Thermal geography of ancestry
Summary
Vasoconstriction of blood vessels cuts off circulation to the extremities during acute cold exposure, conserving heat to maintain vital organ functions in the torso and reducing risk of hypothermia.
However, reduced blood flow in the fingers impairs dexterity and interferes with manipulating the tools necessary for hunting & fishing.
Ancient selection pressures may explain a counterintuitive biological phenomenon that rewarms fingers during acute cold exposure, allowing some populations from Northern climates the capacity to hunt & fish during winter.
Emigration requires adaptation
My ancient ancestors were from the North Sea, where the winters are long and cold. To hear my Grammy tell it, our people escaped religious persecution by fleeing England in favor of Leiden, Netherlands. Once there, they raised money so they could purchase two vessels -- the Mayflower and the Speedwell -- to make passage to the New World.
They were aiming for Virginia, but never made it that far. The Speedwell leaked so badly that they had to delay their trans-Atlantic voyage by more than a month. When they finally set sail, they left the leaking Speedwell behind, packed additional passengers into the already overcrowded Mayflower, and by the time they reached Massachusetts, it was November of 1620.
In other words, my ancient ancestors were cold, and half of them died before the first anniversary of their voyage.
Thermal comfort could kill me
Back in 2017, Scott Carney delivered a TEDx talk in which he described how a cold-acclimated Native American named Samoset saved the starving Pilgrims by teaching them to farm, fish, and hunt in the strange environment of the New World.
According to my Grammy, those Pilgrims were my people. If someone had offered them central heating, you can better believe they would have taken it. To them, escaping the cold meant survival.
The irony is that the comfort my ancestors never had could become the cause of my premature death. Having survived centuries of extreme cold, my ancestors became genetically adapted to acute cold exposure, and their cold genes have been passed down to me. Should I seek the same thermal comfort that was denied them, my body would be forced to manage under conditions for which it was not well acclimated.
Metabolic syndrome, and disorders like Type 2 diabetes and Alzheimer's, would be the likely outcome (de la Monte 2009).
Hunting in the cold requires blood flow to the fingers
My last name Seager means harpoon. The "Sea-" part, in my case, means the North Sea between the British Isles and Scandinavia. The "-ger" part is less obvious. In Middle English, a "gar" is a spear -- a long, pointed weapon. So a Sea-Gar is an ocean spear, or a harpoon.
In other words, my ancient ancestors were likely cold water hunters.
By contrast, modern thermal comfort is a fairly recent condition in my family. Even my Mother experienced regular cold exposure as a child. She was one of six kids raised in southern Maine, where she and her sister became champion swimmers by training in the cold waters of the Gulf of Maine.
But it wasn't like my Mom ever encouraged any of her three kids to pursue cold acclimation. By the time I was born, the comparative affluence of the 1960's meant populations in the United States rarely suffered the hardship of cold exposure.
By then, modern studies of human cold response sought out the remote populations still living above the Arctic circle. And the scientists who traveled there discovered remarkable metabolic adaptations to extremely cold conditions. For example, a group of six men living in the Norwegian mountains who voluntarily subjected themselves to living in the cold found that after six weeks, they had developed sufficient capacity for thermogenesis to distinguish themselves metabolically from a control group that was not cold acclimated (Scholander et al. 1958). Similar results were obtained from the Lapp people of northern Finland two years later (Andersen et al. 1960).
Nonetheless, given that extreme cold exposure results in vasoconstriction -- i.e., shutting off blood flow to the extremities to conserve body heat -- the evolutionary question relevant to my ancient ancestors is, "How did the cold weather hunters manage their weapons under the kind of extreme cold conditions that would prohibit fine motor dexterity?"
The answer is something called the "Hunter's Response", and it describes a remarkable phenomenon in which the body will rewarm limbs and fingers by temporarily returning blood flow during acute cold exposure -- presumably so that a hunter can maintain the necessary dexterity to manipulate weapons and tools (Daanen at al. 1997).
Inuit hunters can raise the temperature in the skin of their hands from near freezing to fifty degrees in a matter of minutes; for most people it takes much longer. - Dr. Sharon Moalem, in 'Survival of the Sickest' 2007, p36).
Modern-day cold acclimation
The evolutionary utility of the Hunter's Response is the kind of thing that seems obvious only after it is described.
According to Professor of Physiology Hein Daanen, of Vrije Universiteit Amsterdam, the mechanism of the Hunter's Response is called "cold-induced vasodilation" (2003). In cold-acclimated individuals, a seemingly paradoxical vasodilation can occur about 5-10 minutes after the onset of cold exposure. For example, an enthusiastic ice bather from southern California recently wrote to me to describe "such a strange feeling…" he had during an extended session in his ice bath. He wrote:
"After four minutes I was cold. After six minutes I was tingly. After seven minutes and beyond, it was as if my whole body felt warm and I could sit in the ice bath for an hour."
I doubt his warm feeling would have lasted that long. According to Daanen, at longer exposure times when hypothermia becomes a risk, the body somehow knows to prevent vasodilation, conserving all remaining warmth for the preservation of internal organs. Nonetheless, the experience of our southern California customer illustrates how deliberate cold exposure can help put us back in touch with our ancestral roots.
What's even more remarkable is that researchers studying how to train human subjects for enhanced Hunter's Response recently discovered that thermal contrast therapy works better than deliberate cold exposure alone. According to Ciuha et al. (2012) "whole-body heat acclimation increased finger vasodilatory response during cold-water immersion, and enhanced the rewarming rate of the hand, thus potentially contributing to improved local cold tolerance."
That means that the ancient tradition of ice bath and sauna, popular among polar peoples like Finns and Russians, may have been integral in training their bodies to survive during long, dark winters of hunting, ice fishing, or whaling.
The risks of thermal comfort
My Mother hasn't been swimming in the cold in decades. When I was very little, and she would take us to the beach, I remember the times when she would come into the water with me to teach me to swim -- but those days were fifty years ago. After my sisters and I mastered the basic strokes, she was content to supervise us from the shore.
Although she was once an athlete, my sense is that she never developed a self-identity as such. My memory of her from when I was a child is that she bounced from one calorie-counting diet to another, never making any progress on any of them, feeling overweight and living in constant fear of high cholesterol. Back then, regard for evolutionary origins wasn't a thing people talked about, and my Mother was convinced that animal fats, red meat, and dairy would be the death of her.
The consequences for her health have been devastating.
About the Author
Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.
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