Evolution V Creation

[rjh4 is back]

The definition of a species is one that can successfully breed with another. That is to say that if one animal can have offspring with another then they will (normally) be classified as the same species.

Not necessarily. For example, even the article provided by Min said: "No exact rule exists for deciding when a group of animals constitutes a separate species." I would be quite surprised if the new species in the articles was incapable of breeding with the other tanagers even though they might not breed with them and yet the scientists in the article called the birds a new species. There was no indication in the article that the new species couldn't interbreed with other tanagers, just that they didn't possibly because of their songs. See also Species and some of the difficulties with that sort of definition, particularly "ring species".

Now, the term species may well be a human invention but the fact that these differentiations exist in the first place is entirely natural. We simply observe them and give them names. So it is not man who decides what is or is not a new species at all. It is man who observes these clear and natural differences in the animal kingdom and gives them titles. They exist independently of our interpretation.

As seen in the wiki article above, it is not quite so easy as you make it out to be as scientists cannot always tell when two groups can potentially mate. So it is still scientists that make a decision.

A conclusion of descent of all life from a single common ancestor is the most rational view as so far we have not come across a single life form that cannot in some way be shown to be biologically related to any other. If, as you seem to be suggesting, there are many groups of organisms on this world that can trace their ancestory back to completely different abiogenesis then we would see this in the biological world as it would be obvious. The simple fact that an oak tree can 'read' the dna of a shrimp must tell us something about the family history of life on Earth.

All living things on this world have their genome either in the form of DNA or RNA. That must have originated from a single common ancestor. If you can provide proof of any organism that does not use this template or suggest how, out of the billions of possible carbon/protein bonds etc. this particular solution was used by totally separate examples of abiogenesis then I'd like to hear it.

So, to summarise, we are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances.

I have no idea why you brought up abiogenesis as that was never part of the discussion. Furthermore, why do you assume in my question that at least one of the two original life forms had to use something other than DNA or RNA? I want to know what evidence would distinguish between all life descending from a single anscestor and part of life descending from one anscestor and the other part of life descending from a second anscestor, where the two anscestors both use the same template (as you put it). None of your comments addresses this issue. And if there is no such evidence that necessarily distinguishes between the two, then it would seem that common descent merely assumes only one anscestor (the use of a common template does not necessitate a conclusion of common descent from a single anscestor).

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I think you should remember though, Adrian, relative to speciation, it is man that decides what is a new species, there is no transcendant objective standard.

Erm...we decide what a new species is based on whether it can reproduce successfully with similar organisms. For instance, donkeys and horses are separate species because although they can produce offspring (mules), those offspring are sterile. We don't have an transcendant objective standard, but that doesn't mean we don't have a very strict standard at all. Technically, no "species" exist...it's just a human way of looking at and identifying different animals. There isn't an objective way of doing this since we made up the idea in the first place.

So just like a scientist could look at the slight differences in those birds and decide they are all different species, a scientist could look at the slight differences in humans and conclude there are different species of humans.

No they can't. This isn't how scientists do it these days. Classification has moved on since the days of Darwin! Yes, Darwin looked at the finches and thought they were all different species because they looked different, but when he got back from his voyage, a bird expert corrected him and told them that they were all the same type of bird. This was the idea that got him thinking about evolution in the first place. I'm afraid you are very much mistaken if you think that "slight differences" make scientists conclude "different species".

As for me, I would just say that there are birds that differ from each other and there are humans that differ from each other.

Yes, and yet there are some birds that cannot mate successfully with other birds, and we call these different species. You are making a bad comparison because birds are a single class (Aves) that contain numerous species, whilst humans are a single species (homo sapiens). If you want to compare the two, you'd have to point to a specific species of bird (i.e. Finch) rather than use the entire class.

Still none of these changes (whether or not one calls it speciation or not) necessitate a conclusion of descent of all life from a single common anscestor.

Of course they don't...nobody is arguing that. How did you get from methods of classification to "common descent"? The two are not directly related at all...

See my comments to Dar regarding species. And I agree that classification has nothing to do with common descent. I only brought this up as the only thing I have been denying, contrary to your implication in your previous post.

To put it simply, gene sequencing. Our DNA has similarities (i.e. sections that are identical) with all other life on the planet. The theory of common descent would predict that animals that are anatomically similar would have similar DNA, and this prediction holds true across every sequenced genome. We share 95-99% of our DNA with chimpanzees / orangutans, confirming the theory that we have a common ancestor in "recent" history. With other primates, we share less DNA, showing that chimpanzees are (as far as we know) our closest relative. I read somewhere (and I'll try to find the article) that we are more closely related to chimps / orangutans than chimps / orangutans are related to gorillas.

Going back further, we have less in common with rodents, even less in common with retiles, even less with fish, but we do share similar DNA with all life. It is through this methods of comparing DNA that we can draw up the tree of life, comparing every animal with every other animal. If one animal didn't fit, or had differences in its DNA that didn't correspond with its anatomy and where you would predict it to go on the tree, then common descent would be ruined.

This isn't to say that there weren't multiple "first" organisms, but if there were, then from the evidence we have, one of two things must have happened. Either:

1) The other "first" organisms died out, leaving no trace of their existence (and if they were bacteria as is likely, this would be very possible).
2) At some early stage, two or more of these first strains converged and formed one strain, which then became the common ancestor of all life.

The first scenario is more likely, since the second would have to rely on the two or more first strains having genetically similar RNA in order to reproduce, and the odds of that happening when these are two different life sources are astronomical. This would also mean that reproduction by a means other than self-replication would have been in the world long before it currently appears to have been.

So going on what the evidence shows, what we can rationally say based on that evidence (and not mere speculation), there appears to have only been one common ancestor. If there were many, they would all have to be in bacterial form, and they either all died out or merged (which seems unlikely given their ways of reproduction).

So it seems your argument assumes a naturalistic explanation of the first anscestor(s) and because the odds would be astronomical for more than one anscestor having genetically similar RNA you assume there must have been only one. So the abiogenesis argument does come into play here but I think you previously indicated that it was an entirely separate issue. So while common descent may not require the assumption of a single original life form, it is assumptions that lead you there nonetheless and not necessarily the evidence alone.

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And the Physical evidence that supports the bible?

I am not quite sure what you mean by the question. Can you clarify please?