Cairber wrote:I'm currently on a temp ban from the site :D , but I'll try to reconstruct (you need 100 posts to access to debate boards or I would just link)
Typical.
The thread was about "Since when is evolution fact?"
The best way to go about this takes a bit of scientific knowledge, yes, but it's fairly simple to explain.
Evolution, in regards to biology, can be broken down into five distinct parts. Two are fact, two are theory, the fourth is hypothesis. That is, one is something directly observable and repeatable, and obvious to any comer.
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A fact of evolution is the most basic definition - the change in allele frequency over time (you could say generations, but that's misleading especially in regards to single-celled organisms).
* An allele is a specific type of a gene. For example, if one gene governed eye color, it would have brown, blue, green, etc. alleles.
The simplest example of this is skin color. There are six genes that govern skin color, and they can range from all being defective (albinism) to all producing black pigment (Basque Africans), with a few others in between (even white skin has active pigmentation).
It's fairly obvious that, even without mutation, the relative frequency of these will change. Since this is observed, this is a fact, and not a theory. We take population statistics on people's ethnicity, inheritable genetic diseases, etc. and observe these changes in humans as well as numerous other species.
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The other fact of evolution is mutation. There are several kinds of mutations, the main ones I recall off the top of my head are
* Phase shift mutations (where an extra bases are added, shifting the entire rest of the chromosome's genome one step) are almost always fatal, and responsible for a good portion of near-immediate miscarriages.
* Recombinations occur during cell mitosis (splitting). Basically, as you know, everyone has two copies of a given chromosome. During their split, they get broken up into thousands of different chunks, and they don't always recombine with the same 'host' as it were. Given the amount of junk DNA in a typical modern higher animal, this tends not to change much.
* Point mutations are the most common, about 80% of all mutations according to my biology teacher. Basically, they are an error in the genetic copying process, resulting in a thymene being replaced by a glutemine, for example. On average, people possess roughly 100 point mutations.
** All primate DNA has 3 billion base pairs. Given a half million generations between us and Chimpanzees, that's 50 million point mutations, or roughly 1.5%, which is in line with difference estimates. Be careful not to fall into the trap of creationists claiming only 1 or 2 meaningful mutations have occurred - that is after you take into account that 96% of DNA is junk and that a triplet has 64 codes but only 20 protiens to code for.
* Splits occur when one chromosome splits into several. This happens in plants fairly frequently, less so in higher animals, I'm not aware of any particularly notable examples.
* Fusions occur when chromosomes combine. Again, this happens a lot in plants, though the human #2 chromosome is a fusion of the (IIRC) #3 and #5 chromosomes in other great apes.
* Chromosomes can also be deleted (generally fatal) or be duplicated (sometimes okay). The most well-known example of this is gene 21 trisomy, better known as Down's Syndrome. Less deleterius examples are females with three X genes or males with two Y genes.
* Some viruses will actively insert themselves into the DNA of hosts, which will sometimes infect germ lines and effectively become a part of the host's permanent DNA. This is generally most useful for determining when species branched apart, as the virus is usually rendered inert. However, it does provide more genetic material which might provide a useful mutation in the future.
...that's all I can recall off the top of my head, anyway.
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One theory involved in evolution is the theory of natural selection - survival of the fittest, et. al. This is obvious to most people so I won't belabor the point.
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The more contentious theory of evolution is that of common descent. Or more appropriately, since common descent for some species (speciation) has been observed, the theory that all species arose from the same organism.
It's called a theory and not a fact because, of course, we haven't directly observed said origin. However, it's called a theory and not a fact because there is overwhelming evidence to support it. Most notably is this: There are certain genetic functions required for all life. These functions could have taken a great many forms - as I said above, a triplet has 64 potential codes, but only codes for 20 proteins. There are trillions of possible combinations.
And yet, with the sole exception of a single bacteria, which only differs in this regard by one single mutation, every species so far discovered on Earth has these exact same base sequences. This fact, combined with the viral insertion data from above, is very powerful evidence for common descent.
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The hypothesis in evolution is the creation of life itself - ie abiogenesis. Biologists usually separate it from evolution per se, because it's a whole 'nother ballgame. However creationists and laypeople tend to combine the two, so its inclusion is linguistically inevitible. Anyway, despite not being proven yet, there is still strong evidence for it:
1: Lipid bubbles (cell membranes) and basic genetic material formed readily in Earth's early environment.
2: There is significant evidence of an RNA world that was present before the rise of DNA (a very simple change, but an important one due to higher stability), and Pre-RNA before that (where different bases were competing presumably on efficiency grounds).
There are other, known steps bridging points 1 and 2, but as far as I understand it, the gulf is still pretty vast. That components for life would develop in a given atmosphere is fact (we observe it), that certain components formed in a certain way is theory (there is evidence for it), that the entire thing happenned, at this point, is merely a very strong hypothesis.
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Regarding Intelligent Design, if it is to be accepted as science, it must first be formulated as a testable hypothesis. For an example of a semi-alternative to evolution that has had some success in this regard, see the Gaia Hypothesis.
, but I'll try to reconstruct (you need 100 posts to access to debate boards or I would just link)
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