Adaptive significance Infectious disease environmental factors have challenged the human species throughout its evolutionary timeline we will discuss these challenges and consider how humans have met them organisms must maintain normal functions to survive Homeostasis balance within a biological system Stress in a physiological context acts to disrupt stasis Adaptation refers to long term evolutionary changes genetic acts on the population or species level examples sweating pigmentation of skin Acclimatization physiological responses to environmental conditions cid 127 maintained by the interaction of physiological mechanisms that compensate for changes internal and external acts on individual level but can be used as an example for a population or species 3 forms Short term acclimatization change in physiology temporary and rapid adjustment to an enviromental change body adjusts compensates for stress example increase in hemoglobin production at high altitudes to permit the body more O2 oxygen Long Term acclimatization same as short term but lasts several months after exposure to new environment has ceased the physiological adjustments remain example hemorrhaging of blood vessels in Scurvy sufferers Developmental acclimatization results from exposure to an environmental stressor during growth and development incorporated into individual s physiology not reversible permanent example rickets from Vitamin D deficiency Responses to Solar Radiation darker skin in tropics lighter skin in northen latitudes pigmentation influenced primarily by melanin cid 127 melanin absorbs UV rays protects from overexposure and helps prevent cancer sun exposure temporary increase in melanin production acclimatization exception albinos NS favors dark skin in areas near equator early hominids lived in tropics outdoors no clothing selective pressures changed when migrated out of Africa cid 127 more clouds less sun fewer daylight hours fire clothing to keep warm dark skin not as important melanin production relaxed Vitamin D Deficiency Vitamin D is necessary for bone mineraliztion and growth primary source is from the reaction between UV rays and cholesterol found in the skin Adequate exposure to sunlught is essential for normal bone growth insuffiecient amounts will result in rickets in childhood or osteomalacia in adults Vitamin D Hypothesis Need for Vitamin D production in skin probably most significant selective force for depigmentation example Northern African Americans vs Southern African Americans Responses to Thermal Environments Evaporative Cooling sweating perspiration from sweat glands evaporates on surface losing heat have equal sweat glands 1 6 million individual Is expensice to the body due to water sodium loss Vasodilation blood vessels expand increase blood flow to skin heat radiates from core to skins surface Body Size and Proportions to Regulate Body Temperature body proportions vary clinally in humans and animals in relation to environmental temperature varies little by little as you move through geographic space Bergmann s Rule correlates enviromental temperature with body mass in warm blooded animals body mass will increase with latitude and colder climates example of a cline seen in mammals cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 As mass increases a lower surface area to volume ratio is achieved so larger animals radiate less body heat per unit of mass stay warm of cold ex Polar Bears for humans the rule is true to certain extent Allen s Rule associated with size of body extremities endothermic animals with the same volume may have differing surface areas this will aid or impede their temperature regulation colder climates usually have shorter limbs than the equivalent animals from warmer climates Hypoxia reduced concentration of oxygen at higher altitudes which elicits a physiological response example in book cold environments squat round bodies with short extremities warm environments long cylindrical bodies with long extremities Responses to Cold Environments cid 127 more energy required to produce heat than to retain it energy derived from diet short term response cid 127 metabolic rate and shivering vasoconstriction decreased blood flow to extremities and skin long term response variation intermittent periods of vasoconstriction and vasodilatation cultural factors such as fire High Altitudes stressors cold radiation dry environment poor nutrition acclimatiztion in visitors upon exposure increased respiration heart rate increase blood flow immediate increased RBC plasma more fluid and oxygen blood thickens days increased capillary network around cells better circulation years effects higher infant mortality impaired maternal fetal transport of oxygen cid 127 miscarriage and premature births delayed growth and maturation rates Barrel chest the thorax being rounder than normal the antero posterior diamete increased evelopmental acclimatization leads to greater lung capacity and a larger heart Infectious Disease caused by intro of a pathogen foreign microorganism viruses bacteria fungi example sickle cell anemia and Malaria vector agent that transmits disease cid 127 mosquitoes malaria fluids HIV rusty nail tetnis are communicable passed from person to person directly zoonotic transmitted to humans through contact with nonhuman animals cid 127 magnitude epidemic wave of disease SARS 2003 or Ebole in Congo 1995 endemic continuously present in a population pandemic over vast amount of geographic space flu HIV and SARS HIV and Smallpox some individuals test positive for HIV but show few if any symptoms even after 10 years suggest some may possess a natural immunity cid 127 mutant allele results in malfunctioning receptor site HIV unable to bind homozygotes may be completely resistant heterozygotes disease progresses slower cid 127 mutant allele found in 10 of European descent populations allele isnt a response to HIV but selection against an earlier pathogen requiring the same receptor site 1999 researchers show that a smallpox like virus uses same receptor site as HIV cid 127 may be reason mutant allele exits 18th century smallpox resposible for 10 15 of all deaths in Europe infectious diseases exert