Contingency and the Structure of Lifes Building Blocks
Some Yale scientists found they could construct protein-like molecules using amino acids of a type not found in living things. They found that beta-amino acids can fold into shapes similar to the proteins made of alpha-amino acids used in living things. Beta-amino acids have an extra carbon on the backbone. “Yale chemists show that nature could have used different protein building blocks,” reads the title. One of the researchers said, “The structure we see is intriguing, as it suggests that natural proteins could have been composed of beta-amino acids, but were not chosen to do so.” Who did the choosing was left unstated.
Another press release from Howard Hughes Medical Institute argued that man-made proteins made of beta-amino acids might work as effective pharmaceuticals, because they would not be degraded by the enzymes in living cells. The article mentions that cells actually synthesizes certain beta-amino acids but does not use them in protein construction. The fact that cells have not avoided them entirely “raises a thorny biological question,” the press release says. Why don’t beta-based proteins exist in living cells? For now, the choice seems arbitrary. Clearly, protein-like structures can be formed from them. Jack Szostak of HHMI commented, “the implication is that biology uses its standard macromolecules not because they are uniquely suited to their tasks, but at least in part because of other considerations, such as ease of synthesis, or possibly historical accident.”
This finding raises interesting questions in the philosophy of biology. Some evolutionists have tried to claim that the environment forces life down certain pathways, making life as we know it nearly inevitable. Here, though, there don’t seem to be any constraints against the use of the beta types. In addition, there are many dozens of other types of amino acids not used by life. Having amino acids of all one hand appears to confer an advantage. Related studies have investigated whether DNA is the only feasible carrier for the genetic code. (So far, DNA seems to have clear physical advantages over its competitors.) But if the choice is between objects as similar as a Ford and a Chevrolet, why would a mindless material world stick with one brand all the time?
Experiments like this are worthwhile to flesh out our conceptions of what is possible. Do we live in the “best of all possible worlds” at the molecular level? Or could eagles, giraffes and fish exist just as comfortably in a beta-amino-acid world? Presumably so, if all the functions of a cell could be carried out as well with beta brand. This would be a strike against the environmental determinists. Though much remains to be understood, it appears that a “choice” was made to go with the alpha-amino acids. The more that contingency is seen at the basic levels of life, the less probable are repeated appeals to “frozen accidents” and the more plausible it becomes that choices were made by a Designer.