Thursday, 8 January 2015

Yetis, Polar Bears and Brown Bears: Things are Seldom What They Seem

In my post, Abominable Snowman: Yetis from The Long Walk to Bear mtDNA of 22 July 2014, I reported:

The new properly-published genetic evidence is from mitochondrial DNA extracted from hair samples. Short sequences in a highly conserved gene from two samples of ‘yeti’ hair, one from Ladakh (golden-brown in colour) and one from Bhutan (reddish-brown), showed a 100% match to DNA recovered from a Pleistocene fossil of Ursus maritimus, the Polar Bear, but not with examples of modern polar bears.

This conclusion* has now been challenged successfully by C.J. Edwards (Oxford) and R. Barnett (Copenhagen). They found a 100% match of two Yeti hair sequences with a modern Polar Bear, not the Pleistocene fossil. However, Edwards and Barnett then go on to suggest that the DNA might have been damaged in the Yeti hair and that since only a single-base change is needed to identify the sequence as fitting Polar Bear, an alternative origin for the hair samples from Ladakh and Bhutan can be proposed: Ursus arctos isabellinus, the Himalayan form of the Brown Bear and long associated with the Yeti myth. The authors conclude:

As the two hair samples tested by Sykes et al. were golden-brown (Ladakh, 25025) and reddish-brown (Bhutan, 25191), and as the most parsimonious explanation of the sequences recovered is that they came from brown bear and exhibit DNA degradation, we would contend that the hair samples are, in fact, from Himalayan brown bears and not from ‘a previously unrecognized bear species, colour variants of U. maritimus, or U. arctos/U. maritimus hybrids’ as claimed. 

Three of the original authors responded:

Although the error is certainly unfortunate, it does not change the conclusion that the sequences recovered from the ‘yeti’ hairs connect to U. maritimus nor does it invalidate any of the possible explanations discussed in the paper. Importantly, for the thrust of the paper as a whole, the conclusion that these Himalayan ‘yeti’ samples were certainly not from a hitherto unknown primate is unaffected…We stressed in the original paper that the true identity of this intriguing animal needs to be refined, preferably by sequence data from fresh tissue samples derived from a living specimen where DNA degradation is no longer a concern

Where would I put my money if I had to choose the most likely source of the Yeti hairs? Brown.

View image |                                                                           Himalayan Brown Bear

*Sykes, BC, Mullis, RA, Hagenmuller, C, Melton TW, Sartori M. 2014. Genetic analysis of hair samples attributed to yeti, bigfoot and other anomalous primates. Proceedings of the Royal Society B 281, 20140161

†Edwards CJ, Barnett R. 2015 Himalayan ‘yeti’ DNA: polar bear or DNA degradation? A comment on ‘Genetic analysis of hair samples attributed to yeti’ by Sykes et al. (2014). Proceedings of the Royal Society B 282: 20141712. 

‡Melton TW, Sartori M, Sykes BC. 2015 Response to Edward and Barnett. Proceedings of the Royal Society B 282: 20142434.