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Evolution With and Without Multiple Simultaneous Changes

William A. Dembski
Photo: Plasmodium falciparum, by Dr Graham Beards, CC BY-SA 4.0 , via Wikimedia Commons.

I am reviewing Jason Rosenhouse’s new book, The Failures of Mathematical Anti-Evolutionism (Cambridge University Press), serially. For the full series so far, go here.

Darwinism is committed to evolution happening gradually, one step at a time, by single mutational changes. There’s a sound probabilistic rationale for this view, underwritten by, or one might say in reaction to, specified complexity. The alternative to single mutational changes is multiple simultaneous mutational changes. If simultaneous changes were required of evolution, then the steps along which Darwinian processes move would become improbable, so much so that Darwinian evolution itself would no longer be plausible. Darwin put it this way in the Origin of Species: “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case.”

“Small Mutational Steps”

Of course, Darwin didn’t just mean numerous, successive slight modifications as such. What, after all, can’t be formed gradually in the absence of any constraints — any system of parts can, in principle, be built up one part at a time, and thus gradually. For Darwin, the constraint, obviously, was natural selection. The slight modifications acceptable to Darwin were those where each modification confers a selective advantage. Darwin was, after all, in this passage from the Origin defending his theory. Like his modern-day disciples, he was convinced that all evolutionary change happens gradually, with natural selection approving every step of the process. In our day, those changes are seen as mutational, and the most gradual of these is the single mutational change. Jason Rosenhouse buys into this view when he remarks, in a passage already quoted in this series, that all adaptations in biology “can be broken down into small mutational steps.” ( p. 178)

To overturn the view that all biological adaptations can occur through single mutational changes, one baby step after another, it is therefore enough to show that some adaptations resist gradual formation in this way and instead require multiple simultaneous changes. Earlier in this review, I pointed to irreducible and specified complexity as providing counterexamples to Darwinian evolution, urging that these pose a convincing barrier to natural selection acting on random variations. I want now to probe deeper into this barrier, and specifically how the work by some of my colleagues and me regarding the need for multiple simultaneous changes in evolution rebuts Rosenhouse’s case for Darwinian gradualism. 

The Challenge

To understand the challenge that multiple simultaneous mutational changes pose to Darwinian evolution, let’s revisit evolution on the discrete hypercube (see here). Evolution in this case starts from the state of all zeros, i.e., (0, 0, …, 0) and ends at the state of all ones, i.e., (100,100, …, 100). Evolution proceeds by going from one path element of the hypercube to the next, querying up to 200 neighbors, with the probability of finding the next path element being 1 in 200 for each query. As noted already, this is a geometric progression, so the average number of queries per successful evolutionary step is 200, and since the total path has 10,000 steps, the average number of queries, or the waiting time, to go from (0, 0, …, 0) to (100,100, …, 100) is 2,000,000. There are bacteria that replicate every 20 minutes. So with life on earth lasting close to 4 billion years, that puts an upper limit of about 100 trillion generations on any evolutionary lineage on planet earth. So 2,000,000 is doable.

But what if evolution on the hypercube required two simultaneous successful queries — of one neighbor and then the next — for the next successful evolutionary step? Because the queries must be successful simultaneously, they are probabilistically independent, and the probabilities multiply. So, the probability of two simultaneous queries is 1/200 x 1/200, 1 in 40,000. Granted, each step now traverses two neighbors, so the total number of steps needed to get from (0, 0, …, 0) to (100,100, …, 100) drops in half to 5,000. But the total waiting time to get from (0, 0, …, 0) to (100,100, …, 100) is now 40,000 x 5,000, or 200,000,000. That’s a hundred-fold increase over non-simultaneous queries, but still less than 100 trillion, the maximum number of generations in any evolutionary lineage on earth.

But Let’s Now Ramp Up

What if evolution on the hypercube required five simultaneous successful queries — of one neighbor, then another, and another, and another, and still one more — for the next successful evolutionary step? Because the queries must be successful simultaneously, they are probabilistically independent, and the probabilities multiply. So, the probability of five successful simultaneous queries is 1/200 x 1/200 x 1/200 x 1/200 x 1/200, 1 in 320 billion. Each step now traverses five neighbors, so the total number of steps needed to get from (0, 0, …, 0) to (100,100, …, 100) drops to 2,000. But the total waiting time to get from (0, 0, …, 0) to (100,100, …, 100) is now 2,000 times 320 billion, or 640 trillion. That’s a 320 million-fold increase over non-simultaneous queries. Moreover, this number well exceeds 100 trillion, the maximum number of generations in an evolutionary lineage on earth.

