Niles Eldredge - The Darwin Blogs

The Darwin Blogs – October 9, 2006.

Important News—and an Open Letter to Mr. CD

This past week has been very exciting—and I have important news on two separate fronts:

The Darwin Exhibition: First of all, I am delighted to report that the exhibition Darwin—the show I curated that ran in New York at the American Museum of Natural History from Nov. 19, 2005 until August 20th of this year—is now back up and running at the Franklin Institute in Philadelphia—where it will remain for the rest of this year. I had been saddened to see Darwin close in New York; the last I saw it, it was all carefully crated up and being loaded onto four enormous moving vans. Very poignant!

But what a thrill to see it up in all its glory in Philadelphia! The exhibition has been mounted in a terrific, large space—and my wife Michelle and I were very happy as we renewed our acquaintance with all the wonderful artifacts and specimens—the greatest collection of Darwiniana ever assembled for public display. Over 500,000 visitors saw the exhibition in New York—and advance sales are very promising at the Franklin Institute.

In conjunction with the opening of Darwin at the Franklin Institute, I was happy to share the stage in an informal conversation with Randal Keynes—one of Darwin's great great grandsons. Randal was instrumental in our obtaining the wide and deep assortment of letters, manuscripts, personal effects and specimens that we used to tell the story of Darwin's personal life—and of course his scientific work. I am also pleased to report that Randal has been spearheading the nomination of "Darwin at Downe" as a prospective World Heritage Site. Let's hope that the UNESCO selection committee acts favorably on this important nomination: it would be wonderful to see Down House, Downe village nearby—and a large swathe of neighboring lands—set aside for special attention and protection. What fitting recognition of the power and significance of Darwin's contributions to our intellectual and cultural heritage!

Molecular Evidence for Punctuated Equilibria: On Friday, October 6, the journal Science (along with the British journal Nature, one of the two premier journals in all of science) published an article by British molecular biologist Mark Pagel and his colleagues Chris Venditti and Andrew Meade, entitled "Large Punctuational Contribution of Speciation to Evolutionary Divergence at the Molecular Level" (Science vol. 314, #5796, pp. 119-1210). The paper is a very welcome validation—even vindication—of some of the central claims of "punctuated equilibria" that I first published in 1971—and of course in the paper with Stephen Jay Gould ("Punctuated Equilibria: An Alternative to Phyletic Gradualism") published a year later.

The central empirical observation on which we based the notion of punctuated equilibria is stasis: the observation that most species in the fossil record actually show very little evolutionary change throughout their histories—histories that may be measured in the millions of years. As a corollary, then, evolutionary change between species must be concentrated in relatively much shorter intervals of time—which we predicted would correspond to episodes of speciation—i.e. when a species divides into two (sometimes possibly more) species—usually seen as the origin of a new, daughter species which takes its place alongside the original, ancestral species. It is in the new daughter species where most of the evolutionary change shows up.

Why would evolutionary change be concentrated in speciation events? After all, speciation minimally entails only enough genetically based anatomical or behavioral change to produce reproductive isolation—where the populations that are becoming the new daughter species are no longer able to freely interbreed with members of the parental species. But the fossil record seems to suggest that more is at stake: the adaptive changes that occur in the evolutionary history of lineages mostly occur along with the development of simple reproductive isolation.

A multidisciplinary team of geneticists and paleontologists recently examined the causes of stasis (see Eldredge, N. et al., 2005, The Dynamics of Evolutionary Stasis; downloadable from the "Library of Evolution" on this website). We concluded that species with far-flung distributions are typically integrated into a variety of ecosystems; different populations face somewhat different environmental conditions—including predators, prey species (for animals), temperature, availability of water, etc etc. Each local population, in other words, is adapted to a somewhat different set of environmental conditions than the other populations of the same species living elsewhere. Thus it is unlikely that natural selection can modify an entire species in any one particular direction given the disparate conditions to which the local populations are adapted.

Adaptive evolutionary change is most likely to occur in small populations genetically isolated from other populations—precisely the conditions that arise in speciation. It has become increasingly obvious to paleontologists that speciation events in unrelated lineages tend to be concentrated in relatively brief time intervals—usually following an episode of ecological disruption sufficiently severe to cause the extinction of many species. These so-called "turnovers" happen at many scales: from regional events all the way up through the truly global mass extinctions of the geological past. Environmental change drives many species extinct—but it some cases, in the fragmented habitats that typically develop when environmental change occurs, populations of species can become isolated, leading to the rapid evolution of new species. For example, paleontologist Elisabeth Vrba (who coined the term "turnovers" in the first place) writes of the climate changes in Africa beginning a little over 2.5 million years ago—when a drop in global temperature forced a change from wet tropical woodlands to drier open savannah grasslands in eastern and southern Africa. Many species of antelope and other groups of mammals became extinct—and new species evolved for life on the savannah. Not surprisingly, this turnover event also affected human evolution. It seems likely that, when new ecosystems are essentially being rebuilt after extinction events, the probability that new species, with new adaptations, will survive is much higher than when a newly formed species is forced to compete with its ancestral species in a stable, mature ecosystem.

