Friday, May 29, 2009

LUCA

Before the advent of gene sequencing, the theory of evolution was based on morphology (physical characteristics). Then, scientists developed methods to find the make-up of the gene. The gene is made of a set of 4 molecules which repeat, which we call nucleotides. They have names but we’ll call them A, T, C & G. These nucleotides combine in an order that acts as a code, which is read by other cell units and turned into proteins which do much of the work of the cell.

The National Center for Biotechnology Information (NCBI) is taking the sequences found by researchers all over the world and comparing them. Many of these sequences are done on small organisms of single cells. Bacteria were considered the only organisms to be of one type of cell, the prokaryote (pro-CARry-oat) type. In the 1970’s, scientists realized there was another type of prokaryote, called archaea (ar-KEY-ah). They were considered a separate domain from bacteria and a third one, eukaryotes (you-CARry-oat). The third type is the one in plants and animals, including humans. To make things more complicated, each of the domains have branches, so they need to find common ancestors to the branches for each of the 3.

Unfortunately for the advocates of Darwinian evolution, the results of the sequencing have shown anything but a clear-cut progression from an organism which can be considered the simplest to the next which is more complex and on up to human scale. I will talk more about that next week. But the point is important because it moves the search "back" to a previous ancestor that would have shared genes of all of them and been able to branch off into the 3 distinct domains we see now.

In a paper, "Clusters of orthologous genes for 41 archaeal genomes and implications for evolutionary genomics of archaea," published by Eugene Koonin et al., they discuss the findings of comparitive gene studies (orthologous means genes that come from a common ancestor. The conclusion for the archaeal branch is:
Genomic reconstructions suggest that the last common ancestor of archaea might have been (nearly) as advanced as the modern archaeal hyperthermophiles.
They estimate it would have had to have at least 996 genes. As they say, it is almost as complex as modern organisms. And archaea are believed to have been present as long as 3.5-3.8 billion years ago. Where then does the common ancestor of all organisms fit? They are running out of back time for all the gene sequences to fall into place, because some scientists think the Earth was too hot for organisms to form until around 4 billion years ago.

Next time, for my last regular ID entry, I will talk about the NCBI results which show the end of Darwinian evolution before it even begins.

Update 1/20/2013: My interest in Intelligent Design Theory (ID) has changed to what is called "Special Creationism," the belief that God created species, including humans, separately and directly. Much of the biological science in ID is similar to Special Creationism.

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