Xenogenesis,
Maybe it wasn't the most appropriate statement, considering
there is evidence for a common ancestor. I'll get to that in a minute but first let's have a look at what you are saying:
Paraphrasing, you say: "There is no [fossil] evidence for a common ancestor, and therefore there
was no common ancestor. On top of this, because no common ancestor has been found the entire theory of evolution falls down!" All of these conclusions are based on a percieved
lack of evidence.
Which leads me onto the molecular evidence. I apologise in advance if you are familar with this, and it is a bit simplified, but I don't know your level of knowledge so I've tried to keep it basic:
It all revolves around the way that DNA codes for proteins (known as translation), its' a bit long-winded for a short(ish) post, but basically three letters code for each amino acid in a protein sequence. This is the same code for
all life. There are a few minor variations, but essentially if you take the human sequence for insulin and put it into an
E. coli you will get the same protein produced. I repeat,
this is common for all life!
The central player in translation (ie where it all happens) is called the ribosome. This is a complex of protein and RNA, and is of course common to
all life. By comparing the sequence of the RNA component of the ribosome (ribosomal RNA [rRNA]) for all of the organisms you know, you can't escape the conclusion that they all derived from a common ancestor. It also throws a few extra pieces of information: like the fact that Archea are closer related to Eukaryotes than Eubacteria are, and that the mitochondria (that are in all Eukaryotes) are closely related to a subsection of the bacterial domain.
Hope this is clear enough, and I'm sure you have lots to say about it.
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