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I. Race: A Discredited Concept in Biology A. Races Are Not Biologically Distinct B. Explaining Skin Color II. Human Biological Adaptation A. Much of the human biological diversity is the result of human genetic adaptation to specific environments. 1. The high frequencies of the HbS heterozygote in malarial environments are a good example. 2. Some alleles that were once maladaptive can lose their disadvantage if the environment changes. 3. The Human Genome Project is working to map all of the genes and chromosomes found in humans. a. Many of today’s incurable hereditary diseases someday may be rendered evolutionarily neutral through genetic therapies. b. One downside of this research is that it can also lead to genetic discrimination (eugenics). B. Genes and Disease 1. Despite the advances in medical research over the last 100 years, diseases still pose a significant threat to the health of human populations all over the world. 2. Human blood factors play an important role in resistance to some diseases. a. There is evidence that the various alleles producing human blood types interact with infectious and noninfectious ailments. b. For example, the presence of type A blood cells seems to make a person more susceptible to smallpox. C. Facial Features 1. Thomson's nose rule asserts that noses tend to be longer in colder climates. 2. The Australian Aborigines' sand-permeated diet has selected for larger teeth than seen in other populations. D. Size and Body Build 1. Different climates have selected for different body shapes. 2. Bergmann's rule: because of the respective ratios between mass and surface area, smaller bodies dissipate heat faster, and larger bodies retain heat better; thus more larger animals are found in colder habitats, while smaller animals have been selected for in hotter habitats. 3. Allen's Rule: slender bodies with long limbs dissipate heat more efficiently and are selected for in tropical climates; heavy, short-limbed bodies retain heat better and are selected for in colder climates. E. Lactose Intolerance 1. The term phenotypic adaptation refers to changes which occur to an individual organism during it's lifetime which enhance its reproductive fitness. 2. Individuals from herding populations in northern Europe and parts of Africa maintain their ability to digest milk (continue to produce the enzyme, lactase) into adulthood, whereas people from other populations can digest milk (specifically, milk sugar, called lactose) only during childhood. 3. The fact that descendents of these herding population who no longer herd continue to be lactose tolerant as adults indicates genetic adaptation to a milk-rich diet. 4. The fact that lactose intolerance can vary during an individual's adult life, depending on how much milk is consumed, indicates that some phenotypic adaptation also takes place. |