In chapter 7, Coyne discusses how speciation depends mostly on geographic isolation. Differences in geography cause a species to develop different adaptations to suit their environment. Although humans today have evolved fairly convergently, our species have also developed adaptations based on our geographic locations. While today’s technology almost completely eliminates isolationism between humans, in the past, humans were restricted by the same geographic barriers as animals (i.e. mountains, oceans, etc). An example of an adaptation is skin color, where humans living in regions where the intensity of the sun is higher have darker skin to protect against excess UV light. Besides the example given above, what other adaptive differences have evolved from geographic isolation between humans and how has that adaptation helped humans survive?
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One popularly studied result of geographic isolation between humans is the adaptation to high altitudes.
ReplyDeleteWhen a resident of a sea level location visits a high altitude location (>8,000 ft above sea level) the body suffers various illnesses. These illnesses are caused by a smaller oxygen intake per breath and lower pressures. To acclimate to the new environment, mountain climbers and hikers must move slowly, spending 1-3 days getting used to the lower oxygen levels (http://www.princeton.edu/~oa/files/altitude.pdf).
Andean and Tibetan lands rise 13,000 feet above sea level. Populations in the Andes have adapted to the thin air by maintaining higher hemoglobin concentrations in their blood. In this way, breathing rate does not have to change, but the additional hemoglobin carry more oxygen through the blood stream. Furthermore, natives have developed an increase in enzymes that facilitate the dissociation of oxygen from hemoglobin to body tissues (creating a more efficient process of oxygen transport). The structure of hemoglobin (a protein with tertiary and quaternary structre) alludes to its function; Each hemoglobin has 4 iron molecules, and each iron molecule can attach one oxygen molecule. Thus, increasing the amount of hemoglobin in blood flow increases the oxygen content of blood by four for each molecule.
On the other hand, Tibetans have had respiratory adaptations to solve the problem of thin air. These people develop larger total lung capacities than people from low altitudes (total lung capacity = residual volume + vital capacity). Tibetans also have an increased breathing rate. They possess lungs that synthesize more nitric oxide, initiating vasodilation and a higher blood flow to counter the lower oxygen content. Dilation of the capillaries also enhances oxygen transport to body tissues through diffusion.
By evolving these adaptations high altitude populations avoid the nausea, vomiting, breathlessness, cerebral edema, pulmonary edema, and potential death that may result from high altitude sickness or hypoxia and survive and reproduce after acclimating to their local conditions.
http://www.americanheart.org/presenter.jhtml?identifier=4618
http://news.nationalgeographic.com/news/2004/02/0224_040225_evolution_2.html
In addition to the changes in blood and lung composition in high altitudes, as mentioned above by Eilrayna, there are also physiological changes in the basic structure of humans that live in high altitudes. Studies show that people who live at higher altitudes, such as in the Andes or Tibet, are shorter, have larger chests (“barrel chests”) to hold larger lungs, and shorter legs and frames. Eilrayna explained the significance of having larger lungs in order to maintain homeostasis by to properly maintaining blood oxygen levels. The “barrel chest” developed in order to hold the larger lungs, which then in turn could filter the necessary gases more efficiently than, say, a Chicagoan’s smaller, less acclimated lungs. Increased hemoglobin concentration and lung development can result by training in higher altitudes, which is why Olympic athletes often train at the higher altitudes.
ReplyDeleteAccording to the article found on JSTOR, “Adaptation to High Altitude,” “babies born at high altitude are shorter as well as lighter.” The shorter stature of the people who live in mountains can be equated with several factors. The Andes and Tibet are both often cold places, as well as being many thousand feet above sea level and steep in places. Stockier legs, with thicker, stronger muscles, help those who live in steep mountains climb further without tiring. Their muscles have also been found to be more efficient than those of humans living at lower altitudes, in similar to the efficiency of their lungs.
Their smaller frames would also mean less work (force over distance) would have to be done in order to transport the hard-earned oxygen from the lungs to the rest of the body. The reduced surface area of their bodies would also reduce heat loss. Certain peoples have also developed specialized soles of their feet, with thick skin and “many more blood vessels than the lowland people,” helping their feet stay warmer and not freeze. These adaptations, in addition to hemoglobin and lung capacity, help the Andean and Tibetan people survive in their high altitude environment.
(http://www.jstor.org/pss/2155649 <-what’s this a journal article aaaaahhhh)
(http://www.morning-earth.org/graphic-E/Transf-Adapt.htm)
Another adaptation due to the geographical isolation of human beings is based on the temperature of the environment; developing the optimum body type for the most effective thermoregulation for the environment.
ReplyDeletePeople from areas that are extremely hot have generally adapted to the intense heat by developing longer, leaner limbs. The longer limbs allow for a greater surface area for more evaporative cooling to occur. Evaporative cooling is when the water in the body evaporates off of the skin. The water retains heat, so when the water evaporates, the heat is taken out of the body as well, thereby effectively cooling the body (Campbell 865). Also, when the body limbs are leaner, the fat in the body is not as compact, which makes it more difficult to retain heat in the body. Not only are the limbs longer and leaner, the entire body in general may be larger (height?)in order to further increase the amount of surface area available for evaporative cooling.
Conversely, in arctic and freezing environments, humans have adapted to the lack of heat by becoming stockier, with shorter limbs and a larger mass. Having shorter limbs minimizes the skin surface area, therefore minimizing the amount of heat loss by evaporative cooling, and having a body with more layers of compacted fat helps retain heat by insulation.
Some more examples of adaptations of people living in colder climates include increased metabolism rates, more insulation of body organs, as well as changes in blood flow. The Inuit from Alaska, for example, eat foods high in calories and fats, which increases the metabolic rate. When the metabolic rate increases, the amount of body heat increases as well. This could be due to nonshivering thermogenesis, where the mitochondria increase the metabolic activity and istead of generating ATP, generate heat (Campbell 866).
The Aborigines of Australia have developed so that fat accumulates around the chest and stomach areas in order to further insulate the vital organs in the torso. Also, at night, the blood vessels of the Aborigines vasonstrict. Vasoconstriction reduces heat transfer to the skin surface, which therefore minimizes the amount of heat loss from the skin surface (Campbell 864).
These thermoregulatory adaptations have helped the people in extreme weather conditions to survive in many ways. In hot climates, the minimization of heat retention decreases the chances of overheating. If the temperature in the body gets too high, then it runs the risk of denaturing proteins, which then will be unable to function and therefore the body will be unable to function and the person could die. In cold climates, maximizing the amount of heat retention keeps the people from freezing to death.
This prompt relates to the biological theme of relationship of structure and function. The structure and formation of the human body in the different climates contribute to the function of survival of the person in that climate. This prompt also relates to the theme of evolution, in that the georaphic isolation has led to certain small evolutionary adaptations in the people of different climates.
http://anthro.palomar.edu/adapt/adapt_2.htm