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 [log in to unmask] ---------------------------------------------------------------------- To sign-off Parkinsn send a message to: mailto:[log in to unmask] In the body of the message put: signoff parkinsn