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Lecture 12

Lecture 12 - Human Adaptation Part 1

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Esteban Parra

Human Adaptation I Humans and the Changing Environment - Humans occupy a wide geographic range, living under all kinds of environmental conditions. - It is important to mention that the environment not only comprise external factors, such as temperature or humidity, but internal factors as well, such as infectious diseases. o I.e., Malaria  many regions of the genones have been selected based on the genome of malaria - In this lecture we will review ways in which humans respond to environmental challenges. Some Ways to Respond to the Environment - There are four main ways in which humans respond to environmental stresses o Cultural practices and technology o Acclimatization o Developmental adjustment o Genetic adaptation - We will review very briefly each category and study in more detail different examples of genetic adaptation. - Note: biological responses - Note: involves inherited genetic changes Cultural Practices and Technology - There are uncountable examples on how culture and technology have allowed humans to adapt to multiple environments. - Since the origin of anatomically modern humans, this has become our main adaptive strategy. - Of course, humans have been perhaps too successful with this approach. - We are increasingly a driving factor causing environmental changes that can affect us and every other life form in the planet. Acclimatization - Acclimatization can be defined as the physiological adjustment of individual organisms to different conditions (e.g., temperature, altitude, photoperiod). - Acclimatization is a reversible process, which entails no genetic change. - The length of time in which these reversible changes occur can be quite variable. Some times they occur very quickly (short-term acclimatization, or acclimation), some times they can take much longer, even years (long-term acclimatization). Examples of Acclimatization - Increase in sweating in hot temperatures. - Increase in respiration rate, heart rate, and red blood cell production when moving to high-altitude environments. - Tanning response under increased UV radiation o Immediate tanning (within 1-2 hours of exposure) fades away during the first 24 hours.  It is a redistribution of melanin that you already have o Delayed tanning (within 2-3 days of exposure), can last several months. Developmental Adjustment - Developmental adjustment can be defined as anatomical or physiological changes occurring during growth or development as a result of environmental stresses. o These changes can be difficult to reverse or even irreversible. - The ability of organisms to respond physiologically or developmentally to environmental stresses is often termed plasticity. Some Examples of Developmental Adjustment - Reduced body size of adults who had inadequate childhood nutrition, or - Increased height as adults of persons with good nutrition during childhood. - Greater chest dimensions and lung capacity in persons that migrated at early age to high- altitude environments. Adaptation - Adaptations can be defined as inheritable genetic changes that develop in populations over long periods of time. o Related to natural selection (altering the frequencies of alleles  it is a slow process) - Adaptations are inheritable, acclimatizations are not. - Adaptations are the result of the action of natural selection, increasing the overall fitness of a population. This is how evolution works. o Entails genetic information that is passed from generation to generation - Through the remaining portion of the lecture, we will review interesting examples of adaptation. Some Examples of Adaption - Perhaps the best known example of adaptation is sickle cell trait. - In this case, the environmental factor involved is malaria, a tropical disease caused by a parasite, mainly Plasmodium falciparum (although there are other three Plasmidium species causing milder forms of malaria). o This is the nastiest of the 4 plasmodium parasite Understanding Malaria (Not part of the slide but important) - Malaria is a tropical disease, common in regions of Central and South America, Africa and Asia - Malaria is caused by protozoa of the genus Plasmodium (P. falciparum, P. vivax, P. ovale, P. malariae). Plasmodium invades red blood cells, causing the disease - The disease is spread by the mosquito Anopheles - Symptoms include cills, fever, shaking, profuse sweating and fatigue - The most severe form of the disease, cause by P. falciparum, is often fatal - According to the WHO 2010 Malaria report, there were approx.. 219 million cases of malaria and approx.. 660,000 deaths in 2010 A Brief History of Malaria in Africa - Malaria became a very serious problem in Africa only relatively recently. - The arrival of horticulture to tropical Africa a few thousand years ago, substantially changed the ecological conditions, which became ideal for the growth and spread of the mosquito Anopheles. - Thus, malaria is a good example of how ecological changes due to human cultural adaptations can influence disease patterns. Malaria and the Sickle Cell Mutation - A mutation in the Beta-chain of the hemoglobin molecule (responsible for oxygen transport) appeared in Africa, and has increased in frequency in areas where malaria is prevalent. - This mutation changes the amino acid Glutamic acid normally present in position 6 of the Beta-chain to the amino acid Valine. - Sequence of the normal (Hb A) and sickle cell (Hb S) alleles in the Beta chain of hemoglobin. o Responsible for sickle cell anemia, this one change of letter from the ancestral sequence - The Beta chain gene is located on chromosome 11. Hb S and Sickle Cell Anemia - Individuals homozygous for the Hb S allele develop a form of anemia named sickle cell anemia. - The half-life size of red cells of sickle cell patients is much lower than the normal red cell half life. o Because of this change, the red blood cells will be destroyed at a much faster rate (relative to normal red blood cell) - Red blood cells of sickle cell patients change their shape when they release oxygen to the peripheral tissues of the body. o When the red blood cells delivers the oxygen, it also changes the elasticity of the cell that start to attach to each other and start to block pathways that create problems - They form hemoglobin polymers that can block cell flow and interrupt oxygen delivery. o This is a recessive disease  heterozygotes are carries but not affects, but can pass on Inheritance of the HB S alleles - We have seen that homozygotes for the Hb S allele develop sickle cell anemia. - Hb AS heterozygotes are phenotypically normal. They are said to have the sickle cell trait. Although phenotypically normal, they can transmit the Hb S allele to their progeny. - Take a look at some possibilities of inheritance, d
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