The world consists of actual humans who were moved to another planet by aliens, during biblical times, hence having an influence on their religion. The planet is terraformed with earth-like conditions, inhabited with Earth creatures. This has given those humans another motive for a second Noah's ark story. However, the aliens' work did not stop at that. The aliens have engaged in genetic engineering. In this world, in particular, they designed humans which could fly. This flight mechanism strong enough to lift a human in the air is an issue of its own, deserving another discussion which I'm not including in this question. The reason I say that, is the obvious set of challenges which may arise. The issue of increased heat loss at the wings, and drag limiting what clothing they can put on is what gives rise to dealing with cold temperatures.

I sought answers through the standard arguments on how animals deal with cold. However, I have found that some of those answers may even give rise to more questions than solutions. Here are few arguments and their challenges:

  1. Body hair / fur: Humans covering themselves with (say) elk fur, still do not protect themselves as well as elks having just another layer of hair on their skin. To make this more convincing, even non-migrating birds can cope with the cold better than humans, despite their MUCH smaller size and an equally thick layer of feathers. Does fur lose some of its effect when ripped-off from the animal and processed to make a coat? Will human "fur" solve the problem?

  2. Protecting the limbs: The elks have long legs and their extremities are not wider than a human leg. The hair is also shorter. Still, they manage to prevent freezing. It is OK to let the extremities function at lower temperatures, but still we have freezing issues. And yes, elks have to stay out throughout the season.

  3. Extremities have no muscles: Penguins have this anatomy: The leg muscles are inside the body. Long tendons connect the muscles with the legs. Still, that does not explain how the tendons, the feet, the bones, let alone the skin, do not freeze. They are exposed and have no cover at all. Human hands have tendons which move the fingers by means of muscles in the lower arm (between the elbow and the hand). Even though we stand on two, the fingers tend to freeze fairly quickly...

  4. Extra layer of fat: Seals have no fur but have a layer of fat for insulation. That being said, little heat escapes. But, that leaves the skin exposed, receiving little heat. How does the skin avoid freezing? And yes, fat people cannot fly...

So, the design would work if we lived in the tropical zone, or the Mediterranean at best. Unless the human body is f*****-up, those people would need to find ways, or to evolve means, to cope with the cold. It is OK to assume they don't fly in very cold weather. I've seen many documents showing people swimming in ice pools, under the ice, military training in cold weather while exposed to the elements, but still, those people cannot stay out throughout the winter and avoid hypothermia and other illnesses. Generating more heat to cope with the cold is not sustainable long-term and heat retention is more important.

  • 9
    $\begingroup$ I've found that wearing clothes does wonders for my cold tolerance, though this is anecdotal evidence at best. $\endgroup$
    – sphennings
    Nov 9, 2017 at 17:55
  • $\begingroup$ You're already taking a pretty big leap by stating that humans can fly. Why not just say that whatever mechanism made humans fly also has the side effect of making them cold tolerance? $\endgroup$
    – sphennings
    Nov 9, 2017 at 17:57
  • $\begingroup$ If they can do all this engineering, why bother starting with humans at all, just make their own creature. $\endgroup$
    – anon
    Nov 9, 2017 at 18:00
  • $\begingroup$ @anon: The alien's plan remains an open question in this world: Some argue the book of Genesis tells the story of alien intervention. Yet, they cannot tell what was their goal. Your comment on altering metabolism is a good start but I don't know how different human metabolism from other non-hibernating mammals (Wolves, elks) in this regard. $\endgroup$ Nov 9, 2017 at 18:10
  • $\begingroup$ @ChristmasSnow a radical change in metabolism means more than simply the difference between hibernation and non hibernation. It can mean the difference between mammals and amphibians in how the process energy $\endgroup$
    – anon
    Nov 9, 2017 at 18:18

4 Answers 4


There is actually real-world precedent for what you want.

Many indigenous Australians have a genetic mutation that helps them cope with a wide range of temperatures, including freezing.

As discussed by Wikipedia here:

The Australian Aborigines are genetically evolved to stand a wide range of environmental temperatures. They were observed to have been able to sleep naked on the ground at night in below freezing conditions in desert conditions where the temperatures easily rose to above 40 degrees Celsius during the day. By the same token, Tasmanian Aborigines would sleep in snow drifts with nothing on apart from an animal skin. According to the April 2017 edition of the National Geographic magazine, it is believed that this ability of Australian Aborigines, is due to a beneficial mutation in the genes which regulates hormones that control body temperature.

Unfortunately, the only directly cited source is an Australian Broadcasting Corporation article titled Genetic mutation helps Aboriginal people survive tough climate, research finds, posted in January 2014 (Internet Archive copy).

Half of Western Australia's Indigenous population has a genetic mutation that has helped them survive the tough central Australian climate for generations, researchers say.