As is evident from this example, if evolution requires simultaneous successful queries (aka simultaneous mutational changes), then Darwinian evolution is dead in the water. In that case, the waiting times (which correlate precisely with improbabilities) simply become too great for evolution to do anything interesting. Now granted, the hypercube is a toy example. But real-life examples of evolution exist that seem to require not successive, but simultaneous mutational changes. Mike Behe examined one such example in detail in his second book, The Edge of Evolution (2007). There he noted that two particular amino acid changes, which call for associated genetic changes, were implicated in the malarial parasite Plasmodium acquiring chloroquine resistance. These changes are rare, and in line with the need for simultaneous mutational changes. In particular, resistance to chloroquine occurs in these malarial parasites roughly 1 in 10^20. Those numbers are disconcerting for a smooth-sailing Darwinian evolutionary process. 

Even so, Rosenhouse, citing Kenneth Miller, remains unconvinced (see pp. 157–158). But as is Rosenhouse’s habit in Anti-Mathematical Evolutionism, he always gives critics of intelligent design the last word. Miller charges Behe with artificially ruling out cumulative selection and thus with failing to nail down the case for simultaneous mutations. But Darwinists, in defending cumulative selection, require critics to identify and rule out every possible evolutionary pathway, an effectively infinite and therefore impossible task. Behe’s response to Miller, which Rosenhouse leaves unmentioned, is instructive. I quote it at length:

In general Darwinists are not used to constraining their speculations with quantitative data. The fundamental message of The Edge of Evolution, however, is that such data are now available. Instead of imagining what the power of random mutation and selection might do, we can look at examples of what it has done. And when we do look at the best, clearest examples, the results are, to say the least, quite modest. Time and again we see that random mutations are incoherent and much more likely to degrade a genome than to add to it — and these are the positively-selected, “beneficial” random mutations.

Miller asserts that I have ruled out cumulative selection and required Plasmodium falciparum to achieve a predetermined result. I’m flattered that he thinks I have such powers. However, the malaria parasite does not take orders from me or anyone else. I had no ability to rule out or require anything. The parasite was free in the wild to come up with any solution that might help it, by any mutational pathway that was available. I simply reported the results of what the parasite achieved. In 10^20 chances, it would be expected to have undergone huge numbers of all types of mutations — substitutions, deletions, insertions, gene duplications, and more. And in that astronomical number of opportunities, at best a handful of mutations were useful to it.

Parallel Criticisms

Doug Axe’s research on enzymes evolving new protein folds elicits the same pattern of criticism from Rosenhouse. Axe highlights the need for multiple coordinated mutations in the evolution of TEM-1 beta-lactamase, computing some jaw-droppingly small probabilities (on the order of 1 in 10^77). Rosenhouse cites a critic (p. 187), in this case plant biologist Arthur Hunt, who claims Axe got it all wrong by focusing on the wrong strain of the enzyme (a weakened form rather than the wild type). But then Rosenhouse forgoes citing Axe’s response to Hunt. Here’s a relevant portion of Axe’s response: 

In the work described in the 2004 JMB paper [to which Hunt and Rosenhouse were responding], I chose to apply the lowest reasonable standard of function, knowing this would produce the highest reasonable value for P, which in turn provides the most optimistic assessment of the feasibility of evolving new protein folds. Had I used the wild-type level of function as the standard, the result would have been a much lower P value, which would present an even greater challenge for Darwinism. In other words, … the method I used was deliberately generous toward Darwinism.

Now it may seem that I’m just doing what Rosenhouse does, namely, giving my guys the final word. But if I am, it’s not that I’m trying prematurely to end the discussion — it’s just that I’m unaware of any further replies by Miller and Hunt. On the other hand, Rosenhouse, in writing his “state of the art” book on mathematical anti-evolutionism should, presumably, be up on the latest about where the debate stands. Miller’s review of Behe in Nature was back in 2007. And Hunt’s response to Axe occurred on a blog (pandasthumb.org), also back in 2007. Behe responded to Miller right away, in 2007, and Axe’s response appeared in BIO-Complexity in 2011. So if Rosenhouse were fair-minded, he could at least have noted that Behe and Axe had responded to the criticisms he cited. The fact that Rosenhouse didn’t suggests that he has a story to tell and that he will tell it regardless of the facts or evidence.

The Third Way

In closing this post, I note that design proponents are not the only ones questioning and rejecting the Darwinian view that selection acting on single mutational changes can drive the evolutionary process. James Shapiro, a biologist at the University of Chicago, represents a group called The Third Way: Evolution in the Era of Genomics and Epigenomics. A decade ago, Shapiro wrote what essentially amounted to a manifesto for The Third Way: Evolution: A View from the 21st Century (2011). There he argued that organisms do their own “natural genetic engineering,” which is teleological and thoroughly non-Darwinian. Granted, Shapiro is not a fan of intelligent design. But in personal conversation I’ve found him more anti-Darwinian, if that were possible, than my intelligent design colleagues. Specifically, I remarked to him that I thought the Darwinian mechanism offered at least some useful insights. Shapiro responded by saying that Darwin’s effect on biology was wholly negative. This exchange happened in his office during my 2014 visit to the University of Chicago, which was arranged by Leo Kadanoff and described earlier in this series. 

Next, “Conservation of Information — The Idea.”

Editor’s note: This review is cross-posted with permission of the author from BillDembski.com.