Murray,

Kudos to Stephen Jay Gould for defending ours point of view in a most elegant ,
scientific and brilliant form ....  :)

Murray Kastner wrote:

> AUG 27, 2001
>
> What Only the Embryo Knows
> By STEPHEN JAY GOULD
> homas Henry Huxley designated three men as the finest intellects of
> 19th century natural history: his dear friend Charles Darwin; his
> most worthy opponent Georges Cuvier; and Karl Ernst von Baer, who
> discovered the mammalian egg cell in 1827 and wrote the founding
> treatise of modern embryology in 1828. Of these three, posterity has
> largely forgotten von Baer, who suffered a severe mental breakdown in
> the 1830's, but then recovered and moved to Russia (not uncommon for
> a German-speaking Estonian national), where he enjoyed a
> distinguished second university career, largely in anthropology and
> lasting well into the 1870's.
>
> In 1828, von Baer enunciated the central principle of embryological
> development, later known as "von Baer's law" and now regarded as the
> correct interpretation of Ernst Haeckel's famous (and erroneous)
> claim that "ontogeny recapitulates phylogeny," or that the successive
> forms of embryology repeat the adult stages of a lineage's evolution
> - with the gill slits of an early human embryo representing an
> ancestral fish and the later tail an ancestral reptile, for example.
>
> By contrast, von Baer proposed a principle of progressive
> specification and differentiation: One can first tell that an embryo
> will become a vertebrate and not some sort of invertebrate, then a
> mammal and not another kind of vertebrate, then a carnivore and not a
> rodent or ruminant, then a dog and not a cat, and finally Buster the
> Beagle and not another breed.
>
> Von Baer summarized his principle in an epigram: "The development of
> the organism is the history of growing individuality in every
> respect." In other words, successive narrowing and determination of
> parts as complexity coagulates. No turning back after the blueprint
> becomes finalized from a broad mass of initial potential. For an
> appropriate literary metaphor, think of Lot's wife or Omar Khayyam's
> lines: "The moving finger writes; and having writ, moves on."
>
> Von Baer's law epitomizes the central issue, unfortunately rarely
> discussed and little understood, in our current debate over embryonic
> stem cells. The very structure of material reality imposes a
> principle of trade- offs in both nature and human affairs: One always
> gives something in order to gain. In particular, we usually pay for
> complexity by surrendering flexibility - and von Baer's law
> encapsulates the embryological version of this structural generality.
>
> In genetic terms that von Baer could not know, each cell of our body
> contains a full set of genes. But embryological differentiation into
> a specialized adult role - as a brain cell, liver cell or heart cell,
> for example - leads to a "freezing" or "turning off" of most of this
> potential apparatus, leaving active only those few components
> regulating the specialized adult form and function. The cells of the
> earliest, undifferentiated embryo (little more than a clump of
> identical units in appearance) maintain full capacity to develop in
> any direction; that is, all their genes remain potentially active and
> recruitable.
>
> The irony of the trade-off, explicitly recognized by von Baer nearly
> 200 years ago, inheres in the evolved surrender of this embryonic
> flexibility as development proceeds toward our maximal complexity.
> Cut a planarian flatworm in two, and the tail end regenerates a head
> while the head end regrows a tail. For in this simplest of
> bilaterally symmetrical invertebrates, with minimal differentiation
> of internal organs, all cells retain the embryonic potential to build
> any part of the body. This capacity for regeneration - the ability of
> cells at a wound site to "dedifferentiate," or return to a state of
> early embryonic flexibility - becomes progressively lost in animals
> that evolve greater adult complexity by von Baer's universal process
> of "locking in," with increasing specialization of parts. We have, in
> short, traded regenerative capacity for the undeniable evolutionary
> advantages of maximal complexity.
>
> For this reason, we must use embryonic stem cells if we wish to
> pursue a large body of enormously important, highly promising and
> deeply humane research in how specific tissues and organs grow from
> the broad potential of early cells derived from the fertilized ovum.
> Speaking personally, I do not grant the status of a human life to a
> clump of cells in a dish, produced by fertilization in vitro and
> explicitly destined for discard by the free decision of the man and
> woman who contributed the components. But I also have no desire to
> offend the sensibilities of those who disagree. Thus, if I could
> derive cells of similar flexibility in a different way, I would
> gladly do so, even at considerable extra time and expense. (By
> analogy, I did not mean to mock or flout our laws in using marijuana
> to stave off severe and continuous nausea during some particularly
> nasty and lengthy chemotherapy 20 years ago. But I tried all the
> available anti- emetics, and they just didn't work. I continue to
> regard my decision as fair, humane and, believe me, importantly
> sustaining and life-affirming.)
>
> Unfortunately, von Baer's law, and nature's broader structural rules
> of trade-off between complexity and flexibility, give us no
> alternative to embryonic stem cells for now - and the research is
> important and far more than merely theoretically lifesaving.
> (Moreover, if we hope to find ways to dedifferentiate adult cells -
> and therefore learn to recover the requisite flexibility from cells
> derived without offense to anyone - then we must experiment with
> embryonic cells in order to understand and control the mechanism of
> their broad potentiality).
>
> As an old man, from his Russian periphery, von Baer made the famous
> and rueful remark that all new and truly important ideas must pass
> through three stages: first dismissed as nonsense, then rejected as
> against religion, and finally acknowledged as true, with the proviso
> from initial opponents that they knew it all along. Genetic
> technology has brought us through the first stage. Our current debate
> on stem cells resides in von Baer's second stage, with the religious
> views of a clear, if powerful, minority setting an unfortunate
> opposition to one of the most vital avenues of beneficial research in
> our time. The third stage will arrive, and we will marvel that we
> ever rejected a pathway toward knowledge so imbued with life-saving
> capacity. May this third stage come soon, as our understanding
> differentiates further into a true and humane grasp of the virtues of
> flexibility.
> Stephen Jay Gould, a professor of zoology at Harvard, is the author
> of ``Questioning the Millennium.''
> Copyright 2001 The New York Times Company

Cheers,
Joao Paulo - Salvador,BA,Brazil
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