Lessons From Ötzi, the Tyrolean Ice Man. Part III

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There are two reasons why I chose this time to write about Otzi.  The first is that I've been looking for a good excuse to revisit human evolutionary history, particularly that of Europeans, and what it does and doesn't tell us about the "optimal" human diet.  The second is that Otzi's full genome was sequenced and described in a recent issue of Nature Communications (1).  A "genome" is the full complement of genes an organism carries.  So what that means is that researchers have sequenced almost all of his genes. 


I have a background in genetics, but genetic anthropology is complicated and it isn't my field.  Some of what I'll present in coming posts is still vigorously debated in anthropology circles, and I don't know the details of all the arguments.  I'll do my best to present the science as I understand it, and if you happen to be a genetic anthropologist and you have a different perspective, please share it in the comments.

Otzi's Mitochondrial Genome

The first genetic information we have about Otzi predates the recent paper by 18 years.  Mitochondria are the cell's tiny power plants, and they have their own tiny genome that's passed down through the maternal lineage.  In 1994, a German group published the first analysis of his mitochondrial genome, indicating that Otzi is genetically related to present-day Europeans (2).  Later papers described his full mitochondrial genome (3, 4). 

Modern-day people are divided into mitochondrial "haplogroups", which simply indicates relatedness through the maternal lineage.  What these papers found is that Otzi belongs to haplogroup K, a haplotype that's present in about 6 percent of people in Europe and the Near East today.  Haplogroup K originated about 16,000 years ago near the cradle of agriculture in the Middle East, and spread outward from there.  It has been found in the remains of early agricultural populations in the Middle East and Europe (5, 6, 7, 8).

These mitochondrial studies indicate that Otzi was, at least in part, a genetic migrant descended from early agriculturalists in the Middle East, rather than a full descendant of local hunter-gatherer populations in Europe that adopted agriculture over time. 

Otzi's Nuclear Genome

The "nuclear genome" is the complement of genes that's contained in the nucleus, and it represents by far the lion's share of a person's genetic material.  This is what the recent paper reported sequencing (9).  It contains a number of insights:

• Otzi is most closely related to modern-day Sardinians.
• Otzi had several genetic cardiovascular disease risk factors that collectively would have put him at a substantially elevated risk of having a heart attack or stroke.  This may explain his vascular disease, at least in part.
• Otzi probably had Lyme disease, a chronic and serious bacterial infection transmitted by ticks.
• Otzi probably had brown eyes.
• Otzi was lactose intolerant.
• "...Otzi carried a large genomic region known as the ‘Y chromosome’, which significantly increases the risk of traipsing about in the a*se-end of nowhere with very little protective clothing, and getting shot by arrows" (10)

In addition, his Y chromosome indicated that his paternal lineage (haplogroup G) also has roots in early agricultural populations in the Middle East.  This is the same lineage that has been found in other early agricultural remains in Europe (11).  This is consistent with his mitochondrial genome and indicates that he descended in large part from early adopters of agriculture in the Middle East.

Why do We Care about Otzi's Genome?

I'm going to begin to answer that question with a question.  What was a man of Middle Eastern agriculturalist descent doing on the border of Italy and Austria 5,300 years ago?  And what were genes originating from early Middle Eastern agriculturalists doing in many other parts of Europe as early as 8,000 years ago (12)?  These findings, among many others, suggest that agricultural populations from the Middle East not only brought their subsistence strategy to Europe, they also brought their genes. 

Researchers have found that Paleolithic humans and neanderthals in Europe had a diet that was heavily focused on meat (13, 14), and this has been used to suggest that modern-day people of European descent should eat a meat-heavy, low carbohydrate diet to mimic their own ancestral dietary pattern.  But this makes a big assumption: that those Paleolithic meat eaters were the ancestors of modern-day Europeans. If instead, modern Europeans descend from Middle Eastern agriculturalists who originally came from Africa, that means they were never hunter-gatherers in Europe and therefore never ate a diet focused on meat and fat-rich large temperate game.  If they descended from Middle Eastern agriculturalists who ate a high-carbohydrate grain-based diet for some 10,000 years, this may lead to different conclusions about the ancestral European diet.

In future posts, I'll explore what research has uncovered about European ancestry, human evolution since the development of agriculture, and what that means for the human dietary niche.