ANT2000 10 6 16 Ecogeographic Rules o Bergmann s Rule 1847 within a broadly distributed taxonomic grouping populations with individuals of larger size are found in colder environments and populations with individuals of smaller size are found in warmer regions o Allen s Rule 1877 the body shapes and limb proportions of warm blooded creatures vary by climatic temperature by either minimizing exposed surface area to maximize heat loss in hot climates Skin Color o Varies due to Transparency of skin Amount of carotene Amount of melanin o Melanin is a dark pigment produced by melanocytes in the epidermis of the skin o People with darker skin have more melanocytes than people with lighter skin o Exposure to sunlight increases melanin production causing skin to tan and protecting it from overexposure to UV radiation Vitamin D o Vitamin D deficiency can lead to all sorts of circulatory respiratory and muscle problems Because vitamin D maintains calcium balance for healthy bone development deficiency can lead to maladies like rickets o Culture matters too because vitamin D can be supplied through diet as well as synthesized with help of sunlight Polymorphisms o For traits controlled by a single gene like blood type variations in phenotypes are determined by relative frequencies of alleles across populations These genetic variants are known as polymorphisms o There are three types of alleles for blood type A B O and four possible phenotypes A B O AB o Polytypic features occur when polymorphisms are distributed among geographically dispersed populations Sickle Cell Balanced Polymorphism o Sickle Cell is an example of a polymorphism due to a mutation that is deleterious in the homozygous genotype If the sickle cell allele is inherited from both parents the individual will suffer anemia circulatory problems and often early death o Why would its frequency increase and be maintained if it is so dangerous Indeed in Western and Central African populations the sickle cell allele reaches levels close to 20 Malaria o Caused by a protozoan parasite carried in mosquitos malaria is common in the same places where the sickle cell is prevalent It is no coincidence individuals bearing one sickle cell allele show greater resistance to malaria because their red blood cells offer a less conducive environment for the parasite to reproduce Among normals malaria thrives the homozygotes have virtually total resistance to malaria but do not otherwise survive often Selection favors the heterozygotes called balanced polymorphs thus maintaining the sickle cell allele at substantial frequency Racial bias that accumulates and is compounded by an array of societal policies practices and other norms that work to reinforce racism Too 2 often taken for granted as natural and often overlooked because they are hidden 3