New information has emerged to show that a prediction of neo-Darwinism has been falsified. Everyone knows that animals adapt to their environments. The surge of interest in climate change has stimulated research into morphological change in Galapagos finches, "Siberian warblers, English sparrows, cuckoos, cowbirds, red-winged blackbirds, and many others." The message coming through is that the sizes and shapes of animals can change quickly in response to environmental constraints. These findings have been used as fundamental evidence to support mainstream thinking about organic evolution. As explained by Prothero et al.:
"The classic neontological model of gradualistic evolution argues that organisms are sensitive to small environmental changes, and readily adapt to such changes through transformations of body size or morphology. Such is the tradition of a century of research on the evolution of fruit flies, lab rats, and many other animals, as well as natural examples like the small-scale adaptations of Galapagos finches to drought and other local environmental stresses."
The Page Museum has over 1 million fossil specimens (source here)
Donald Prothero was a student at the American Museum of Natural History when Niles Eldredge and Stephen Jay Gould proposed the "punctuated equilibrium" hypothesis.
"The "punctuated equilibrium" paper is a masterpiece of writing and incisive thinking, which poses a number of interesting issues. The first part is a general discourse on the philosophy of science, which argues that all scientists are products of their time and culture and tend to see what they expect to see. In this context, Darwin led paleontologists to expect phyletic gradualism, which they vainly tried to document for over a century before the allopatric speciation model came along. Then Eldredge and Gould introduced the details of the allopatric model, described punctuated equilibrium, and give examples from their own research (phacopid trilobites from Eldredge, Bahamian land snails from Gould). [. . .]
Many paleontologists came forward and pointed out that the geological literature was one vast monument to stasis, with relatively few cases where anyone had observed gradual evolution. If species didn't appear suddenly in the fossil record and remain relatively unchanged, then biostratigraphy would never work - and yet almost two centuries of successful biostratigraphic correlations was evidence of just this kind of pattern. As Gould put it, it was the "dirty little secret" hidden in the paleontological closet. Most paleontologists were trained to focus on gradual evolution as the only pattern of interest, and ignored stasis as "not evolutionary change" and therefore uninteresting, to be overlooked or minimized. Once Eldredge and Gould had pointed out that stasis was equally important ("stasis is data" in Gould's words), paleontologists all over the world saw that stasis was the general pattern, and that gradualism was rare - and that is still the consensus 40 years later." (source here)
Prothero went on to study for a PhD, which he completed in 1981. This research developed a familiarity with the abundant and well preserved fossil mammals of the Big Badlands of the High Plains. After careful analysis, it became clear that every mammalian lineage showed stasis. He found that stasis persisted through a time of major climatic change (the Eocene-Oligocene transition). Intrigued, Prothero "began to re-examine the uncritical acceptance of the notion that fossil mammals track environmental changes". He looked at the middle-late Eocene climate upheaval, the Eocene-Oligocene transition, the great expansion of modern grasslands dated at 7.5 million years ago, and the Pleistocene ice ages. The evidence for stasis was impressive. Ice age stasis was recognised, but widely interpreted in terms of animals migrating to where comfortable climates prevailed. This thesis needed more attention.
