Anthropology: The Exploration of Human Diversity 5 Human Variation and Adaptation Anthropology: The Exploration of Human Diversity 11th Edition Conrad Phillip Kottak

Human Variation and Adaptation Race: A Discredited Concept in Biology Human Biological Adaptation

Race: A Discredited Concept in Biology Race refers to geographically isolated subdivision of a species Members of race or subspecies share distinctive physical characteristics based on common ancestry and inheritance of same genes Human populations have not been isolated enough from one another to develop into discrete races

Race: A Discredited Concept in Biology Human populations vary biologically, but because of extensive gene flow and interbreeding, there are no sharp breaks between populations Human biological variation distributed gradually between populations along clines

Race: A Discredited Concept in Biology Scientists have trouble grouping people into distinct racial units Race is supposed to reflect shared genetic material Early scholars used phenotypical traits (skin color) for racial classification

Race: A Discredited Concept in Biology Races Are Not Biologically Distinct Obvious problem with “color-based” racial labels is that terms don’t accurately describe skin color Another problem with tripartite scheme is that many populations don’t neatly fit into one of the three “great races”

Race: A Discredited Concept in Biology Racial classifications based on phenotype lack credibility because similarities and differences don’t necessarily have genetic basis

Race: A Discredited Concept in Biology Explaining Skin Color Natural selection—process by which nature selects the forms most fit to survive and reproduce in a given environment

Race: A Discredited Concept in Biology Explaining Skin Color Skin color influenced by several genes Melanin—primary determinant of human skin color; chemical substance manufactured in the epidermis Prior to 16th century, darker skinned populations closest to the equator

Race: A Discredited Concept in Biology Explaining Skin Color Skin color influenced by several genes Unprotected humans in tropics face threat of severe sunburn Increases susceptibility to disease Impairs the body’s ability to withstand heat by reducing the skin’s ability to sweat Light skin is more susceptible to skin cancer. Loomis suggested that in tropics, dark skin color protects body against overproduction of vitamin D

Human Biological Adaptation Abundant evidence for human genetic adaptation and evolution through selection working in specific environments

Human Biological Adaptation Genes and Disease According to World Health Report, tropical diseases affect more than 10 percent of world’s population Malaria—300 million to 500 million people Schistosomiasis—more than 200 million Filarisasis—120 million

Human Biological Adaptation Genes and Disease Microbes major selective agent for humans, particularly before arrival of modern medicine After food production emerged, infectious diseases pose mounting risk and became foremost cause of human mortality ABO blood groups vary in resistance to disease

Human Biological Adaptation Genes and Disease In diseases for which there are no effective drugs, genetic resistance maintains significance There is probably genetic variation in susceptibility to HIV AIDS could cause large shifts in human gene frequencies

Human Biological Adaptation Facial Features Natural selection also affects facial features Long noses seem to be adaptive in arid areas and cold environments Thomson’s Nose Rule—association between nose form and temperature

Human Biological Adaptation Size and Body Build Bergmann’s rule—smaller of two bodies similar in shape has more surface area per unit of weight Average body size tends to increase and cold areas and decrease in hot ones Allen’s rule—relative size of protruding body parts—ears, tails, bills, fingers, toes, and limbs—increase with temperature

Human Biological Adaptation Size and Body Build Human populations use different, but equally effective, biological means of adapting to environmental stresses associated with high altitudes

Human Biological Adaptation Lactose Tolerance Phenotypical adaptation—adaptive changes that occur during individual’s lifetime Genes and phenotypical adaptation work together to produce a biochemical difference between human groups in ability to digest large amounts of milk Adaptive advantage when other foods are scarce and milk available