Lecture 19 - Intorduction to evolutionary medicine

evolutionary medicine

applications of evolutionary principles to the problems in health and disease

evolutionary medicine approach

diseases need both proximate explanations for underlying mechanisms as well as ultimate explanations of whyc any vulnerabilities exist

why might we be vulnerable to disease?

tradeoffs, natural selection acts to increase the reproductive success of genes regardless of health, some signs of disease are defenses, mismatch with current environments and pathogens are evolving quicker than we are

DNA repair tradeoff

beneficial for promoting longevity but costly for fecundity

immune defense tradeoff

beneficial because it targets pathogens but might also target it self which is a cost

beneficial trait evolution (case 1)

trait was beneficial in the past environment so it increase in frequency cause it was selected on but in the current environment the trait leads to vulnerability to disease

neutral trait evolution (case 2)

trait was neutral in the past environment so it was maintained in the population but in the current environment the trait leads to vulnerability to disease

pathogens

infectious disease caused by organisms that can also evolve and have benefits of living short time than humans can evolve

characteristics of pathogens

faster generation times, large population sizes and high mutation rates cause they are highly variable which means more adaptations evolve than counter ones

how to test if signs of disease may actually be defenses?

quantify the costs and benefits of the trait to both the individual and the pathogens

fever

elevated body temperature in response to pathogen infection

if a fever is a direct effect of pathogen replication in a host what do we expect will happen?

pathogen success increase with fever (disease)

if a fever is an adaptive defense against the pathogen what do we expect will happen?

pathogen success decrease with fever (defense)

behavioural thermal regulation in a iguanas

they are ectotherms so they behaviourally regulate their body temperatures and so when they are injected with bacteria they elevate their body temperatures inducing a fever like response

iguana adaptive value of fever experiment

they were infected with a bacterial pathogen then held at different temperatures and prevented from behaviorally regulating their body temperature

iguana experiment results

found that survival was best for them when temperatures were held at fever level

fever regulation response in humans experiment

individuals were infected with rhinovirus and tests for effectiveness of anti fever treatment in reducing other fever symptoms

fever regulation human experiment results

found that symptoms were worse in individuals that were given fever reducing medicine

mismatch environments study

approach was to compare outcomes in modern populations with populations living in environments that more closely resemble evolutionary ancestors

myopia

near sightedness, so objects are out of focus caused by elongated eye, genetic basis for it

• frequency has been increasing

why is myopia increasing?

because genes that give rise to myopia now did not cause myopia in our past environment like modern lifestyle including more reading under artificial light so less time spent outdoors

myopia study

individuals froma population with a recent shift in lifestyle were studies and found that myopia was more frequent in younger groups cause they grew up in a modern environment

myopia prevalence explanation

suggestion that while it has a genetic basis the phenotype is plastic so only in certain environments will those genes result in myopia

what is the key environmental influence responsible in the onset of myopia

exposure to natural light in early development cause this increased dopamine which stops the eye from over elongating

emmetropic eye

normal eye

hyperopic eye

shortened eye, far sighted