Evolutionary Biologist Andreas Wagner: We "Know Little" about How "Innovations Originate"
At his lab's website, University of Zurich evolutionary biologist Andreas Wagner acknowledges that "Biologists know many fascinating examples of evolutionary innovations, and they know that natural selection can preserve an innovation once it has originated. However, they know little about the principles that allow innovations to originate in the first place." A press release from the Santa Fe Institute, about a new Nature paper co-authored by Wagner, states much the same thing: "Exactly how new traits emerge in evolution is a question that has long puzzled evolutionary biologists." ENV reported on this earlier, but it merits further consideration.
Writing in Nature, Wagner says: "How evolutionary adaptations and innovations originate is one of the most profound questions in evolutionary biology." According to the title of the release, "Most traits emerge for no crucial reason." In other words, as I discussed in a recent podcast with Discovery Institute fellow Cornelius Hunter, the idea is that complex traits arise thanks to sheer dumb luck. So as a proposed evolutionary mechanism, how plausible is that?
According to the statement from Santa Fe Institute, Wagner's study "subjected the complex metabolic chemical process" involved in E. coli metabolism "to a 'random walk' through the set of all possible metabolisms, adding one reaction and deleting another from it with each step." They maintained the ability of the bacterium to survive on glucose, "but allowed everything else to change." According to the statement, "They found that most metabolisms were viable on about five other carbon sources -- sugars, building blocks of DNA or RNA, or proteins -- that are naturally common but chemically distinct compounds." Their conclusion is that good fortune alone resulted in the emergence of these new traits, suggesting that exaptation rather than adaptation is important for generating evolutionary innovations. Exaptation is of course the idea that parts can be co-opted or borrowed in biological systems to perform completely different functions. Did they demonstrate that this is possible? Not really.
The study sounds impressive, until you look at it a little more closely. What exactly happened in their experiments? Well, they didn't do any experiments. Instead the team performed a theoretical computer analysis simulation where known metabolic reactions systematically deleted enzymes from the network. They found that if they simply selected for a network that required glucose, they also had the "potential" to metabolize other carbon-based food sources. As they put it:
We show that when we require such networks to be viable on one particular carbon source, they are typically also viable on multiple other carbon sources that were not targets of selection. For example, viability on glucose may entail viability on up to 44 other sole carbon sources.So they didn't actually experimentally knock out enzymes in living E. coli and determine that they could still metabolize other carbon sources. Thus, they treated metabolic pathways and interactions as discrete entities, and did not consider real-world problems, like how certain enzymes might be necessary to prevent side reactions from affecting the pathway.
But let's imagine, for the sake argument, that a real-world experiment along these same lines were to reveal the same results: that randomly modified metabolic networks in E. coli are randomly capable of metabolizing various carbon sources. Would that demonstrate that random changes to metabolic networks can easily generate novelty? Not necessarily.
Wagner's paper in Nature concluded that "Our observations show that latent metabolic abilities are pervasive features of carbon metabolism." From an ID-based view, perhaps these abilities aren't latent at all.
Perhaps E. coli are designed with a robust network of hundreds of enzymes potentially capable of metabolizing many different carbon sources. Keep in mind what Wagner's simulation did: It selected portions of these metabolic networks with the only constraint being that the network should retain the ability to metabolize glucose. In other words, they weren't starting with a functionless system and finding that new functions arose, they were starting with a function-rich system and found that even when you delete a lot of parts, multiple functions remain.
If these metabolic networks are designed to be inherently robust, capable of metabolizing many different food sources, then even if you select only "random networks that were viable on glucose as the sole carbon source" (as the paper said they did), then it would not be surprising to find that some other similar carbon sources might also be potential metabolic targets of the network.
In that case, what Wagner's study actually measured might be how resistant these robust networks are to loss of functions that were already present, not how they can "randomly" gain functions through "exaptation."
Nonetheless, defenders of the idea of unguided evolution are excited about the prospect that luck alone can produce viable functional new pathways. At his blog "Darwin's God," Cornelius Hunter observes that after the publicity surrounding Wagner's recent paper:
[L]eading science writer Carl Zimmer, as if on cue, writing for Scientific American on the topic of "how organisms can evolve elaborate structures," informed his readers that when it comes to complexity "To some extent, it just happens," and that "intricate systems of proteins can evolve from simpler ones," and finally that "studies suggest" that random mutations "can fuel the emergence of complexity."When materialists are reduced to asserting that complex function "just happens" for "no crucial reason," I think we can see this as a vindication of intelligent design theory with its view on the impotence of unguided evolutionary mechanisms.