Texas Textbooks and Punctuated Equilibrium
In 2009, when the Texas state board of education revised the state science education standards, creationists led by Don McLeroy (then the board chairman and a dentist, now only a dentist) pushed hard to add a standard requiring students to “analyze and evaluate scientific explanations concerning any data of sudden appearance, stasis, and sequential nature of groups in the fossil record.” McLeroy explained this amendment by repeatedly referencing punctuated equilibrium, and listing endless quotations purporting to show that the fossil record is full of sudden appearances and stasis, without much gradual change to be seen.
Jeremy Mohn did yeoman’s work documenting how those quotations were taken out of context and misrepresented, so I won’t rehash that whole episode here. All that anyone really needs to remember about this is that it was this amendment that McLeroy was defending when he famously declared: “I disagree with these experts, somebody’s got to stand up to experts!”
Now, in 2013, as creationist textbook reviewers were combing the textbooks for places to derail accurate science education (as we’ve discussed in previous blog posts), they turned back to that same standard. Ide Trotter, a chemical engineer active with a statewide creationist advocacy group, claimed that the Pearson/Prentice-Hall textbook by Ken Miller and Joe Levine, the nation’s best-selling biology textbook, had a factual error because:
Page 449 SERIOUSLY MISREPRESENTS THE BALANCE BETWEEN GRADUALISM AND SUDDEN APPEARANCE IN THE FOSSIL RECORD. RATHER THAN AS STATED IN PARAGRAPH “Gradualism” AS “sometimes” AND IN PARAGRAPH “ Punctuated Equilibrium” AS “Now and then,” AS THE FOSSIL RECORD IS EXPANDED IT IS BECOMING QUITE CLEAR THAT STASIS FOLLOWED BY SUDDEN APPEARANCE IS THE PREDOMINANT PATTERN.
PARAGRAPH "The Age of the Earth" PRESENTS A VERY OUTDATED VIEW. Even up to the middle of the 20th century the available fossil record made a long drawn out and gradual evolutionary process seen to adequately fit the data. Now abundant data make it clear that evolution appears to occur in short periods of time, geologically speaking. The biggest known evolutionary event, The Cambrian Explosion, took on the order of only 10 million years or less. Following Eldridge and Gould the default understanding has become stasis followed by rapid appearance, Punctuated Equilibrium. That this book has failed to make the move to a 21st century understanding of the fossil record is made clear by statements that no longer are relevant such as an "Earth about 4.5 billion years old-which allows plenty of time for evolution." This can be seen by the elaborate treatment of the development of early Darwinian theory, almost 20 pages, pp 448 to 467, which is certainly an interesting example of how evolutionary science developed. The dated nature of the presentation is further reflected by the weakness of treatment of where evolutionary science is today. The Cambrian explosion is buried in only two paragraphs on page 753. Punctuated Equilibrium is given only two paragraphs on page 549 and these represent either an unbelievable uninformed understanding of the current view of the prevalence of stasis and sudden appearance or a deliberate attempt to avoid letting students know about the challenges that are making the advance of evolutionary theory so exciting today.
(All typos from the original.)
Similar comments were directed at other publishers, but that’s enough creationist text for one blog post, and summarizes the claims publishers have to contend with nicely enough. (I’ll leave aside the issue of the Cambrian for this blog post, except to note that the two topics are deeply entwined in the creationist mind, though it’s not a major feature of the actual punctuated equilibrium literature. I’ll also tactfully not mention that Trotter misspelled Niles Eldredge’s surname.)
The idea that “stasis followed by sudden appearance is the predominant pattern” in the fossil record simply isn’t true, and punctuated equilibrium is hardly “the default view.” A recent review article in Trends in Ecology and Evolution by researchers at the University of Idaho summarized and assessed the state of research on punctuated equilibrium. They found:
a resurgence of interest in PE as paleobiologists and, increasingly, comparative biologists armed with molecular phylogenies, have applied sophisticated statistical models to test quantitatively the major hypotheses of PE. In this review we ask whether these new statistical advances have ‘rescued’ PE from intellectual extinction. We answer this question in the negative. The challenges inherent in elucidating macroevolutionary processes and patterns from paleontological and comparative data are only exacerbated by the muddled historical legacy of PE. Although a number of studies have indeed discussed their findings in light of PE, they have actually addressed a wide variety of conceptual issues; the studies from which we have quoted above exemplify this – each one asks a fundamentally distinct question.
The idea that evolutionary history is dominated by pulses of change as opposed to gradual change is one of the four threads the researchers tease out from the punctuated equilibrium literature, but Trotter and the other creationist reviewers never even consider the other three elements. And the TREE review finds no strong evidence for that particular thread anyway:
PE is tied to a very specific pattern of evolution and a specific temporal frame: stasis over the lifespan of a species (typically millions of years) followed by geologically brief bursts of phenotypic evolution occurring at speciation. Therefore, even robust support for a pattern of pulsed evolution – represented by shifts in trait values along branches that are not accounted for by a model of gradual evolution – may be incompatible with PE if the pulses occur too infrequently for conventional PE theory, which predicts pulses at all (or nearly all) speciation events. In addition, exactly as paleontologists have long recognized that repeated burst–stasis episodes can appear gradualistic if viewed at too coarse a scale, gradualistic evolution with variable rates can appear pulse-like at the same coarse scale. …
(Emphasis added.) The evidence available to us is generally not sufficient to test the different hypotheses, and what evidence exists is mixed.
Instead of trying to place punctuated equilibrium at the center of modern evolution, then, the researchers argue for separating out the concepts, treating them separately, and following the evidence:
multiple processes could be important (and often, probably are) to understanding the accumulation of diversity and disparity through deep time. … Instead of bringing new insight into PE – and thereby rescuing the term from its historical problems – novel developments have demonstrated that the terminology associated with PE can be problematic. … Although PE undoubtedly served as a catalyst in the development of concepts and methods discussed above, we think it is time to move on, and encourage researchers in macroevolution to look forward rather than look back.
The takeaway message? Claims about patterns of stasis and rapid change depend on the time scale we’re looking at, and the time scale that the rocks preserved for us, leaving it difficult or even impossible to distinguish a pattern of gradual evolution from stasis interspersed with rapid evolutionary radiation. Punctuated equilibrium is an interesting idea that inspired some new research, but it’s hardly the center of the discipline of biology. If publishers followed the advice of the Texas review panels, they would be ignoring the actual science.
Research Cited: Matthew W. Pennell, Luke J. Harmon, Josef C. Uyeda (2013) “Is there room for punctuated equilibrium in macroevolution?” Trends in Ecology & Evolution, http://dx.doi.org/10.1016/j.tree.2013.07.004