The polar bear (Ursus maritimus) exhibits numerous adaptations to cold environments, fur, foot pads, head shape, exclusively carnivorous diet, heightened sense of smell, etc. Their close relationship to the brown bear (Ursus arctos) has long been recognised. Fertile hybrids are well-documented in captivity and there are rare examples of hybrids in the wild - the most recent being in 2006. Interbreeding, however, has not outweighed other taxonomic criteria, although it has been a factor in moving the polar bear from the genus Thalarctos back to the genus Ursus. "With their distinctly different morphology, metabolism, and social and feeding behaviors, the polar and brown bears are classified as separate species." Interestingly, a cluster of brown bears (known as ABC bears) have been found with close genetic links to polar bears.
"Recent genetic studies have shown that polar bears evolved from within brown bears, and that a genetically unique clade of brown bear populations that live exclusively on the Admiralty, Baranof, and Chichagof (ABC) islands of southeastern Alaska's Alexander Archipelago are more closely related to polar bears than to other brown bears."
The cold and dry conditions where this ancient polar bear jaw and canine were fossilized kept DNA within well preserved. (Credit: O. Wiig/University of Oslo's Natural History Museum, source here)
Speciation, then, has occurred, but when? how? and over what timescale? The opportunity to constrain the answers to these questions has come with the discovery of a jawbone with diagnostic polar bear traits from a site in Norway estimated to be 130-110 ky old. This makes it the most ancient sub-fossil yet to be recovered. Approximately 0.1 g of bone powder was used to generate a "complete, high-quality mt genome" using next-generation sequencing technology.
"The organization and length of the genome is comparable to that of extant bears, showing clear sequence similarity to both ABC bears and modern polar bears."
Using these data, phylogenetic analyses have been performed to probe relationships between the fossil bear (the Poolepynten specimen), modern-day polar bears, ABC bears and the modern brown bear variants.
"The phylogenetic results clearly demonstrate, with high support, the close relationship of the subfossil specimen to modern polar bear. Intriguingly, however, this ancient polar bear, which exhibits a very short branch length, lies almost directly at the branching point between polar bear and the genetically unique clade of ABC brown bears. Thus, both cladistically and anagenetically, this ancient specimen existed very close to the most recent common ancestor of polar bears and brown bears."
It is known that the diet of modern polar bears is dominated by ringed seals and bearded seals. Using the stable isotopes of carbon and nitrogen, it is possible to assess whether animal teeth (modern or sub-fossil) have a marine or a terrestrial signature.
"The stable isotope values for the ancient tooth [. . .] were within the range found from extant polar bear teeth and other tissues and were reflective of marine feeding. Importantly, these isotope values are distinct from those found in Late Pleistocene brown bears, including from the ABC brown bear lineage, as well as present-day coastal Alaskan brown bears. Thus, our results clearly demonstrate that the jaw is from an individual that had a feeding ecology similar to present-day polar bears, at the top of the Arctic marine food chain."
Using a molecular clock approach, the divergence time for the split between ABC bears and polar bears was estimated to be 152 ky. A further estimate was made of the emergence of the crown group of polar bears:
"Even more surprising, the age of the modern polar bear crown group (the clade containing the last common ancestor of all extant members) is estimated to be less than 45 ky, slightly older than the age of the ABC bears, a date that is also found with the expanded dataset of control-region sequence fragments. These estimates suggest a very recent and rapid expansion of modern polar bear populations throughout the Arctic since the Late Pleistocene, perhaps following a climate-related population bottleneck, although data from more modern and Holocene polar bear specimens will be required to establish this."
The authors conclude that speciation was rapid, consistent with the punctuated equilibrium (PE) model proposed to explain persistent patterns in the fossil record.
"The stable isotope data, phylogenetic analysis, and the geological and molecular age estimates of the Poolepynten specimen indicate that ancient polar bears adapted extremely rapidly both morphologically and physiologically to their current and unique ecology within only 10-30 ky following their split from a brown bear precursor and, subsequently, within the course of ~100 ky, spread to the full perimeter of the polar basin. As such, the polar bear is an excellent example of evolutionary opportunism within a widespread mammalian lineage. Moreover, the extreme proximity of the Poolepynten specimen to the polar bear ancestor provides a unique case of a morphologically and molecularly validated fossil link between living mammal species."
This research raises important questions for advocates of Darwinism. The PE model has been interpreted by them as a broad brush perspective. Consequently, the fossil record is considered too coarse to pick out the gradual transformation they insist must have occurred (because gradualism is the 'only way' to build complexity and achieve adaptation). However, this polar bear study shows that the timescales for change are too short to permit a viable gradualist explanation. This research shows the PE framework (of abrupt appearance followed by stasis) is realistic. Evolutionary theory must address issues like this and Darwinists should cease their confident rhetoric about the sufficiency of the mechanisms of mutations and natural selection.
Furthermore, Darwinists should realise that mere evidences of speciation are not the same as evidences for their theory. Polar bears display sophisticated adaptations, and if they are not gradualist phenomena, how can they be explained? If biological information is not acquired gradually, where does it come from? The ID perspective on this draws on numerous indicators of pre-existing information (for example, it is now widely recognised that much genetic information and associated regulative systems preceded the Cambrian Explosion). From this perspective, rapid speciation is possible because pre-existing information can be restructured and re-expressed in novel ways. The scientific challenge is to determine the mechanisms responsible for this type of information-rich speciation.
By contrast, Darwinism explains only information-neutral (finch beaks and peppered moths) or information-degradation (antibiotic resistance) scenarios. For confusing these various types of biological transformations, Darwinism's influence on biology has been unhealthy and scientific progress has been inhibited.
Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear
Charlotte Lindqvist, Stephan C. Schuster, Yazhou Sun, Sandra L. Talbot, Ji Qi, Aakrosh Ratan, Lynn P. Tomsho, Lindsay Kasson, Eve Zeyl, Jon Aars, Webb Miller, Olafur Ingolfsson, Lutz Bachmann and Oystein Wiig.
Proceedings of the National Academies of Science, USA, March 16, 2010 vol. 107 no. 11 5053-5057 | doi: 10.1073/pnas.0914266107
Abstract: The polar bear has become the flagship species in the climate-change discussion. However, little is known about how past climate impacted its evolution and persistence, given an extremely poor fossil record. Although it is undisputed from analyses of mitochondrial (mt) DNA that polar bears constitute a lineage within the genetic diversity of brown bears, timing estimates of their divergence have differed considerably. Using next-generation sequencing technology, we have generated a complete, high-quality mt genome from a stratigraphically validated 130,000- to 110,000-year-old polar bear jawbone. In addition, six mt genomes were generated of extant polar bears from Alaska and brown bears from the Admiralty and Baranof islands of the Alexander Archipelago of southeastern Alaska and Kodiak Island. We show that the phylogenetic position of the ancient polar bear lies almost directly at the branching point between polar bears and brown bears, elucidating a unique morphologically and molecularly documented fossil link between living mammal species. Molecular dating and stable isotope analyses also show that by very early in their evolutionary history, polar bears were already inhabitants of the Artic sea ice and had adapted very rapidly to their current and unique ecology at the top of the Arctic marine food chain. As such, polar bears provide an excellent example of evolutionary opportunism within a widespread mammalian lineage.
Kaplan, M., Ancient polar-bear fossil yields genome, Nature News, online 1 March 2010 | doi:10.1038/news.2010.99
Tyler, D.J. Unexpected genome complexity in the starlet sea anemone, ARN Literature blog (11 July 2007)
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