonious,
and things that work
in particular functions
are often subsequently recruited
in parallel with the emergence
of evolutionary
innovations.

Tinkering,
multifunctionality,
redundancy,
and modularity are THE key words of the discipline;
also crucial is the notion of a genetic "tool kit" for animal development,
a notion that is used throughout
the text.

As
one would expect,
arthropods occupy a large share of the description,
which reflects BOTH the history of the field
AND the expertise
of the author.

SC
discusses the impact
of sequencing the entire DNA of species,
which has revealed great similarities among genomes of different species,
and the concurrent change in paradigm that leaves us wondering
why then are WE so different
from OTHER
animals?

The
chapter
dealing with primate evolution
[subtitled "The Making of Homo sapiens"]
is especially thought-provoking
in this respect.

Among
the various tool kits,
the Hox gene family receives special attention because of its importance
in the development of these
new concepts.

Yet
no explanation,
not evena tentative one,
is offered as to WHY THIS group of genes had [have]
such a high epistemic
value.

SC shows
how modifications in Hox gene regulation are associated with changes in forms -
how minor causes can lead to major morphological effects
such as the presence or absence
of legs and wings.

Nonetheless,
among the various examples SC provides to illustrate this basic principle,
I most enjoyed the chapters dealing with phenomena where these latter genes have little
if any importance: the questions of butterfly eyespots, mammalian coat colors,
and mimicry.

THESE
are discussed at some length,
but anyone interested in knowing how butterflies can display such a variety of splendid wings
will enjoy the
details.

EVO-DEVO
bears great hopes,
but the approach also carries significant drawbacks.
THIS is one aspect of the field that
may have deserved
more attention
in this book:
SC indeed tells us the BEST of evo-devo,
discussing case studies in which developmental genetics, often backed up by functional assays, is associated with BOTH molecular biology AND a good knowledge of systematics
and evolution.

Not
ALL studies
are SO comprehensive,
and overly bold hypotheses are not rare in the field.
At times, researchers take the "one P-one T" approach
[one polymerase chain reaction to one theory],
through which a mere expression domain
can generate grandiose
theories ...