Human Biological Adaptability

1. Human Biological Adaptability Most of this PowerPoint came from HERE

2. Overview • ability to rapidly adapt to varying environmental conditions • made it possible for us to survive in most regions of the world • most other species are restricted to one or relatively few environments • humans normally respond to environmental stresses in four ways (first 3- biological, last one- cultural):

3. genetic change • individuals inherit advantageous trait(s) • more likely to survive longer and pass on genes to the next generation • ability to produce sweat for cooling our bodies in hot environments • sickle-cell trait among the people of Central Africa • A Mutation Story (4:50)

4. developmental adjustment • occurs in childhood and typically results in anatomical and/or physiological changes that are mostly irreversible in adulthood • have a high degree of physiological plasticity • can be physically molded by our environment during the growing process • result from both natural environmental pressures and cultural practices

5. the now illegal custom in China of tightly wrapping or binding the feet of young girls • in China today the surgical breaking of the two lower leg bones in both legs and then using adjustable metal braces to progressively extend the length • in the late 19th century tight corsets worn by girls when their bodies were still growing (a 19 inch circumference was the ideal) • customary for middle and upper class parents to have the teeth of their children straightened with retainers and braces

6. acclimatization • forms of adjustment to environmental stresses that are usually reversible • acquire dark skin tans during the summer months and lose them during the winter • difference in pressure experienced in mountains, flying, diving, can usually be cancelled out by yawning, swallowing, or chewing gum

7. Cultural Practices and Technology • over the last half million years at least, we invented technological aids that allowed us to occupy new environments without having to first evolve biological adaptations to them • houses, clothing, and fire

8. Specific Human Adaptations • Climate Extremes • have unusually efficient internal temperature regulating systems that automatically maintain stable core body temperatures • Bergmann's Rule • the more cells an animal has, the more heat it will produce • larger animals usually have a smaller surface area relative to their body mass

9. Negative correlation between environmental temperatureand body mass in warm blooded animals

10. Allen's Rule • the length of appendages also has an effect on the amount of heat lost to the surrounding environment • members of the Masai tribe of East Africa are normally tall and have slender bodies with long limbs that assist in the loss of body heat • in cold environments, a stocky body with short appendages would be more efficient at maintaining body heat

11. High Altitude • the lower air pressure makes it more difficult for oxygen to enter our vascular systems

12. successful populations are those whose ancestors have lived at high altitudes for thousands of years • results in some populations being genetically more suited to the stresses at high altitude, may… • produce more hemoglobin • increase their lung expansion capability • breathe faster in order to take in more oxygen • have broader arteries and capillaries

13. Skin Color Adaptation • skin color is due primarily to the presence of a pigment called melanin • acts as a protective biological shield against ultraviolet radiation • ~90% of vitamin D is synthesized in their skin and the kidneys with the help of UV radiation • skin's ability to tan in summertime is an acclimatization to this seasonal change • some Northwest Europeans have substantially lost the ability to tan as a result of relaxed natural selection • nature has selected for people with darker skin in tropical latitudes

14. Nina Jablonski breaks the illusion of skin color (14:46) http://www.ted.com/talks/lang/eng/nina_jablonski_breaks_the_illusion_of_skin_color.html

15. Nutritional Adaptation • some people live well on daily diets that would be at a starvation level for others • adapting to local nutritional opportunities has led to the evolution of related genetic differences among the populations of the world • the best documented differences in nutritional adaptation relates to milk sugar, or lactose • the gene that codes lactase is on chromosome 2. • lactose intolerance is at its highest frequency in some parts of Africa, East Asia, and among Native Americans • northern Europeans generally have the lowest frequency of this “dietary problem”

16. Evolutionary Significance of Lactose Tolerance • ability of people in Europe and some other areas of the world to continue producing lactase as adults is very likely a relatively recent evolutionary development • prior to the domestication of cattle, sheep, goats, and horses after about 9000 years ago, milk was most likely only consumed by babies and very young children • dairy products such as cow's milk, yogurt, and cheese did not exist • When nutrient rich nonhuman milk became widely available in socities, the rare genetic variations that allowed some adults to easily digest lactose were selected for and this trait became more common • natural selection shifted to favor lactose tolerant people

18. Adapting to Alcohol • likely that natural selection is largely responsible for population differences in the ability of humans to quickly metabolize alcohol in beverages • metabolizing alcohol eliminates its toxicity and removes it from the blood so that it won't cause cell and organ destruction • frequencies of the genes coding for the enzymes involved in this protective process vary significantly from population to population • beer and wine consumption have been common in Europe and the Near East for 5-6 thousand years • many people in these same populations now have the genetic makeup that gives them a relatively high tolerance of alcohol • in contrast, alcohol tolerance is unusual among Native Americans • with few exceptions, they have only had alcohol based beverages since the arrival of Europeans, a few hundred years ago • it is not surprising that alcoholism and alcohol related problems such as cirrhosis of the liver are at comparatively high rates among many Native American groups.