Intelligent Design Creationists such as Douglas Axe are surprised by this result [Tar Pit Study Shows Complete Absence of Evolutionary Change]. So, apparently, are the authors even though they are evolutionary biologists and they have published this observation before.
How many Sandwalk readers are surprised by this paper?
AbstractThis issue was thoroughly discussed by Stephen Jay Gould in his 2002 book "The Structure of Evolutionary Theory." He began by quoting a paper by Wake, Roth and Wake (1983) where they asked ...
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 piñon-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.
"With natural selection operating in a changing environment as an agent of adaptation, we expect to see changes at the organismal, ultimately physiological and morphological, level. How, though, can we explain the paradoxical situation in which environments change, even dramatically, but organisms do not?"Thus, the problem was well-known thirty years ago. Environmental change often doesn't cause evolutionary change.
Stabilizing selection is not an explanation for stasis as Gould notes on page 878.
... although we all acknowledge stabilizing selection as too important and pervasive a phenomenon to hold no relevance for this issue, a complete explanation of stasis in these conventional terms seems implausible both on empirical grounds, and also by the basic logic of proper scaling.It looks like stasis in the face of environmental change has been a well-established fact for many decades. This should not be a surprise to anyone who studies evolution [The Paradox of Stasis?].
As often emphasized in this chapter, if stasis merely reflects excellent adaptation to environments, then why do we frequently observe such profound stasis during major climatic shifts like ice-age cycles (Cronin, 1985), or through the largest environmental change in a major interval of time (Prothero and Heaton, 1996)?
The premise—that evolution=adaptation and it is driven by environmental change—is obviously wrong as a generalization.
[Photo credit: I took this picture in February 2012 when I visited the tar pits; La Brea Tar Pits.]
Prothero, D.R., Syverson, V.J., Raymond, K.R., Madan, M., Molina, M., Fragomeni, A., DeSantis, S., Sutyagina, A., and Gage, G.L. (2012) Size and shape stasis in late Pleistocene mammals and birds from Rancho La Brea during the Last Glacial–Interglacial cycle. Quaternary Science Reviews 56:1–10. [doi: 10.1016/j.quascirev.2012.08.015]