Friday, July 4, 2014
It’s been a while since I’ve written about Bigfoot, and that’s a shame because he’s pretty fun to write about. As with many things, I like to keep it in a scientific context. That’s why I was pretty stoked to see a recent Sasquatch paper in Proceedings of the Royal Society B. A paper that takes an interesting approach: genetics.
Right off the bat the paper does not assume non-existence, both pointing out that there are numerous reports and sightings yet no bodies or recent fossils. Theories abound about what these animals are, ranging from surviving populations of collateral hominids to unlikely hybrids. As a general rule, modern science shies away from the yeti-finding field, to the point that they make believers feel rejected. Admittedly, believers have point in that science should not accept or reject anything without examining the evidence and testing hypotheses. Pretty much the definition of science, right? So that's what authors Sykes et al. do, take a scientific approach.
The researchers collected a total of 57 Bigfoot hair samples submissions from museum and individual collections. They went about it all officially with a joint press release in May 2012 by Museum of Zoology, Lausanne and the University of Oxford. Then, to eliminate obvious non-hairs, they subjected the samples to macroscopic, microscopic and infrared fluorescence examination. Based on provenance or historic interest, thirty-seven of the samples were selected for genetic analysis. Hairs were first cleaned to remove surface contamination - just consider how many people had handled a sample, so you need to eliminate known human DNA to leave just sample DNA. The meticulously cleaned hair samples were then ground in a buffer to homogenate, incubated with proteinase K, and extracted for PCR amplification. This amplification was of the ribosomal mitrochondrial DNA 12S fragment corresponding to bps 1093-1196 of the human mitrochondrial genome, using a permissive primer combination that allows for a wide range of mammalian DNA. The results were then compared to GenBank accessions for species identification.
Perhaps it is important to point out what the 12S mitochondrial DNA is and how it works. Even within fur-bearing species, there is a large amount of variation in hair appearance that can be identified under the microscope to determine species. But, in the absence of an experienced hair examiner (yes, those exist), a reliable, alternative analysis must be used. This analysis comes in the form of highly conserved mitochondrial DNA regions, these are particular sequences that have been maintained by evolution despite speciation, probably because they are functional. Mitochondrial 12S ribosomal RNA has an amplification size that renders it useful for even problematic and/or degraded samples. Highly conserved primer regions and the high nucleotide species diversity present within the portion of the 12S gene examined allows for identification at least to genus and often species. Studies examining the extent of 12S homology within and between species have shown a high degree of confidence in the test's ability to match species from biological samples, usually hair. This includes primate homologies like the chimpanzee, who shares a 98% homology with the human 12S region, Gorilla (97%) and rhesus macaque (90%). These studies have shown that it is unlikely that a non-human primate hair could be confused with human hair using this system.
Now knowing all of this, back to the results of the Bigfoot study. Despite multiple attempts, seven of the samples yielded no DNA sequences, leaving the researchers with 30 samples. These 30 samples were each matched to a known species. Ten belonged to various bear species, four were cows, four were horse, four were wolves/dogs, two were raccoons, one was a deer, one a Malaysian tapir, one a sheep, one a serow, and one was human (exact match).
There has been quite a few articles in the news about this study, and that’s good because this paper is a nice example of using hard science to test a theory. It is also works towards bridging the gap between two rather disparate groups of people. So kudos to you Sykes et al.
Sykes, B., Mullis, R., Hagenmuller, C., Melton, T., & Sartori, M. (2014). Genetic analysis of hair samples attributed to yeti, bigfoot and other anomalous primates Proceedings of the Royal Society B: Biological Sciences, 281 (1789), 20140161-20140161 DOI: 10.1098/rspb.2014.0161
A nice write-up from Science News "'Bigfoot' samples analyzed in lab"
For more on 12S see an article in Forensic Magazine titled "Easy Species DNA Identification for the Forensic Laboratory Using 12S Mitochondrial DNA"
(images via WhoFortedBlog, NewEngland BioLabs, Nature Reviews Genetic paper DOI:10.1038/nrg1606, respectively)