That's the picture of punctuated equilibria and turnovers developed in the past few decades by paleontologists (though there were forerunners in the nineteenth century—as Darwin well knew but decided to ignore!). Now Pagel et al. have developed a way to test these ideas by analyzing changes in DNA that accrue over time in lineages of closely related species. Paleontology can predict that most evolutionary change takes place at speciation because stasis—evolutionary non-change—is so prevalent in the histories of species in the fossil record. Pagel et al. have now devised a way to measure directly just how much genetic change is concentrated in speciation events.

Their basic idea is that punctuational change predicts that the amount of genetic change is correlated with the number of "nodes" (speciation events) in an evolutionary tree of related species—while gradual evolution ("gradualism") predicts no correlation between amount of genetic change and the number of splitting events. Rather, gradualism predicts that the amount of genetic change is correlated solely with the passage of time. Indeed, this is the assumption underlying the concept of the "molecular clock"—that the timing of evolutionary events can be calculated simply from the amount of genetic change that has accumulated. Very often, the dates calculated on the basis of the "molecular clock" differ from dates derived from the fossil record. One of the implications of the analysis by Pagel et al. is that this assumption is no longer universally and completely valid.

Pagel et al. found that "approximately 22% of substitutional changes at the DNA level can be attributed to punctuational evolution, and the remainder accumulates from background gradual divergence." From their vantage point as molecular biologists/geneticists, 22% is a "large…contribution"—given the pervasive assumption until now of the clock-like nature of the accumulation of genetic change in evolution.

But from my paleontological perspective, happy though I am that a significant amount of genetic change was found to be associated with speciation, my first reaction was "you think 22% is a LARGE amount?" For my assessment as a paleontologist is that far more than 50% of evolutionary change must be correlated with speciation events. Seemingly, I am never satisfied!

But Pagel et al. address this discrepancy—at least indirectly—when they point out that although they found a significant amount of evolutionary change at the DNA level to be correlated with speciation events, they found no evidence for stasis at the molecular level. And they say that this is not surprising, writing that "there need not be any conflict between these two observations [i.e. substantial stasis at the morphological level vs. no stasis at the molecular level—NE] as it is well known that molecular change can occur independently of morphology."

And that is exactly right. Our multidisciplinary "Working Group" (under the auspices of the National Center for Ecological Analysis and Synthesis) grew out of conversations I had with John N. Thompson, an ecological geneticist—and the reigning expert on "co-evolution." John and I wondered how it could be that, at the morphological level, species could remain so essentially unchanged, even for millions of years, while his populations of moths and their host plants seemed—at least in some populations—to be evolving like mad at the molecular level. So stasis—the phenomenon that led us to propose "punctuated equilibria" over 30 years ago now, is—rather deliciously—virtually absent in the molecular data sets used by Pagel et al. to test the implication—the prediction—from punctuated equilibria: that evolutionary change is substantially tied up in speciation events. It's true 22% of the time in DNA substitutions; its true a lot more of the time for actual anatomical change in evolution. I love it!

An Open Letter to Charles Darwin: Readers of previous blogs are by now aware that I have begun exchanging digital letters on this website with a man I now concede to be Charles Darwin. Disappointingly, I have received no further communiqués from Darwin in this otherwise rather momentous week. I can only assume that he has not written because I was not able fully to answer his query in my letter to him on the previous blog—and promised to complete my thoughts sometime later—something I propose to do right now in the hopes that he will be back in touch.

Darwin had written (see Darwin Blog # 33 for a complete transcript of his letter): "Can you explain this to me: how can it be that a scientific theory—however entwined with religious doctrine it may have become in the minds of certain segments of a populace—has become so commonly and routinely encountered in the political arena—and especially in the formal legal system—of your country? Nearly all of this legislative and legal activity seems centered directly around your education system."

And I replied—incompletely—that this phenomenon of creationism appearing over and over again, in several different guises (creationism has "evolved"—from a purely and unabashedly religious injunction against evolution; to "scientific creationism"; and to its latest manifestation as "intelligent design") in our legislatures and courts, has something to do with our founding documents as a free nation with a system of laws based on, but by no means wholly derived from, the British system of justice. I'll now expand on this answer more fully:

October 8, 2006

Dear Mr. Darwin:

My apologies for having taken so long to complete my answer to your recent query.

