On Sat, Feb 05, 2005 at 12:07:59AM -0800, DJA wrote: > Lan Barnes wrote: > >On Thu, Feb 03, 2005 at 11:46:03PM -0800, DJA wrote: > > > >>Remember, in many cases, a birth defect is nature's attempt to adapt to > >>a changing environment. It usually takes many, many failures before the > >>adaptation is successful. That's just basic biology. Attempting to > >>prevent all genetic "defects" is tantamount to taking away nature's > >>ability to learn from its mistakes. Not only can we *not* prevent all > >>birth defects, we should *not* do so. > > A program of gene manipulation could well treat lack of diversity as a sort of defect. ... > >The greatest birth defect is a miscarriage (or it's egg equivalent), and > >as much as they've been selected against (anyone on this list have a > >miscarriage as an ancestor? Thought not), they still happen with a > >fairly high frequency. > > Again Biology 101. A miscarriage is not a birth defect but rather a > response to a catastrophic birth defect which would otherwise lead to > the probable non-viability of the the fetus.
I'm wondering if this definition is too narrow and too oriented around easily observed miscarriages. It seems reasonable to conjecture (perhaps it has even been observed) that many mutations cause production of a vital protein to be completely replaced by production of a useless modification. The embryo will die as soon as the protein is needed or at least as soon as any pre-existing stock of the protein becomes insufficient. Unless the protein has a sufficiently subtle function to behave very differently in a small embryo than in a much larger organism, the embryo will die very early. I'm guessing that three particularly dangerous times are right after fertilization, during the first cell division, and when the total rate of energy consumption of the embryo becomes significantly larger than that of the egg. Unless the mother's body detects the problem very rapidly, the miscarriage will be a response to a stone-dead embryo, smaller than a pinhead, rather than a living but probably eventually non-viable one. I'm not sure the former kind of miscarriage is usually recognized at all. Stewart Strait -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