A team of scientist from the University of Cambridge examined data from the 1980s and found half the Aboriginal people studied had varying levels of the hormone thyroxine, which regulates metabolism.

The genetic mutation helps the body alter its temperature in response to fever, scientists say.

"There is a special mechanism that gives a surge of release as the body moves into fever and the changes in Aboriginal [people] have in fact cancelled this trigger that causes the surge of release," said Emeritus Professor Robin Carrell.

"They can meet a situation where they have a higher body temp without having to accelerate the activity of the whole of the body.

I won't pretend to fully understand the exact mechanics, but it looks like if you twiddle the human body's thyroxine production, which has already happened in the real world due to genetic mutations and thus certainly would be possible to do with genetic engineering, you can end up with humans with a much higher degree of resistance to cold. Which in this case is exactly what the doctor ordered.

It's probably worth noting in this context that Tasmania lies at about 42° southern latitude, which in the northern hemisphere is comparable to the border between France and Spain, to northern Japan, or to the northernmost parts of the contiguous United States, or Newfoundland Canada.

  • $\begingroup$ To some extent this may also be a matter of conditioning. The current record holder for arctic swimming distance has been found to experience a dramatic body temperature increase shortly before jumping in. $\endgroup$
    – Perkins
    Nov 15, 2018 at 21:36

Brown fat / non-shivering thermogenesis.

Brown fat is a metabolic organ present in newborns and in some other animals that allows for "wasteful" metabolism: energy that would normally be used by the mitochondrial to make ATP instead is uncoupled from that process, and makes heat.


Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue (or white fat).[1] BAT is found in almost all mammals...

BAT is especially abundant in newborns and in hibernating mammals.[5] It is also present and metabolically active in adult humans,[6][7] but its prevalence decreases as humans age.[8] Its primary function is thermoregulation. In addition to heat produced by shivering muscle, BAT produces heat by non-shivering thermogenesis.


Non-shivering thermogenesis occurs in brown adipose tissue (brown fat)[2] that is present in all eutherians (swine being the only exception currently known).[3] Brown adipose tissue has a unique uncoupling protein (thermogenin, also known as uncoupling protein 1) that allows the uncoupling of protons moving down their mitochondrial gradient from the synthesis of ATP, thus allowing the energy to be dissipated as heat.

There are adults who have a fair bit of brown fat. It can be a fakeout for cancer on PET scans because the brown fat is hungry for sugar like cancer is (cancer also has a wasteful metabolic path).

Your cold people can be loaded up with brown fat which makes them lots of heat. They will need an enormous caloric intake to support this, of course.

ADDENDUM Fat people should be able to fly too!


Why not remove the requirement that humans need to maintain their body temperature?

Cold blooded animals have diverse enzymes that operate in a wide range of temperatures. The genetically modified humans could be altered such that they no longer need to maintain thermal homeostasis.

  • 2
    $\begingroup$ AKA re-engineer their metabolism $\endgroup$
    – anon
    Nov 9, 2017 at 17:59
  • $\begingroup$ For example, lobsters have blue blood because it works better at lower temperatures. $\endgroup$
    – Luke
    Nov 9, 2017 at 18:04

You keep asking, why doesn't it freeze? I understand that you mean ice forming in tissue. Being really cold isn't a problem unless you've got metabolic processes that rely on certain temperature ranges. So, muscles and nerve cells have to be warm if you're going to use them, and you'll have to warm your skin up if it's ever going to heal.

Penguin feet, seal skin, elk legs, they can all get colder than the core body temperature, but they never actually get as cold as their surroundings. It's much easier to maintain a temperature difference of 10-20 degrees than 100 degrees. Barely enough hot blood goes out to the extremities to keep the flesh above freezing. IRL humans die if their core temperature dips by even a few degrees for too long, but your hands and feet can get very cold before you experience lasting damage. I know some people whose hands are always at about room temperature.

Penguin feet sometimes do freeze when they stand on the ice. Their skin recovers from frost bite very well.

Also, it's impossible to freeze while swimming. The water is above the freezing temperature or it would be ice. If you had some enzymes or ions in your blood that kept the freezing point of your flesh slightly bellow that of water, then you'll be fine.

  • $\begingroup$ Salt water may have a lower freezing temperature as demonstrated in this experiment prezi.com/hbsun2nc6z2-/… but I agree with your general comment: The key issue is to retain extremities at above freezing, though not as hot as the core. $\endgroup$ Nov 9, 2017 at 18:26
  • $\begingroup$ Good answer. It's actually warmer in the polar seas than on polar land, so the penguins and seals might nip into the water to keep warm! The sea can only get down to minus 2 centigrade. The land may be at minus 60 C. $\endgroup$
    – DrBob
    Nov 10, 2017 at 18:29

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