Sunday 29 May 2016

Debunking the Yeti

When I was much younger my mind was so open you could have driven a bus through it. Not that I was gullible (I always knew that was a word in the dictionary), but when it came to strange phenomena you could sign me up for every cranky belief going. UFO's and the conspiracies surrounding them were a favourite, but everything else - Loch Ness Monster, ghoulies and ghosties, supernaturally things, I was game for the lot. Now (much) older and wiser, a part of me is gratified whenever long-standing mysteries are debunked and sensible, scientific explanations are offered. And so Channel 4's Yeti: Myth, Man or Beast? with former kids' naturalist, Mark Evans ticked my boxes because, beyond all reasonable doubt, it appears the myth of the abominable snowman was finally, properly been put to bed.

We know the stories and the photos of suspect-looking footprints, and the folklore of Himalayan people. There are also the slightly suspect artefacts of fur, bones, and preserved body parts Tibetan and Nepalese villagers have waved in front of Western cameras for decades. So clearly there is something going on. The mythology of the Yeti is based on something, but what? Mark advanced two hypotheses: that a species of Himalayan bear is the not-so-fantastical basis of many sightings for mountain climbers and local people, or that there is a prehistoric species of human rattling around the roof of the world. Which is it to be? Well, a bit of both.

Much of the programme is spent driving to remote villages, wallowing in breathtaking panoramas, interrogating Tibetans about their local legends, and hanging around labs explaining DNA analysis. For added padding, Mark meets the celebrated mountaineer Reinhold Messner, who happened to have a brush with our elusive friend on an expedition 30 years ago. Having done a great deal of research, he came to conclusion his Yeti could be a hitherto undiscovered species of bear. Au contraire thinks Steve Berry, another professional climber. Presenting a photograph of a set of footprints in the snow, he was adamant only a bipedal creature could have produced them - though when Mark asks a villager, he straight out says they were snow leopard tracks. Darn the cats!

Getting to the nitty gritty, we get back DNA results for fur, bone, and a bit of a dessicated paw and, alas, genetics say no. The Yeti relics were either lowland black bears or highland brown bears. No new species of human then. And yet the alternative hypothesis isn't entirely dead. In a bit of a left field twist, Mark makes mention of recent findings in Denisova cave in southern Siberia. Between 2000 and 2014 archaeologists unearthed fossils pointing to a new species of prehistoric human, who apparently lived alongside Neanderthals and overlapped with modern humans. Mark hypothesised that tales of the Yeti might be folk memory stretching back to these encounters. This begs the obvious question: if that's the case, then why are the legends confined to the Himalaya and not the surrounding lowlands?

In previous analysis of Denisovan fossil DNA, Mark argued that they shared a specific mutation with modern humans living in the highlands: the EPAS1 gene. He explains how non-Himalayans adapt to altitude my producing more red blood cells to carry oxygen throughout the body. However, over a long period this can lead to blood becoming more viscous and result in a number of potentially serious health problems. EPAS1 prevents blood from coagulating at altitude, which allows modern day Himalayans to live without any ill-effects. Mark suggests that this mutation could have been passed into the local population back in the dim and distant through interbreeding with Denisovans, and explains why the legends are particular to Himalayan peoples. This isn't entirely fanciful: there is evidence our ancestors did with Neanderthals. Taking DNA samples from Tibetan volunteers from a previous programme to a Californian lab, Mark was keen to pin down the date when such interbreeding could have taken place - and the result was stunning. The date range was between 40,000 and 7,000 years ago. Amazing.

Case closed then? Bears are responsible for contemporary sightings, and the interaction/interbreeding between our ancestors and Denisovans underpin the mythology. Seems pretty airtight. Yes, but one problem with Mark's "science bit". According to the work underpinning the identification of the EPAS1 gene, its emergence is far more recent in time. 3,000 years to be exact, and it's an independent evolutionary adaptation to a previously unhealthy environment - not the result of interbreeding. That the Denisovans had this too shouldn't be a surprise - nature is littered with examples of convergent and coincident evolution. For instance, combination of different genes had the same effects in the Andean and Ethiopian highlands too without the need of an exotic intervention from another species of human.

While systematic genetic analysis of these populations are ongoing, it's fair to conclude that bigfoot is dead, and has been for tens of thousands of years. Another mystery has been peeled back, and once more what was previously strange phenomena is something interesting but entirely explicable. As unreason spreads its wings and infects too many people with magical thinking, conspiratorial nonsense, and a desire to believe the weird and fantastical, Mark and Channel Four deserve praise for reminding its audience that we have the wherewithal to explain the world without the need for modern day pixies.


Anonymous said...

I dunno. Remember that the giant squid and the panda were mythological animals until fairly recently (20th century for the latter, 19th for the former). Proving that supposed yeti 'relics' are from other animals doesn't disprove the existence of the yeti itself. All that can be said is that those relics are from known animals. I've no opinion on the yeti, but closing the book based on the viewing of this programme is premature to say the least. (There's also a considerable degree of cognitive dissonance in using the DNA of human relatives who were unknown to science until a few years ago -- and only identified by the discovery of three teeth alone -- to argue for the non-existence of another human relative!)

Unknown said...

Exactly, case not closed. EVERY "old school" anthropologist would have argued - just 12 years ago - that there are no more archaic humans to be found from the last 40,000 years. Now we have new hominins in every corner of Eurasia: the Denisovans, Flores Man, Red Deer Cave people. No doubt they will find even more. The human family tree gets bigger and bigger, we now know that we interbred with Neanderthals and Denisovans, Denisovans with a yet unknown even more archaic population and modern sub-Saharan Africans with a yet unknown archaic human that survived at least until 30,000 years ago (we now know that from DNA studies of modern African populations). Perhaps all of these humans survived into the Holocene and are the reasons for the origin of "yeti myths". Well, I have no doubt considerung the relatively low environmental impact of modern humans due to their low population densities in most parts of the world until antiquity or even later.

Unknown said...

and one more point: on EPAS1 you cite a study from 2010, the Denisovan study is from three years later, 2014.
And here is the decisive bit about the "science bit", which is not covered by the 2010 study:
"Re-sequencing the region around EPAS1 in 40 Tibetan and 40 Han individuals, we find that this gene has a highly unusual haplotype structure that can only be convincingly explained by introgression of DNA from Denisovan or Denisovan-related individuals into humans. Scanning a larger set of worldwide populations, we find that the selected haplotype is only found in Denisovans and in Tibetans, and at very low frequency among Han Chinese."
That modern human indeed interbred with Denisovans has been shown on several occassions, last time this year, see:
You see, the story is more complex than a 1 hour Channel 4 docu..;-)

Eliza_Mariah said...

Poor old Yeti. When I was a kid we had a book in the house called Mysteries of the Unexplained. It made no attempt to explain the mysteries. I loved it, but as a result of reading it, I also spent years being terrified of spontaneous human combustion. I still have a fondness for documentaries about Bigfoot and other cryptozoids. I find them most fascinating as cultural phenomenons.