Posted by GaDS on August 28, 1998 at 20:09:24:
In Reply to: More posted by Carlos on August 28, 1998 at 18:58:54:
: GaDS said:
: "As regards my query "Why haven't scientists in labs been able to duplicate in labs what supposedly occurs in nature" I was referring to the creation of life from non-life.
: As rpcman said, the question of abiogenesis is different than, and separate from, that of evolution...
Ah, yes, but you must realize that if one takes the view that Nature, not a Creator, is responsible for the life now on Earth, that abiogenesis must be the prelude to evolution. I have met very few who believe that a Creator began the process, and then let the kettle boil on its own. (NB: This relates to one of your questions regarding theories, RPCman.)
: You are right, no life has been created. Nature, however, had hundreds of millions of years to accomplish it, and scientists have only been experimenting for a few decades.
True enough, but as I pointed out in a previous post the millions of years were only necesssary to build the necessary components up to the right concentrations and proportions. At some point, at some specific moment, non-living matter would have become living matter, just as a paper may smolder and then suddenly ignite into flame. Abiogenesis infers that scientists should be able to assemble all the constituent parts of a cell, put them together, and have them come alive. I have yet to hear of anyone succeeding at this.
: Some progress has been made. I'm sure you've heard of the experiment (I can't recall who did it) where amino acids were formed by putting an electrical current through a "soup" of chemicals.
I believe the scientist you are referring was someone named Miller. I do recall the experiment, but it's a far cry from synthesizing some small amino acids and having them assemble spontaneously into structural proteins, enzymes, nucleic acids, much less organize into the cellular structures of ribosomes, mitochondria, endoplasmic reticula, cell membranes, and so forth. By chance alone one can toss a cork and bottle into the air and have the bottle land upright with the cork in the bottle. It's another thing to toss all the components of a BMW into the air and have it come down a fully assembled and functioning automobile.
: Also, I recall reading that a certain virus (the tobacco mosaic?) spontaneously assembles itself if its constituent chemicals are combined.
As far as I know, the debate still goes on as to whether viruses are alive or not. Viruses are essentially strands of nucleic acid that hijack the mechanism of a cell to replicate, and by implication are most likely a de-evolution of cells rather than a predecessor. Why is this implied? Because if the viruses require more complicated organisms to replicate, and replication is necessary for then until those organisms are present they can't do anything. If so, they can't be the ones that are the progenitors of the more complex organisms they use.
: No matter how one chooses to consider it Nature at some point was supposedly capable of genetically isolating progeny of a common ancestor.
: One mechanism that can and has been observed is a change in karyotype - the number of chromosomes. I quote from the Talk Origins archive:
: "There are many different ways that the karyotype can change. The most drastic is polyploidy, where the entire genomic complement gets duplicated two or more times. Within that, there is allopolyploidy, which happens in crosses between organisms of different karyotype, and autopolyploidy, which happens in crosses within the species. Wait a minute, you might say, didn't I just get through saying that different karyotypes were usually a bar to reproduction? Yes, the "usually" does not include allopolyploidy. Other means of changing karyotype include fusion, the merging of two or more chromosomes into one; fission, where one chromosome is divided into two chromosomes; and replication of particular chromosomes. (Trisomy-21 is the name for the retention of an extra copy of the 21st human chromosome, which causes "Down's Syndrome."
I am aware of these mechanisms and the fact that they occur. For these to have any affect on the population they must occur in the germ cells, rather than somatic cells, so that they will be passed on to succeeding generations. As was touched upon, these typically result in abnormal development, sterility, or other complications. In some cases they do not, but that leads to the following: IF one of these chromosomal anomalies occurs and IF it is passed on in a gamete and IF it is not fatal and IF it produces a measurable difference in phenotype and IF that conveys some discernible advantage to survival and IF it is compatible with the gametes of a normal individual (or that mutant mates with an individual with a similar chromosomal anomaly) and IF the change does not interfere with mating (either selection of a mate and mating itself) and IF the change is dominant THEN that phenotypic change will appear in the next generation. That's a long way from speciation, because it would have to happen over and over and over again unless other mechanisms were available that would result in a similar change in phenotype. Suppose, for example, it resulted in a finch having a beak 1/2" longer than normal so that it could forage for insects hiding in deeper cracks than most. Would an identical change in chromosomes somewhere down the road result in an even longer bill? Probably not, as the change probably resulted in a bill x + 1/2" rather than an additional 1/2" to whatever it would have been. A separate question raised by the fusing or splitting of chromosomes is that since each partner contributes have a chromosome to the zygote, why are most if not all populations found with pairs of identical chromosomes rather than individual chromosomes of varying construction? For instance, suppose a chromosome set changed from VV VV II II to VV YY II because some mechanism fused a VV and II set together to make a YY set. When the individual mates with a normal individual, it contributes X Y I and the normal individual contributes X X I I. The resulting zygote would then have XX Y I II because the Y has nothing to pair with and neither does the I. If chromosome split, the same thing would occur except you would have 3 unmatched sets. If this really is a major mechanism leading to speciation, why do most if not all species have paired chromosomes (other than perhaps the sex chromosomes like the X and Y pair in human males)?
GaDS
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