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Humans Are a Tropical Species and Not Well-Adapted to Cold Climates

Humans are a tropical species. And, newer anthropological research suggests that we have evolved in tropical forests, specifically. The tropical human nature is not hard to spot – if we ever give it thought! However, many are not aware of our species’ natural habitat, nor of the implications for health, culture, and actually, all spheres of our lives.

Humans are physically not well-adapted to face the challenges of cold climates, and neither do we experience our best health or access our natural diet outside the tropics.

Humans are not well-adapted to cold climates

Animals and plants that have evolved in cold climates can survive winter, but humans can not! The human body would die very quickly outside without our very (!) intelligent cultural adaptations like warm clothing. Unlike well-adapted animals, a naked human would freeze before he starved. And even with clothing, we couldn’t survive the night without warming fires or inside heating.

Insufficient vitamin D production in cold regions is another sign of our tropical ancestry: The need for external vitamin D sources (supplements or vitamin D3-rich animal-based foods) only arises in colder, sun-poor regions.

Humans do not have evolved major cold adaptations like animals

Freezing temperatures and cold weather are generally hard on organisms, even on species with extensive cold adaptations. Those adaptations are usually costly, meaning energy-intensive, but they pay out as they are the prerequisite for survival.

The adaptive characteristics of animals are often a combination of different morphological, physiological, or behavioral traits, i.e., fur and extra fat for insulation, hibernation, specialized foraging skills, etc. Adaptations are traits that have evolved because they increase the fitness (survival and reproduction) of a species rather than by chance (genetic drift).

Thermal adaptations in cold-indigenous people:

Humans have not evolved such extensive biological adaptation to cold environments. This is even true for those populations living in temperate and arctic climates. However, cold-indigenous people have a few traits that seem to have changed due to selection pressure in cold regions:

  • Increased shivering (metabolic heat production) and vasodilation responses (source)
  • Facilitated Vitamin D production trough light (source)
  • Increased lactose tolerance, which enabled the digestion of the available foods in cold habitats
  • The shape of parts of the respiratory system (shape of the nose) to warm up cold air (source source)

Those traits have evolved naturally because cultural adaptations did not prevent natural selection entirely.

The supposed cold adaptations of improved heat retention through lower surface-to-volume ratio in cold indigenous people has, however, turned out to be a nutrition-related “issue” instead. In cold environments, humans consume more animal-derived, high-fat foods and less raw foods. Fruits and plant foods were often not readily available. Also, some nutrients can be short in supply in those environments, like iodine, selenium, or vitamin D.

Despite those adaptations to cold temperatures in cold-indigenous people, we all can acclimate through exposure to a small extent:

Optimizing thermoregulation and cold acclimation is as good as it gets

Even in temperate zones, during autumn and spring it would be a challenge to survive outside. Like all endotherm organisms, humans do have thermoregulation to immediately respond to changes in temperature. We can train the body to endure the cold for a short time to a limited extent, but that is about it! This is called acclimation and improves those responses to cold stress.

Thermoregulation and cold stress responses can also be improved by optimizing the intake of those nutrients, that play a role in thermoregulation.

However, improving cold tolerance through acclimation is limited! This so-called “phenotypic plasticity” is based on epigenetics, meaning we just squeeze out the best of our genetic makeup. Therefore acclimation do not reach the extent of genetic adaption to cold climates within evolutionary timelines.

Humans are a tropical species!

We often refer to tropical places as paradise and are willing to pay a small fortune to enjoy a holiday. Passing a few weeks in the tropics can help psychologically and improve health, too! In the tropics, our skin glows, and we feel calm but full of energy simultaneously. Generally, people living in tropical places are known to have a relaxed and friendly attitude and radiate health and energy.

We feel good in the tropics because we are adapted to warm climates

But why do we love the tropics so much? How is it possible that the in this climatic change, we experience health benefits? The answer is simple yet surprising: The human body is biologically best-adapted to tropical conditions!