"I had a bunch of excellent students in my paleontology classes at both Occidental and Caltech, and several wanted to do research with me. I was at a loss over how to supervise so many undergraduates with limited backgrounds, until I realized that we could do a group of related projects practically in our back yard: the Page Museum at La Brea tar pits in Los Angeles. I equipped each one of them with calipers and gave them a measuring protocol, and got them access to the La Brea fossils through the collections managers. Then they each measured a different Ice Age mammal or bird, collecting data on hundreds of bones from all the tar pits with good radiocarbon dates: saber-toothed cats, dire wolves, giant lions, bison, horses, camels, ground sloths, plus the five most common birds: golden and bald eagles, condors, caracaras, and turkeys." (source here)
The studies of individual groups have been published as separate papers, but an overview paper has now appeared. The tarpits allow a sampling of fossil mammals and birds from an interglacial, through a glacial and into the next interglacial. The fauna experienced a major climatic transition and Prothero's goal was to test out the relevance of Bergman's rule (where more cold-adapted species or subspecies tend to have larger body sizes to conserve body heat), and Allen's rule (where more cold-adapted species or subspecies tend to have shorter and more robust limbs and other appendages (such as ears) compared to those of warmer climates). This is what he and his students found:
"After six years of work and publication, the conclusion is clear: none of the common Ice Age mammals and birds responded to any of the climate changes at La Brea in the last 35,000 years, even though the region went from dry chaparral to snowy pinon-juniper forests during the peak glacial 20,000 years ago, and then back to the modern chaparral again." (source here)
So Prothero's research has provided solid evidence for stasis and against gradualism in response to environmental change. He is to be commended for following the evidence and not trying to force-fit it into a Darwinian mould. However, he needs to think again about comments like this:
"In four of the biggest climatic-vegetational events of the last 50 million years, the mammals and birds show no noticeable change in response to changing climates. No matter how many presentations I give where I show these data, no one (including myself) has a good explanation yet for such widespread stasis despite the obvious selective pressures of changing climate. Rather than answers, we have more questions - and that's a good thing! Science advances when we discover what we don't know, or we discover that simple answers we'd been following for years no longer work." (source here)
"Such stasis, along with the examples documented from nearly all other Pleistocene mammals and birds, argues that organisms are not as responsive to environmental change as classical neo-Darwinian theory predicts." (Last sentence of the paper)
It is not fair to say that "no one has a good explanation" for the observed stasis. This blog has addressed these issues repeatedly. Stasis is not an oddity in the fossil record - it is pervasive. There are scientists who have concluded there are limits to variation, and that speciation tends to reduce the ability of organisms to respond to their environments. This approach considers that many speciation events result in genetic loss, restricting phenotypic plasticity. This approach has the merit of explaining the observational data - but anyone proposing that there are limits to variation faces a grilling from evolutionists. It's not a case of rejecting their science - it's a case of rejecting their metaphysics.
Size and shape stasis in late Pleistocene mammals and birds from Rancho La Brea during the Last Glacial-Interglacial cycle
Donald R. Prothero, Valerie J. Syverson, Kristina R. Raymond, Meena Madan, Sarah Molina, Ashley Fragomeni, Sylvana DeSantis, Anastasiya Sutyagina, Gina L. Gage
Quaternary Science Reviews, Volume 56, 21 November 2012, Pages 1-10 | http://dx.doi.org/10.1016/j.quascirev.2012.08.015
Abstract: Conventional neo-Darwinian theory views organisms as infinitely sensitive and responsive to their environments, and considers them able to readily change size or shape when they adapt to selective pressures. Yet since 1863 it has been well known that Pleistocene animals and plants do not show much morphological change or speciation in response to the glacial-interglacial climate cycles. We tested this hypothesis with all of the common birds (condors, golden and bald eagles, turkeys, caracaras) and mammals (dire wolves, saber-toothed cats, giant lions, horses, camels, bison, and ground sloths) from Rancho La Brea tar pits in Los Angeles, California, which preserves large samples of many bones from many well-dated pits spanning the 35,000 years of the Last Glacial-Interglacial cycle. Pollen evidence showed the climate changed from chaparral/oaks 35,000 years ago to snowy pinon-juniper forests at the peak glacial 20,000 years ago, then back to the modern chaparral since the glacial-interglacial transition. Based on Bergmann's rule, we would expect peak glacial specimens to have larger body sizes, and based on Allen's rule, peak glacial samples should have shorter and more robust limbs. Yet statistical analysis (ANOVA for parametric samples; Kruskal-Wallis test for non-parametric samples) showed that none of the Pleistocene pit samples is statistically distinct from the rest, indicating complete stasis from 35 ka to 9 ka. The sole exception was the Pit 13 sample of dire wolves (16 ka), which was significantly smaller than the rest, but this did not occur in response to climate change. We also performed a time series analysis of the pit samples. None showed directional change; all were either static or showed a random walk. Thus, the data show that birds and mammals at Rancho La Brea show complete stasis and were unresponsive to the major climate change that occurred at 20 ka, consistent with other studies of Pleistocene animals and plants. Most explanations for such stasis (stabilizing selection, canalization) fail in this setting where climate is changing. One possible explanation is that most large birds and mammals are very broadly adapted and relatively insensitive to changes in their environments, although even the small mammals of the Pleistocene show stasis during climate change, too.
Prothero, D.R. Darwin's Legacy, eSkeptic (15 February 2012)
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