You are right, of course, when you suggest that the battles over creationism in the United States have been fought not only in the hearts and minds of its individual citizens, nor solely in its churches; and if the battleground is really in our public schools, the most visible manifestation of the ongoing strife is indeed in the legislatures and especially in our local, and especially federal, court systems.

A Canadian colleague of mine once said to me (this was in the 1980s, when I first got involved in combating creationism in the public schools) that he and his friends used to laugh at us for having what struck them as an absurd running battle with fundamentalists and others who were so intent upon removing evolution from the school curriculum. Until, that is, they themselves began to face an upsurge of creationism promoted by the religious right in their own country.

And he said to me, all of a sudden we saw that here in Canada we in fact do not have the same kind of legal protection that can be brought to bear against religiously inspired inroads into the public arena that we have had from our very beginnings here in the United States.

He was referring to our Constitution and its various Amendments—the specific passage occurring as the so-called "Establishment Clause" of the First Amendment (the 10 amendments to the U.S. Constitution is known as the "Bill of Rights"). The Establishment Clause reads: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof."

The time-honored interpretation of the Establishment Clause is that it is intended to protect the free practice of religion—any religion. Federal laws mandating a specific religion would threaten the free practice of all others—and are hence specifically prohibited.

In the current political climate, there is a marked tendency on the part of the "Christian Right" to proclaim this nation as inherently Christian. The New York Times today (October 8, 2006) carried a long article detailing how "faith-based" initiatives—for example, church-run day care centers—are often exempt from the legally mandated oversight that comparable secular institutions are subjected to.

Protestations form the current right-wing Bush administration to the contrary notwithstanding, the assault on Iraq has all the earmarks of the Crusades of nearly 1000 years ago—replete with a sense that Islam is somehow to be construed as an inferior and inherently warlike religion when compared, for example, with Christianity. Yet, with the suspension of many of our rights (as when suspects are subject to "extraordinary rendition"—shipped off to places like Syria where they are tortured; or when wiretaps are obtained without judicial oversight—the list grows daily of such abuses), it comes as no real surprise that the Establishment Clause is also under attack through subterfuge (as when creationism masquerades as "creation science" or "intelligent design"). The call last year for us all to stop saying "Happy Holidays"—a phrase viewed as an overt attack on the Christian religion—to revert to the "Merry Christmas" of the good old days, is an especially inane example—but utterly symptomatic of the attempt officially to recognize the United States as a Christian nation.

Thank God, as it were, and especially our Founding Fathers, for the Establishment Clause. So far, the way to defeat attempts to remove evolution—or have it watered down by teaching it side-by-side with creationism—has simply been to show that all such attempts are religiously inspired. The Religious Right keeps trying to dissociate creationism from any trappings of its religion—but so far they have failed—for there is otherwise no rational motive for injecting the nonsense, nonscience of creationism in our schools.

So that is why, Mr. Darwin, our travails over creationism have taken on such a legalistic tinge. The deeper question: Why is it that creationism is—historically as well as now (Bush has joined Reagan in casting doubt on evolution and calling for both sides of the "issue" to be taught)—so especially prevalent in the United States? That is a subject I shall defer to a later discussion.

This past week, your great great grandson Randal Keynes told an audience at the Franklin Institute in Philadelphia (in conjunction with the re-opening there of the exhibition Darwin devoted to your life and work) that you had once seriously considered moving to the United States as you worked clandestinely on your theory of evolution through natural selection. Mr. Keynes said that you thought that the United States was a more open society, one not ridden by the sort of orthodoxy that had such a grip on the British citizenry—and therefore possibly a more hospitable place for you to develop and eventually to announce your evolutionary ideas.

Could this be true? I can imagine that you very well might have entertained such thoughts (though that evening last week was the first time I had ever heard of them); but I felt compelled to remark to the audience that I very much doubt that you would see things in the same way today. You are here because of your unease—an unease especially engendered by the state of reception of your views (and of all of evolutionary biology as it has developed since you time) in America. We are proud of our recent sweep of the Nobel prizes—ample evidence that we Americans are still first rate in science. But the climate of opinion—especially as expressed by the success of the vocal Christian Right—in the United States today reflects a society in the grip of orthodoxy every bit as narrow as the one you experienced in England in your day.

Enough. I do hope you will take the trouble once again to write me at this digital address.

Sincerely,

Niles Eldredge

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