We are a species that originated in tropical Africa. We have migrated faster out of our original habitat than evolution could act (see below how we managed to do so). One impressive, extreme example of rapid “re-adaptations” of humans migrating from cold climates into tropical climates is the Americas: “…humans adapted from being Arctic hunter-gatherers to Amazonian cultivators within a few millennia” (Scerri, E.M. et al. (2022) ‘Tropical forests in the deep human past’). This is an example that indicates that tropical climates are indeed “easy” for humans to adapt, because of our biological roots in the tropics, and relatively few evolutionary adaptations to cold environments while maintaining our “tropical genes”.

Our biology is that of a tropical great ape – when we live in cold areas, we are dislocated tropical beings!

While climatic changes do exist in tropical regions, too, they are minor compared to temperate climates. Temperature stress in the tropics is dominated by heat, to which humans, as good sweaters, have well-adapted. It’s safe to say that, biologically, all-year-round 25° temperatures are our comfort zone, where we survive without heating and even without cooking – which brings us to the next point: Our natural species-specific diet: a tropical frugivorous diet!

Humans are still a tropical species, biologically adapted to warm climates and a tropical frugivorous diet!

We are frugivorous animals – specialized in eating (tropical) fruits

Besides thermal adaptations, humans also have another interesting dietary adaptation to typical tropical foods: we are specialized fruit-eaters (frugivores) like our closely related chimpanzee family. Our dietary biology is another indication that humans are a species native to the tropics:

While frugivorous animals live in all climatic zones with fruit-baring plants, only tropical plants provide enough nutrition for specialized fruit-eaters all year round. For this reason, bigger frugivores (like apes) can sustain themselves only in a tropical habitat. This is why vitamin C and vitamin D are such a huge deal for health during winter when fruits and sunshine are not as abundant in our lifestyle.

The tropics are where we feel most comfortable all year round. It is the climatic zone where humans can survive without infrastructure for warming and even food production because the tropical forests are home to an abundance of highly nutritious fruits – all year.

How have we managed to migrate and live in colder areas?

Biologically, we still carry our tropical genes, so how have humans migrated to colder areas and survived the cold?

Usually, to a large degree, animal distribution depends on how well they physically tolerate temperature stress. Humans, however, have overcome their biological limitations: we have managed to live almost everywhere!

Culture and behavior instead of physical adaptations to cold climates

Only our intelligence and infrastructure can enable us to live in colder zones: humans survive(d) the cold mainly due to behavior, not genetics! We have used cultural adaptations and tools to survive in the cold (i.e., wearing fur, heating, and using tools) rather than letting biological evolution run its course.

By modifying the surroundings into a more suitable warm environment, humans were able to overcome the limitations set by biology. For example, wearing warm clothing and animal fur has enabled us to survive without genetically needing to grown our own fur. Wearing fur could, in an evolutionary sense, be looked at as the “natural appropriation” of the animals’ cold adaptation.

It’s likely that, without the skills and brain-power, humans simply would have stayed in our original tropical habitat – like our closest relatives, the apes. See more on this topic here.

It’s mind-blowing how people migrated into arctic regions! Cold-indigenous people withstand the cold with the use of thick furs and hats. Traditionally, inuits have a raw meat diet to obtain sufficient nutrition, including vitamin C. Those are just a few of many fascinating cultural adaptations as a response to their challenging environment. However, the life expectancy of inuits is relatively low.

We still imitate the tropics when living in colder climates

No wonder – considering our tropical biology – that up to today our cultural adaptations do one and the same thing: They imitate our ancestors’ tropical home, diet and climate. Or we actively pursue it.

  • Temperature: Heating and warm clothing are the two obvious ones. But also pools and spas are a great example: Spas make life a little easier for us in winter. Why do we love spas madly? Because they are a small piece of paradise, the tropics where we feel cozy for a few hours. We love to walk around in a warm moist environment decorated with tropical plants and warm waters to swim in. Most of us have difficulties entering cold water, and if we do, we do not stay long.
  • Sun: We supplement the sun through vitamin D and sun studios. Even our ancestors had to supplement vitamin D to prevent deficiencies. No wild animal requires any supplementation because they live within their natural habitat. Zoos are the best example of imitating the natural habitat of a species. For humans, we do it in much larger dimensions.
  • Foods: We import foods from warmer to colder climates to have healthy raw plant foods all year round. And we cook foods to get more nutrition from otherwise inedible foods.
  • Back to the Roots: We travel to warm places to relax and feel better.

