Evolution of Snake Venom
In related news, it seems that the evolution of snake venom is not so mysterious either:
This study analyzed the origin and evolution of snake venom proteome by means of phylogenetic analysis of the amino acid sequences of the toxins and related nonvenom proteins. The snake toxins were shown to have arisen from recruitment events of genes from within the following protein families: acetylcholinesterase, ADAM (disintegrin/metalloproteinase), AVIT, complement C3, crotasin/ defensin, cystatin, endothelin, factor V, factor X, kallikrein, kunitz-type proteinase inhibitor, LYNX/SLUR, L-amino oxidase, lectin, natriuretic peptide, nerve growth factor, phospholipase A2, SPla/Ryanodine, vascular endothelial growth factor, and whey acidic protein/secretory leukoproteinase inhibitor. Toxin recruitment events were found to have occurred at least 24 times in the evolution of snake venom. Two of these toxin derivations (CRISP and kallikrein toxins) appear to have been actually the result of modifications of existing salivary proteins rather than gene recruitment events. One snake toxin type, the waglerin peptides from Tropidolaemus wagleri (Wagler's Viper), did not have a match with known proteins and may be derived from a uniquely reptilian peptide. All of the snake toxin types still possess the bioactivity of the ancestral proteins in at least some of the toxin isoforms. However, this study revealed that the toxin types, where the ancestral protein was extensively cysteine cross-linked, were the ones that flourished into functionally diverse, novel toxin multigene families.
Sorry about the technical language. That's the abstract of a brief article by Bryan Fry, of the university of Melbourne, Australia. The more approachable version can be found in this article from The New York Times, by Carl Zimmer:
Ultimately, this rush is not what drives Dr. Fry, who is 34. His goal is to decipher the evolution of snake venoms over the past 60 million years. Reconstructing their history will help lead to medical breakthroughs, Dr. Fry believes. For the past 35 years, scientists have been turning snake venoms into drugs. Just this February, Dr. Fry and his colleagues filed a patent for a molecule found in the venom of the inland taipan that may help treat congestive heart failure.
Understanding the evolution of snake venoms will speed up these discoveries immensely, Dr. Fry predicted. “You need a good road map to get your research going,” he said.
And from later in the article:
Dr. Fry has constructed evolutionary trees of these venom genes, and his results indicate that venom actually evolved only once in snakes. It started out being produced at low levels, as illustrated today by garter snakes. Later some lineages evolved a more deadly bite.
“It's been the most important adaptation in the history of snakes,” Dr. Fry argued. The snakes that evolved venom no longer had to rely solely on constriction or other ways of physically subduing their prey. “It's freed them up from having to be big-muscled and slow-moving and killing their prey using constriction,” he said. “They can be light, agile, athletic, and they can occupy any niche from the bottom of the ocean to the top of the tallest tree.”
Dr. Fry's research has also shed light on the origin of venom molecules. A number of researchers have suggested that venom toxins are modified saliva proteins. They point out that ordinary saliva proteins are able to start breaking down food in the mouth. Perhaps some tinkering was all that was necessary to turn them into lethal poisons.
As Dr. Fry reports in the March issue of Genome Research, the DNA of venom genes goes against this idea. He constructed evolutionary trees of 24 venom genes, searching through online databases for their closest relatives among nonvenom genes. In only two cases did he find that venom genes evolved from saliva genes. In almost all the other cases, venom genes evolved from ones that were active outside the venom gland - in the blood, for example, as well as the brain and liver.
The evidence indicates that the evolution of a typical venom gene may begin with the accidental duplication of a gene that is active in another organ. In a process known as gene recruitment, one of these copies then mutates in such a way that it begins producing proteins in the venom gland.
In some cases, these borrowed proteins turn out to be harmful when injected into a snake's prey. Natural selection then favors mutations that make these proteins more lethal.
When I look at what actual biologists do I find them working their tails off to solve actual problems of potential importance to people's day-to-day lives. I find them using evolutionary theory as a tool for guiding them towards research projects that are likely to yield fruit.
When I look at what ID folks do, I see them desperately trying to make a virtue out of ignorance. I see people who make no attempt to do any sort of actual science based on ID, and who devote their lives to tearing down the work of others. They do this solely because their weak faith in God can only be maintained by finding scientific gaps for Him to fill. Pathetic.