Evolution and Membrane Dynamics

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Evolution and Membrane Dynamics

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University of Southern California
Bisc 307l - General Physiology
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BISC 307L 2nd Edition Lecture 2 Current Lecture Why do we get sick? There are 2 ways to analyze this question: 1. Proximate Reasons (Pathophysiology). The traditional way, looking at the immediate cause of the disease (the way doctors do). Examples: • Hypertension is due to an increase in vascular resistance • Sickle cell anemia is due to mutation in hemoglobin gene • Cerebral palsy is due to asphyxia during birth • Cystic fibrosis is due to mutation in chloride channel gene 2. Ultimate Reasons (Evolutionary Medicine). This is a new approach, asks “Why has evolution left our bodies vulnerable to disease?” The first formulations of people in this field resulted in the following four points: 1. Selection is about fitness, not health, well-being, or strength. 2. Constraints and trade-offs are inevitable. Evolution only works on pre-existing things, resulting in evolutionary “holdovers”. (term often used for this is “BISLAGIATT” - but it seemed like a good idea at the time). 3. Human evolution is too slow to cope with challenges, especially the challenges of a changing environment. 4. Our evolved defenses may be harmful or seem harmful Evolution is too slow to cope Evolution can only optimize within an environment. Figure on right graphs time from 9k years BC to 2000, showing population of earth in millions. Shows that the change in environment was relatively slow, up until the agricultural revolution, when human population took off. But while environmental changes have been rapid, our human evolutionary change has been relatively slower. This has lead to mismatches between human adaptations and the challenges of our environment. Example 1: lactose intolerance. All babies can digest lactose, but after childhood, there is repression of the lactase gene because early on in human history, we accumulated mutations to make it nonfunctional. But with the advent of domestication of animals, there were secondary mutations that inactivated the repressor of the lactase gene, so it continued to be expressed. Example 2: food availability and food storage. In the past, to survive, we had to evolve the ability to take advantage of food when it was available and convert it to stored fat as insurance against the next period of starvation. Now there’s a mismatch – high calorie foods and low activity lifestyle conflict with our ability to efficiently store fat. Evolved Defenses May Be Harmful Evolution has left us susceptible to disease in that our evolved defenses may be harmful. It has given us powerful immune defenses, but excessive reactions can cause harm: • Fever (pyrexia) can cause seizures, brain damage • Allergies (inappropriate immune reaction), asthma, anaphylaxis • Autoimmune disease (long list of disease in which the immune system inappropriately attacks tissues of your own body) Immune system, like the central nervous system, experiences developmental plasticity (the environment during early life could shape the development of the immune system). • Example: In undeveloped countries where people experience malnutrition at an early age, even after overcoming this problem, these individuals are much more susceptible to disease ...

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