Evolution is a very commonly misunderstood term and the socio-political use of the word doesn't really match up with the scientific use, leaving things rather muddy. Even within the scientific realm there is a lot you have to specify in order to really get to what you mean by the word, it's a big discipline. It is kind of like saying "I don't believe in Physics" when really you may just be disputing the validity of String Theory or the Copenhagen Interpretation.
Getting back to macro evolution and micro evolution, those are terms commonly used outside of the discipline to distinguish between phenotypic (stuff you can see, like beak shape or fur color) change within a species over time versus the act of speciation, that is, the formation of a new species. The first kind is often called micro evolution and is really kind of a red herring because, broadly speaking, everyone has agreed on that for hundreds of years. People saw the change in heritable characteristics (those that can be passed on to children) long before the time of Darwin and Lyle. Gregor Mendel laid out the concept of what we now call Mendelian Genetics (obviously he didn't know anything about DNA), showing how heritable traits were passed on in pea plants at the same time that Darwin was publishing his work. Mendel was a priest and there was no theological trouble with his work because it was just documenting how a species passes on variation. Those who try to dispute Creationism by showing incremental evolution within a species are doing them a disservice because that really isn't the heart of the dispute at all. Then we get to what Kris is calling Macro Evolution, which is a term used to refer to the production of a new species from an existing species. This is where the dispute over "evolution" really comes into play, it isn't a disagreement about whether things evolve, it is a disagreement about speciation. Darwin called his work "On the Origin of Species" or, in the long form, "On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life". The title of his work is the key here, he wanted to show a mechanism for the creation of new species from existing species. Darwin had a couple of key insights and, put together, they are generally known as "descent with modifications and preferential survival". It works thusly: 1. In every generation, there are multiple values in a population for a heritable trait 2. Those values are not passed on with complete fidelity. Some offspring will get one value for a trait, some another value, some a value not obviously present in the parents. 3. Those values can have differential survival outcomes, ie, members with one value may be more likely to survive and pass on that value than members with another value. This, in a nutshell, forms the basis of Evolution, why species change. Darwin then went on to show that that algorithm (though he would not have called it that) can produce speciation. As a side note, people differ in their distinction on what constitutes a species. Some people take a very cut and dried line that says two populations are different species if they cannot breed and produce viable offspring. While that is the easiest way to define it, it isn't very useful in a practical context because then you have to explain why lions and tigers aren't different species. More generally, a species is usually defined as a population that is genetically and physiologically distinct and that does not naturally interbreed with another population. So while lions and tigers can mate and produce offspring, they do not do so in the wild and they form distinct populations and have important genetic and physiological differences. The bit about interbreeding, of course, goes out the window when you are talking about asexually reproducing (and especially self propagating) organisms. There are a couple different methods of speciation normally recognized. The most common kinds are called Allopatric and Peripatric speciation. These both are a result of separation of populations of a given species, usually geographically. For instance, a segmenting of the range of a species due to deforestation where the populations in the two new regions no longer encounter one another much because their range isn't contiguous any longer. These two populations start out with differences in their genetic make up that would normally be a wash when the whole population is interbreeding. However, due to the lack of ongoing contact between the populations, the differences between the pool of variation combined with the continuing process of descent with modification and natural selection can produce enough variation over many generations to make the two populations distinct enough that they not only do not but can not interbreed successfully. This is known as allopatric speciation. Peripatric speciation is a more extreme version of allopatric speciation, usually involving substantial geographic separation like the formation or colonization of islands. It is also the subject of the discipline known as Island Biogeography. Basically, there are times when otherwise unreachable spots are reached by a group of individuals, like when land bridges appear during periods of extremely low sea levels. These new populations may then be cut off again and this new, isolated, population will be characterized by having a very small pool of genetic diversity to start with. This is known as the Founder Effect. In these cases, traits which might be very rare in the parent population become much more common in the child population because of the small number of individuals contributing to the overall starting pool. The founder effect, combined with the fact that natural selection often rewards different characteristics in a small, island setting than it does on a large contiguous region, often means that these isolated populations will diverge quickly and dramatically from the parent population. Peripatric speciation is the reason why Australia largely has marsupial mammals whereas marsupial mammals are quite rare everywhere else. They got cut off early in the changes in mammalian physiology and due to low gene flow in from the outside, the trend continued there but diverged elsewhere. There are other types of speciation discussed, such as sympatric speciation. Sympatric speciation is a hotly disputed area, however, as it hypothesizes how two species can arise in the same area without substantial separation. As far as I'm aware, there aren't any instances of this type of speciation that have been shown to happen in the wild, but I haven't really studied the subject in awhile, so I'm not sure what the current state of research on sympatric speciation is. Speciation has been observed in the laboratory in a number of experiments. The most common (among animals) are with Drosophila, fruit flies, because of their short generation time, wide use in the lab and high rate of natural genetic variability. A summary of some of the instances of observed speciation can be found here: http://www.talkorigins.org/faqs/faq-speciation.html It also contains a further discussion of what constitutes a species and a discussion of the Biological Species Model. A lot to digest, I know, but hopefully it will help people thinking about the arguments around Evolution and, more specially, that we are really talking about an argument regarding speciation. Cheers, Judah On Mon, Jun 7, 2010 at 11:08 AM, Kris Sisk <[email protected]> wrote: > >>Is the dogs/wolves example even an example of evolution? Isn't it >>domestication? >> > > Domestication is usually a perfect example of that type of evolution. I think > that micro evolution is the one that would be wolves to dogs, but I never > could keep the two terms straight for some reason. Another example would be > the finches observed by Darwin just prior to writing the Origin of the > Species. They had obviously evolved differing beaks for differing purposes, > but they were all still finches. If those finches had evolved into > hummingbirds, for example, that would be macro evolution (assuming I haven't > gotten the two terms mixed up). > > Now before anyone jumps down my throat, I'm just illustrating the point. > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| Order the Adobe Coldfusion Anthology now! http://www.amazon.com/Adobe-Coldfusion-Anthology-Michael-Dinowitz/dp/1430272155/?tag=houseoffusion Archive: http://www.houseoffusion.com/groups/cf-community/message.cfm/messageid:320569 Subscription: http://www.houseoffusion.com/groups/cf-community/subscribe.cfm Unsubscribe: http://www.houseoffusion.com/groups/cf-community/unsubscribe.cfm
