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Department
Biology
Course
BIOL 1500
Professor
Marie Therese Rush
Semester
Winter

Description
Unit 8: Evolution and Disease Why Do We Get Sick? -human body is fallible to disease -human heart has number of valves that open and close approximately 2.5 billion times over a lifetime -heart valves are prone to failure for variety of reasons -artificial heart valves have been developed to prolong life(haven’t created perfect artificial heart valves yet) Darwinian Medicine -Neese (physician) and William’s (evolutionary biolog) book questions why we get sick and propose six evolutionary causes of illness or disease: defense, infection, novel environment, genes, design compromise, and evolutionary legacy Proximate and Ultimate Explanations Proximate explanation addresses how things work ( ie. How diseases work or how body combats diseases) -describes function of a trait, its anatomy, physiology, biochemistry, and development from genetic instructions provided by a bit of DNA in the fertilized egg to the adult individu(ie. Proximate account of the taste buds would describe their structure, composition of the tissue and explain how they taste) Ultimate (evolutionary)explanation- addresses why certain things came to be or operate the way they do (in context of disease, may ask why humans, generally, are susceptible to some diseases and not others, or why individual(of same specie) with some traits are more at risk of disease while others are not) ultimate reason humans have evolved a specific trait in first place and why we have DNA that encodes for one kind of structure and not some other -tries to explain what things are and how they got there (evolutionary account of taste buds would explain the advantage of having taste buds ---one way, ask how organisms without taste buds are at disadvantage; another way, ask what ancestral structures were slowly shaped by natural selection to give taste buds present form) Darwinian medicine- new science that discusses disease from an evolutionary perspective 1. Defenses versus Defects -first cause of disease is result of body’s defenses against injury or infection pathogens-things that make you sick -host defenses (fever, pain, nausea, coughing, sneezing) are treated as if they are bodily ‘defects’ that need to be fixed --correcting defect is usually good, but eliminating defense can be dangerous Erect a Barrier: The Skin - skin is first line of defense in protection against mechanical injury, therm(heat)damage, pathogen invasion, and chemical forces (blister is way of protecting wound and speeding up healing process) -protects from bacterial invasion (gets rid of dead outer cells, keeps itself dry, has thing layer of fay or oil, maintains an acidic PH) –be careful not to excessively wash or wash with inappropriate skin care products -Cracked skin without its bacteria-inhibiting oils and acidic pH is vulnerable to infection -proper hand washing is of the utmost importance to prevent the spread of infections, but doing so can often result in dry, chapped hands (wet hands before applying soap, use mild soap and warm water, pat dry, not rub, apply lotion liberally and frequently) Avoid Exposure: Pain and Malaise -pain usually thought of as bad, but can be adaptation that helps us escape or avoid an immediate threat -pain is also adaptive because it contributes to learning by motivating us to avoid harm and protect ourselves from environmental hazards -pain alerts us to danger and motivates us to seek help when there is potential for injury (painful tumors) -pain can evolve to be adaptive (traits evolve within population when individuals that have the trait gain a fitness advantage –able to produce more offspring over their lifetime compared to individuals who do not possess that trait) -rare condition "congenital insensitivity to pain" is when people are born without sense of pain-can cause continuous injury to themselves and often have shorter lifespans Expel Pathogens -many suggest excess nasal discharge is part of body’s inflammatory response to irritation from an invading microorganism (runny nose is defense that may actually help you to expel pathogens) -controversial hypothesis that monthly menstrual cycle is to eliminate pathogens introduced into the female reproductive tract by sperm (proposes sperm, enters uterus after sex, carry bacteria that’s potentially harmful and could be absorbed through walls of the uterus - during menstruation, bacteria is flushed out of body along with lining of the uter–others say menstruation has no adaptive value, but is rather a by-product of the co-evolution of the embryo and mother Defenses Against Natural Toxins -human body has many remarkable defenses against toxins -best defense against toxic substances is avoidance -once toxin is swallowed, stomach acid and digestive enzymes may effectively neutralize it -stomach lining is protected by a mucous layer, and if cells are damaged they quickly regenerate - if toxin’s absorbed into blood system from the stomach, it first passes to the liver -many women get nauseous during first 3 - 4 months of pregnancy when fetus is most vulnerable (women who are not sick often, eat whatever they feel like, and therefore would be exposing their early fetus to harmful levels of food toxins) -Darwinian would hypothesize that nausea during pregnancy would be an adaptive response and would, therefore, predict that women who experience nausea would produce babies that are healthier because they have a lower exposure to toxins -non-adaptive view might hypothesize that being sick throughout pregnancy means that there is something wrong with the woman--would predict that these women would produce babies with lower birth weights than average because they were unable to provide sufficient nutrition -many studies show that women with normal levels of nausea and vomiting of pregnancy (NVP) in fact do have lower rates of miscarriage, there has been little correlation between NVP and any other birth outcomes like birth defects, low birth weight, etc. (very few studies have directly tested the hypothesis) -Brown found no relationship between the intake of vegetables, nausea, and pregnancy outcomes. -Flaxman and Sherman point out possible flaws in the Brown study, to further strengthen their support for the idea that NVP protects the fetus from dietary toxins. Attack Invaders: Fever -numerous studies show adaptive significance of fever -fever is body’s way of fighting infection