lonetto@phri.UUCP (Michael Lonetto) (04/19/85)
> < I am an island > > > So often I have read words to the effect: > "All you have is some fossils, and carbon radiometric dating ... ". > Surprisingly, these comments typically receive very few rebuttals. > In my last article, I mentioned the substantial independent > biochemical evidence supporting evolution. > This evidence is ubiquitous, and simple reproducible experiments > repeatedly verify its existence. Sorry about that, I was trying to quit for a while halfway through but I ended up posting an article without an end. To continue: In the Drosophilae, and in every other species so far studied (>20) there exist pieces of DNA which at this point appear to be on their own. In Drosophila these are known by a variety of technical terms such as "Multiple copy interspersed repetetive elements." All that this means is that in each "genome"(copy of the genetic information of the organism, ie a set of chromosomes), there are several copies of each of these "elements"(independant genes). Some of these elements behave much like the "transposons" (mobile independant drug resistance genes) which are found in bacteria, and have been well studied. They also show some similarity in both structure and behavior with mammalian retroviruses. The way that transposons work is that most of the time they stay wherever they are. When circumstances change they wreak havok with the genome they are occupying. In the case of the Drosophilid "jumping genes" they tend to stay put as long as there are the right number aroun and they don't end up alone. To explain: whithin any given strain OF THE SAME SPECIES there may be variation in both the types of jumping genes and the number of each type present in the genome. By strain here we can mean either an inbred laboratory strain or a geographically isolated population. As long as this strain mates with its own kind the jumping genes stay in place. BUT: If a MALE carrying say a P type jumping gene is mated to a FEMALE from somewhere else where they don't have these, then the type P elements "mobilize" and jump all over the genome. Amongst the places where they "jump" in are genes necessary for survival and fertility. As a result a much smaller proportion than normal of the offspring of such a match will survive and reproduce. The reverse is not true in the above case, but there are other jumping genes which do interfere with such matings. The result of such behavior is that a mating barrier developes between populations of the same species. This barrier makes mating with the other population disadvantageous and thus provides a selective advantage to those flys that can recognize their own group. This in turn provides an advantage to those flys from one of these groups that look or act or smell(replace this line with your favorite sense) different than the other group. Thus speciation can occur by branching off from a larger population WITH NO SELECTIVE ADVANTAGE. In the case of Drosophila, which produce many generations per year and are very prone to mutation and variation this reduction in effective population size can easily lead to rapid divergence of the two populations into two very similar but distinct species. We would thus observe two sexually incompatible but nearly identical species. In the case of Drosophila melanogaster and its closesly related "sibling species" there are examples along a continuum from freely interbreeding populations to distinct species. Some of these species diverged as recently as a few thousand years ago, some several million years ago. Thus we can formulate a TESTABLE model which predicts that speciation can occur independant of selection and lead to smaller effective populations which selection can operate much more effectively upon than it can on the species as a whole. This model also has the advantage of explaining the split between small gradual changes and large abrupt changes (microevolution and macroevolution >which is so often picked on by creationists< ) based on the population size in which advantageous mutations occur. I know, I got a little carried away there with the technicalese, but you know what I mean. When I refer to the ideas above as a model I mean that they are ideas in the process of verification. I don't expect that all of them will be verified, but as more is learned some of the above will be dropped, some will be refined and some will turn out to be right as they are presented. The existance of these genetic elements in bacteria has been known for less than 20 years, while their existance in higher organisms has only been known for about ten. There is a great deal of corroborating evidence for the model presented above for speciation, but most of it is in the form of primary sources: research reports written for other researchers in the same field, and is thus somewhat dense. I'm looking around now for a more digested form of the evidence and if I find it I will post it to the net. If not, I will post my primary sources with explanations. On another note you may have noticed, I have presented a model for the origin of new species. It has virtually nothing to do with evolution other than providing it with isolated populations to operate upon. There is a similarly vast distinction in modern scientific thought between theories dealing with the origin of life on earth and those attempting to explain the subsequent divergence of form and speciallization of function and habitat that must be explained by some theory of evolution. The one currently in place (and there for over 100 years) works pretty well as a basic theory, but it never really was intended to be all encompassing. Indeed, it is starting to appear that there may have been more than one occurance of the origin of life, perhaps as many as three which were eventually successful, and many more may have occured and not lasted very long, but no scientifically valid theory would attempt to explain the current diversity of life in terms of a single divine creation. If you want to argue for such divine creation you should argue for it at the beginning, where the actual knowledge is shakier. I think though that even that may become clearer by the end of this century. You may have noticed that I don't have the same faith in these models and theories as many creationists seem to have in theirs. That has a lot to do with the fact that science is not dependant on faith, but rather on doubt, since faith may make you content, but doubt may make you look for better explanations. This is already too long, I hope someone somewhere takes the trouble to read it and reply, I'm interested in how it will sit with people on the net. SCIENCE LIVES! Michael Lonetto PHRI
keithd@cadovax.UUCP (Keith Doyle) (04/30/85)
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The interesting article on drosophilia (sp?) brought to mind an interesting
issue, that of sexual reproduction. Sexual reproduction could certainly be
a means of propogating useful mutations througout a society, thereby increasing
a society's chance of adapting to changes in environment. It also has the
effect of selecting for individuals who have a high success of mating. This
as has been said before, is a good evolutionary explanation for 'useless'
features that may birds have for example (peacock feathers, brightly colored
birds etc.). How do creationists view sexual reproduction? (it's purpose
I mean).
Keith Doyle
# {ucbvax,ihnp4,decvax}!trwrb!cadovax!keithd