BISC 307L 1st Edition Lecture 1 Current Lecture What is evolution Descent with modification Outcome is an organism matched to its environment o Matching during evolution optimizes reproductive success Matching optimizes REPRODUCTIVE success o Called FITNESS the probability that one s genes will be passed on to the next generation o Results within a population optimizes the average fitness within a particular environment o Will not optimize life span Evolution does not optimize lifespan or general health Natural selection is driving force Mechanisms of evolution Darwin s observations 1 Species produce more offspring than the environment can support 2 There is always variation within a population with the ability to compete for resources survive and reproduce 3 Some variation is inherited o Due to 3 sources 1 Mutations 2 Recombinations 3 Epigenetic modifications 4 Developmental Plasticity environment affects phenotype during development and also nervous system Because of these observations 4 Differences that produce offspring in more successful forms will be more prevalent natural selection 5 Selection will lead to change in the population evolution micro or macro Natural Selection is NOT equal to survival of the fittest Selection maximizes reproductive fitness not health or longevity o Cant apply these principles to social aspects of life o ONLY REPRODUCTIVE FITNESS o Survival of genes not survival of health or well being Evolutionary success of humans does not require long life o Before people did not live long enough to contract the diseases we contract now o Historical life span of humans makes sense if we look at human fertility with age o Puberty is happening earlier and earlier o Reproductive health peaks in 20 s o Reproductive disease affects people in their 20s Natural selection therefore optimizes things that occur during reproductive life only Heart Failure if our body is such a great system why is it designed to blow up Because disease of middle and advanced life These mechanisms work well in young reproductive people Examples of Evolutionary Flaws Humans are bipedal and have large brains o Evolution results in compromises Bipedalism requires narrow pelvis vs newborn survival requiring large head Narrow pelvis is not good for reproduction Big brain means babies head is big Babies are altricial meaning they need extended parental care We are unusual because we stand up and have large brains o Why is this important None of our ancestors are bipedal Our spine has a curve and is weak We are topheavy too much weight on legs We need assistance for birth Human babies must rotate in womb and be in right position to fit through birth canal Success rate of human birth is 85 without assistance o So why are we like this Early moms probably did not get help with giving birth but we find ways to get around this Evolution is about compromise human pelvis is as wide as it can be to allow for walking and running and for a baby s head Large brain size head cannot be fully developed at birth brains born immature don t mature until 30yrs old As a result women don t have very many babies we are inhibited to have too many babies Human body is full of Design Flaws 1 Why the appendix o Has no known function but was probably used as a pouch to help digest food o We cannot modify cant start over 2 Can t synthesize vitamin C o Probably because our ancestors ate a lot of fruit 3 Inside out retina o light has to pass through everything else to get to the light sensitive cells and then the light is distorted o makes sense in evolutionary terms because nerves and blood vessels supply from the outside 4 Crossing of trachea and esophagus o we can choke and get lung infections pretty easily o probably evolved from lung fish Why Do We Get Sick Proximate Reasons Pathophysiology examples o Hypertension is due to an increase in vascular resistance o Sickle cell anemia is due to mutation in hemoglobin gene o Cerebral palsy is due to asphyxia during birth o Cystic fibrosis is due to mutation in chloride channel gene Ultimate Reasons Evolutionary Medicine approach o Four reasons for why we are vulnerable 1 Fitness is not about health and wellbeing 2 Constraints and tradeoffs are inevitable 3 Human evolution is too slow to cope with challenges of changing environment First change in environment was slow so evolution worked but then the environment started changing faster The last 10000 years have shown a lot happening topographically Can lead to mismatching between human adaptations and challenges of the environment Ex lactose intolerance Human evolution much slower than pathogen evolutiondrug resistance 4 Our evolved defenses may be harmful or seem harmful Evolution has given us powerful immune defenses but excessive reactions cause harm Fever can cause seizures brain damage Allergies asthma anaphylaxis Autoimmune disease Why weren t these diseases eliminated The immune system is complicated The environment during early life can shape the development of the immune system developmental plasticity Clues 1 In developing countries early malnutrition results in more susceptibility to disease later in life 2 In Sweden the infectious diseases have dropped due to improved health care and hygiene Hygiene Hypothesis Explains why chronic disease is increasing Found that incidence of chronic disease higher in those who are raised in hygienic cities as opposed to farms This suggests that in order for the immune system to develop its regulatory mechanisms it needs to undergo certain exposures during development Without being challenged by normal pathogens the immune system doesn t develop its full regulatory path