Evolution V Creation

[Tiberius]

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...

Please provide the evidence that leads you to be able to distinguish between:

1) All life has a single common descendant.

2) Some of life has one common descendant and some of life has a different common descendant.

In other words, a single common descendant compared to two common descendants.

Since you say that the evidence only supports 1) but not 2), I want to know what that evidence is.

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).