Why no-one really stands winter, even if they say so…

There are always those people who claim to love winter and the cold… and we just don’t quite want to believe it, because we freeze! But be sure, it’s not you that is cranky, it’s them that misunderstand: No human really “likes” cold! Our body is not made to withstand freezing temperatures. The winter-lovers only enjoy winter because they are well-equipped for the cold and have the infrastructures that keep them cozy. We rely on warm houses, electricity, food imports, and top-quality winter gear to survive.

Sure, Some individuals have a slightly higher cold tolerance and do not suffer as quickly (learn how to optimize cold tolerance with foods and nutrients here). Still, generally, our biology is fragile in harsh winter climates… because biologically, we are still widely adapted to warm climates all year round.

All of this is not rocket science, but common sense… and still, this has to be brought to our awareness to understand what and who we are… at least biology-wise! Understanding our biology can be like a breath of fresh air in the confusing health and nutrition science jungle.


So next time someone says, they love winter, kindly ask them to undress and spend a night outdoors!

References

  1. Makinen, T.M. (2010) “Different types of cold adaptation in humans,” Frontiers in Bioscience, S2(3), pp. 1047–1067. Available at: https://doi.org/10.2741/s117.
  2. Daanen, H.A.M. and Van Marken Lichtenbelt, W.D. (2016) “Human whole body cold adaptation,” Temperature, 3(1), pp. 104–118. Available at: https://doi.org/10.1080/23328940.2015.1135688.
  3. Scerri, E.M. et al. (2022) ‘Tropical forests in the deep human past’, Philosophical Transactions of the Royal Society B: Biological Sciences, 377(1849). doi:10.1098/rstb.2020.0500. 
  4. Jablonski, N.G. (2018) “Evolution of human skin color and Vitamin D,” Vitamin D, pp. 29–44. Available at: https://doi.org/10.1016/b978-0-12-809965-0.00003-3.
  5. B. Handwerk, Why did Europeans evolve into becoming lactose tolerant? Smithsonian Magazine (2022) Available at: https://www.smithsonianmag.com/science-nature/famine-and-diseases-likely-drove-europeans-ability-to-digest-milk-180980483/ (Accessed: March 30, 2023).
  6. Stansfield, E. et al. (2021) “Respiratory adaptation to climate in modern humans and Upper Palaeolithic individuals from Sungir and Mladeč,” Scientific Reports, 11(1). Available at: https://doi.org/10.1038/s41598-021-86830-x.
  7. Author unknown, Thermoregulation: Types, how it works, and disorders. Medical News Today, Available at: https://www.medicalnewstoday.com/articles/thermoregulation#disorders (Accessed: March 30, 2023).
  8. Frugivore (2022) Wikipedia. Wikimedia Foundation. Available at: https://en.wikipedia.org/wiki/Frugivore (Accessed: March 30, 2023).
  9. Poikela, N. et al. (2020) “Multiple paths to cold tolerance: The role of environmental cues, morphological traits and the circadian clock gene vrille.” Available at: https://doi.org/10.1101/2020.04.20.050351.
  10. Newman, M.T. (1956) “Adaptation of man to cold climates,” Evolution, 10(1), p. 101. Available at: https://doi.org/10.2307/2406102.
  11. P. Gadsby, The Inuit paradox. Discover Magazine (2020) (available at https://www.discovermagazine.com/health/the-inuit-paradox).
  12. Life expectancy in the Inuit-inhabited areas of Canada, 1989 to 2003 – Findings. Health Reports: Life expectancy in the Inuit-inhabited areas of Canada, 1989 to 2003 (available at https://www150.statcan.gc.ca/n1/pub/82-003-x/2008001/article/10463/4149059-eng.htm).
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Martina Spaeni Lima, MSc

"We are frugivores - specialized fruit-eaters!" It was passion at first sight when I came across the intriguing concept that humans are adapted to a high-fruit diet, similar to chimpanzees...

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