Cold Life

Select only ONE of the following environmental stresses: (a) heat, (b) high levels of solar radiation, (c) cold, or (d) high altitude. Discuss specifically how this environmental stress negatively impacts the survival of humans by disturbing homeostasis. 

Cold climates create stress on the body that disturbs homeostasis by lowering our normal core body temperate range of 97.6 ˚- 99.6˚ to subnormal levels. When our core body temperate declines to 94 ˚, we begin to develop a condition known as hypothermia. Hypothermia occurs when our hypothalamus is unable to keep our core body temperate stable and we reach subnormal levels of temperature; cold climate is only one cause of hypothermia. Once our temperature decreases to extreme levels of 85 ˚F, our thermoregulation system fails and body temperature begins to drop rapidly resulting in organ failure and death. 

Symptoms range in mild to severe hypothermia. In mild hypothermia (89˚ -95 ˚), symptoms such as shivering, our blood vessel narrowing — vasoconstriction—, increase in heart rate, breathing and blood pressure and an onset of confusion and fatigue occur. In moderate hypothermia(82 ˚ -89 ˚), the shivering stops while confusion increases, metabolic rate drops, loss of fine motor skills, body alternates between vasoconstriction and vasodilation to avoid frostbite and gangrene (cycle is known as Lewis hunting phenomenon) and heart rate, breathing and blood pressure decreases. In severe hypothermia (<82 ˚), people experience extreme confusion and memory loss causing abnormal behavior such as taking clothing off, organs  — primarily the heart and liver — begin to shut down to conserve heat and protect the brain — causing irregular and/or weak pulse, slow brain activity and breathing — and a decline in consciousness which leads to a coma-like state and eventually death, as organs begin to fail.

Identify 4 ways in which humans have adapted to this stress, choosing one specific adaptation from each of the different types of adaptations listed above (short term, facultative, developmental and cultural). Include images of the adaptations.

Short term: Short term adaptations such as goosebumps, shivering, and cutaneous vasocontraction occur in response to cold weather. Shivering is the rapid movements of muscles as our body tries to produce more body heat; goosebumps occur when our arrector pili, a vestigial trait, contract in response to the stress such as cold weather and make the hair on our body stand up, forming bumps on our skin — arrector pili provided our mammalian ancestors with insulation as the hair on their bodies became erect and trapped air in them, and as a scare tactic to avoid being eaten (i.e. a porcupine); Cutaneous vasocontraction is the narrowing of blood vessels on the surface of skin that allows bodies to retain more heat as the skin acts as an insulator between outside stimuli and vital organs — the brain and heart — delivering more oxygen to them.

Facultative: The Inuit have a diet high in fats and calories, greatly increases their basal metabolic rate, which, in turn, allows one to produce more body heat as they burn the food they digest. Furthermore, this allows them to handle the gluconeogenesis process better (turning protein and fats into usable glucose); making their livers larger and increasing their volume of urine to digest what they eat better. On the other hand, the Ju/'hoansi of Southwestern Africa and the Aborigines of Australia — which live in environments that rarely face temperatures that stay below freezing for long and do not have diets high in fats — respond distinctly different physiologically to the cold: they develop thick fat insulation around their vital organs of the chest and abdomen; and long-term changes in their blood flow — vasoconstriction  — to retain heat. However, if they lived in an environment that stayed below freezing for long periods, they would suffer from frostbite and gangrene.

Developmental: People who live in colder climates are usually genetically shorter with high body mass and short appendages, which help produce and retain more heat than anyone who is taller with low body mass and long appendages. This was observed by Carl Bergmann, a German biologist in 1847, and Joel Allen, an American biologist in 1877. Carl Bergmann observed a negative correlation between body mass and environmental climate, and body shape/height (surface area) in relation to the rate of heat loss – coined Bergmann’s rule. On the other hand, Joel Allen noted a correlation between the length of appendages (more surface area) and rate of heat loss — coined Allen’s rule.

Cultural: Clothing, houses, diets high in fat, fire, and technology (heaters) are all cultural adaptations that allow us to keep warm in cold climates. The Inuit would build specialized homes out of tightly packed snow bricks that prevented the cold wind from entering, keeping warm air in and allowing them to build fires inside. Moreover, they made clothes and boots out of animal hide; to keep warm they would put the animal hide on the floor and huddle up together. Their diets — which were high in protein and fat — also allowed them to retain more body heat due to their increase in body mass. The Indians of Tierra del Fuego had similar cultures to that of the Inuit — which lived in the southern hemisphere while the Inuit were in the northern end.  




3. What are the benefits of studying human variation from this perspective across environmental clines? Can information from explorations like this be useful to help us in any way? Offer one example of how this information can be used in a productive way.

Studying human variation across environmental clines allow us to acquire knowledge in how our bodies react and adapt physiologically to climate and altitudes over short periods to long periods of time. It also allows us to study the phenotypic expressions and cultural adaptations in relation to the environment (i.e. skin color, height, diet and homes). Furthermore, with this information we have been able to create technology that has helped us withstand and acclimatize to different sets of conditions. For example, when someone is about to climb a mountain such as Mount Everest, they need to bring the proper equipment and clothing for it. Before climbing, they must acclimatize at separate camps on the mountain by ascending to high altitudes during the day and returning to a lower altitude to rest. To make the acclimatization process easier, they also increase their carbohydrates intake and lessen their protein and fats intake, drink around 1 gallon of water per day to help flush the kidneys of bicarbonate from an increase in respiratory rate, and use bottled oxygen tanks to compensate for the minimal oxygen. 4. How would you use race to understand the variation of the adaptations you listed in #2? Explain why the study of environmental influences on adaptations is a better way to understand human variation than by the use of race.  

Race is socially constructed and, therefore, can not be used to understand genetic adaptations; if it did, every separate race would look almost identical to each other. By studying environmental influences, we are able to see how they influence our appearance. For instance, although the Inuit live in latitude with fewer UV rays than at the equator, most retain a medium to dark skin pigment. Some of our dark-skinned ancestors — as they migrated into Europe and Asia, exposing themselves to different levels of UV rays — weren’t able to absorb enough sunlight to produce vitamin D, which played against them. Through natural selection, they started to adapt and populations with less melanin were created. However, the Inuit’s diet has consisted primarily of fish — which are high in vitamin D; this has allowed them to not depend on the sun for vitamin D production, retaining a high level of melanin. Although, their skin color can also be explained by how long they have lived in their environment — which has not been long enough for them to adapt less melanin — and by simply acknowledging that their were dark-skinned. Everyone, from different races and latitudes, develops different adaptations according to their genes and environment, not by racial terms. Thereby, we can not use this subjective social system to study biological variation.