The Edge of Horizontal Gene Transfer
|October 22, 2007||Posted by Patrick under Intelligent Design|
Horizontal Gene Transfer (HGT) is now being invoked fairly often as a magic wand by Darwinists. So what experimental evidence do we have?
Horizontal gene transfer, in which genetic material is transferred from the genome of one organism to another, has been investigated in microbial species mainly through computational sequence analyses. To address the lack of experimental data, we studied the attempted movement of 246,045 genes from 79 prokaryotic genomes into Escherichia coli and identified genes that consistently fail to transfer. We studied the mechanisms underlying transfer inhibition by placing coding regions from different species under the control of inducible promoters. Our data suggest that toxicity to the host inhibited transfer regardless of the species of origin and that increased gene dosage and associated increased expression may be a predominant cause for transfer failure. While these experimental studies examined transfer solely into E. coli, a computational analysis of gene transfer rates across available bacterial and archaeal genomes supports that the barriers observed in our study are general across the tree of life.
To summarize, they tested a small subset of the genes that were classified as nontransferable (0.6%). Out of the genes they tested, 80% could not be artificially transferred when in an active state, most of which were related to the ribosome. So, this would suggest that less than 0.5% of genes were toxic. However, from what I’ve read elsewhere things are even more grim for HGT as a Darwinian mechanism for major innovation when it comes to higher species.
Type III secretion systems (TTSS) are unique bacterial mechanisms that mediate elaborate interactions with their hosts. The fact that several of the TTSS proteins are closely related to flagellar export proteins has led to the suggestion that TTSS had evolved from flagella. Here we reconstruct the evolutionary history of four conserved type III secretion proteins and their phylogenetic relationships with flagellar paralogs. Our analysis indicates that the TTSS and the flagellar export mechanism share a common ancestor, but have evolved independently from one another. The suggestion that TTSS genes have evolved from genes encoding flagellar proteins is effectively refuted. A comparison of the species tree, as deduced from 16S rDNA sequences, to the protein phylogenetic trees has led to the identification of several major lateral transfer events involving clusters of TTSS genes. It is hypothesized that horizontal gene transfer has occurred much earlier and more frequently than previously inferred for TTSS genes and is, consequently, a major force shaping the evolution of species that harbor type III secretion systems.
Notice that HGT is also used as a workaround to claim that the type III secretion system appeared in nature before the flagellum. Which of course is in competition with the scenario preferred by ID proponents by which the flagellum came first and the TTSS derived from it. But even going with the scenario the Darwinists prefer the same complex mechanism has to evolve at least TWICE (as in, evolved once and transferred successfully in a functional state that gives survival advantage). Note that HGT is only a method for transferring previously derived information, not the source of the information itself. The hope is that combinational effects will do their magic.
We can look to the National Research Council to see why this is important:
“Natural selection based solely on mutation is probably not an adequate mechanism for evolving complexity.
More important, lateral gene transfer and endosymbiosis are probably the most obvious mechanisms for creating complex genomes…”
Now that we have actual experimental data we can apply them to previous speculations. Back when Behe’s Edge of Evolution came out I commented that the next step for ID researchers is to do experiments to discover the exact limitations of all proposed Darwinian mechanisms. I’d specifically like to see researchers artificially transfer the genes related to the flagellum to other species and see if they help, kill, harm, or inhibit the new hosts. As this data indicates, they are likely to be “capable” of being transferred in general but that still does not validate their story-telling. Also, while research related to ID icons like the flagellum are interesting I’d rather see further research into the limitations of HGT when it comes to higher species.