Talk:Last universal common ancestor/Archives/2007/April

Source?

Does anyone have a citation for the claim that LUCA lived around 3.5 billion years ago? I'd like to use it for History of Earth. — Knowledge Seeker দ 00:07, 29 March 2006 (UTC)

"The Last Universal Ancestor hypothesis has since been refuted on many grounds[citation needed]. For example, it was once thought that the genetic code was universal (see: universal genetic code). Back in the early 1970s, evolutionary biologists thought that a given piece of DNA specified the same protein subunit in every living thing, and that the genetic code was thus universal. Since this is something unlikely happen by chance, it was interpreted as evidence that every organism had inherited its genetic code from a single common ancestor, aka. the "Last Universal Ancestor." In 1979, however, exceptions to the code were found in mitochondria, the tiny energy factories inside cells. Biologists subsequently found exceptions in bacteria and in the nuclei of algae and single-celled animals. It is now clear that the genetic code is not the same in all living things, and that it does not provide powerful evidence that all living things evolved on a single tree of life[citation needed]. Further support that there is no "Last Universal Ancestor" has been provided over the years by lateral gene transfer in both prokaryote and eukaryote single cell organisms. This is why phylogenetic trees cannot be rooted, why almost all phylogenetic trees have different branching structures, particularly near the base of the tree, and why many organisms have been found with codons and sections of their DNA sequence that are unrelated to any other species[citation needed]."

- I am very suspicious of this paragraph. It has no sources cited, and it does not match up at all with what I was taught in multiple University level Biology classes (Including Cellular, and Microbiology). I was taught that all known exceptions to the universality of the genetic code were believed to be acquired characteristics. Most of them are also attributable to post translational modification as well (such as the presence of Selenocysteine in mammals.Cadallin 20:50, 1 April 2007 (UTC)Cadallin

I have a page "Last Common Ancestor" so I put in a link to it, but no trail, so I will sign it here. Also whoever put in the text above about the refutation also put it in Last Common Ancestor reference section where I really don't think it belongs. Tom Schmal 22:54, 9 April 2007 (UTC)