by a pathogen -Julius Wagner-Jauregg intentionally infected thousands of syphilis patients with malarial parasites - patients that were infected with malarial parasites showed remission rate of about 30%, compared with a remission rate of about 1% of those that did not receive the treatment - awarded the Nobel Prize for “fever therapy.” --treating fevers may prolong illness, as it may interfere with your body’s natural defense (not all fevers are protective, and very high fevers are maladaptive and need to be treated because not only do they deplete your nutrient stores and cause male sterility, very high fevers can cause delirium, seizures, and even permanent tissue damage) Attack Invaders: The Immune System -immune system is the body's defense against pathogens -made up of network of cells, tissues, and organs throughout the body that work together to attack invaders and protect the body - start working when an infectious agent enters the body through injury or through illness -Vaccines are created to help the body combat against infectious diseases (consist of pathogen’s dead or modified microbes, or microbial DNA which trigger an immune response in the body) -different vaccines are prepared to counter different diseases -body’s immune system attacks harmless vaccine, recalls the intruder and prepares for invasions against future attacks- person becomes immunized against the infectious disease - despite all the positive effects of vaccines, there are people that argue vaccines are unnecessary and dangerous because they cause neurological disorders like autism -think vaccines benefit hugely powerful and profitable drug companies and not general public 2. Pathogens: Bacteria, Viruses, and Prions -second cause of disease occurs when host is infected by a pathogen Pathogens- microorganisms (bacteria, viruses, or priothat cause disease by infecting a host bacteria (bacteria is plural and bacterium is singulliving, one-celled, “round, spiral, or rod-shaped single- celled microorganisms that live in soil, water, organic matter, or the bodies of plants and animals, and that are usually autotrophic, saprophytic, or parasitic in nutrition - many are benign or helpful, many cause illnesses (pneumonia, strep throat, food poisoning, tetanus, botulism, salmonella, typhoid, and leprosy) Viruses- very small (much smaller than bacteria)and can contain either DNA or RNA -Responsible for diseases such as rabies, smallpox, poliomyelitis, hepatitis, influenza, the common cold, measles, mumps, chickenpox, herpes, rubella, hemorrhagic fevers, and the acquired immunodeficiency syndrome (AIDS) -Unlike most other life-forms, viruses require a suitable cell to invade in order to reproduce -considerable debate in the scientific literature over whether viruses are living organisms or not -they are "life-like" in having DNA and an organized structure, but viruses cannot reproduce on their own and they do not have cell-like features Prions-abnormal proteins that infect cells and cause normal prion proteins in the brain to fold abnormally -result in brain damage and cause fatal dementia-like diseases in people and animals -prion diseases include Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy (BSE or mad cow disease) in cattle -Stanley Prusiner proposed idea that proteins could be infectious agents (his ideas were severely criticized because proteins were never thought of as pathogens, but finally in 1997 he received a Nobel Prize for the discovery of prions) The Host-Pathogen Arms Race -hosts have developed strategies to prevent invasion and minimize the impact of pathogen invasion, the pathogens have adapted counter-strategies - pathogens and hosts are in a never-ending state of war --continual process of co-evolution between a pathogen and its host. -variety of pathogen counter-defenses can be generally classified into two categories Categories of pathogen counter-defenses: Be Sneaky! Be Ruthless! Get inside Attack host defenses Avoid detection Reproduce Manipulate host & find new "victims" -cost of maintaining defenses could be enormous to the organism, but the cost of losing could be so great that there is no choice but to maintain them -arms race is really a very complicated co-evolutionary process, involving the merger, union, and re- emergence of new species. -evolution consists entirely of trial-and-error tinkering-- process is slow and unguided-in some ways misguided-but there is no limit to the precision and complexity of adaptation that the Darwinian process can generate Nesse and Williams- “Bacteria can evolve as much in a day as we can in a thousand years, and this gives us a grossly unfair handicap in the arms race" -one explanation of how we manage to survive most infections is -- we can alter ratio of various antibody- producing cellsto maximize our defenses (if you had mumps as a child, you are immune to this infection as an adult because you carry around a higher level of lymphocytes that make the antibodies to this specific pathogen. Anytime you encounter mumps as an adult, your immune system responds rapidly and there is no re-infection) -most cases, immune system prevents the reoccurrence of childhood diseases -chicken pox is exception to this rule---unusual virus as it remains latent in body and can return later in life -during a childhood, virus ascends nerve cells and stays there in a dormant state until recovery, when the virus is then eliminated from the rest of the body. Later in life, the body's immunity to chicken pox virus may weaken, and in some people, the virus can descend the nerve cells and reappear as shingles, vesicles which appear on the skin surface at the base of the nerve The Evolution of Virulence -pathogens with severe effects are called virulent (those causing tuberculosis or AIDS can be lethal) -other pathogens can be rather benign, such as those causing the symptoms of the common cold -Three factors influence the level of virulence of a pathogen: 1. Mode of Transmission :If illness of a host significantly impairs transmission, then parasites should evolve to have milder effects(rhino virus that causes common cold has interest to avoid making you really sick, otherwise you would stay home in bed and not come in contact with potential new hosts or victims) - person's movement improves transmission of the virus -if pathogen is transmitted by a vector (e.g., a biting insectthen incapacitation of the host will not affect transmission rates
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