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Lecture 5

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University of Toronto St. George
Dan Sellen

Lecture 5 Overview Major themes in evolutionary medicine Fitness / tradeoffs / coevolution Levels of explanation Types of hypotheses Life history theory Human life history Links to sociality Adaptation Vulnerability Core Concepts • COEVOLUTION ◦ Humans as a "multi-species assemblage" with prey + pathogens ◦ Humans evolved in relation to other species • Evolutionary ecology: medically relevant examples ◦ pathogen evolution: HIV in response to ART (antiretroviral therapy); an- nual vaccines for influenza strains' antibiotic resistant bacteria ■ human immune response also evolutionarily relevant: producing antigens ■ anti-viral, anti-biotic therapies do not work for long as pathogens evolve to become resistant to them ■ co-evolutionary "arms race" ◦ cancer: neoplasia (abnormal tissue growth) progression, resistance to chemotherapy ◦ human ecology: technological and social changes can increase, re-dis- tribute or fundamentally change disease risk ■ technological changes have brought health benefits to some popu- lations, but changes in food production, rise of capitalism, etc. have affected people's health socially, politically, economically, environ- mentally ◦ recent rapid environmental change: new threats, mismatch of people and environments ■ pushing humans into environments they did not evolve in ■ Mismatch with modern environments: NUTRITION of Hypothesized Ancestors vs Contemporary Americans ■ source: Trevathan, W.R. (2007). "Evolutionary medicine." Annual Review of Anthropology. Lecture 5 ■ hypothesized ancestors had greater percentage of calories from protein, less in fat, more in fibre, less sodium, more cal- cium ■ what are the effects of indoor vs outdoor life (natural vs, electric lighting), living in social groups larger than 100-150 persons, animal husbandry and agriculture, human modifica- tion of environmental services, etc.? • TRADEOFFS ◦ As for all organisms, humans cannot be perfect at everything • Selection produces tradeoffs in traits under different constraints ◦ physical: neonatal head size versus maternal pelvic size ■ large brained babies (selective advantage) vs narrow hips (trait of bipedalism) ■ thus babies go through greater amount of postnatal growth in brain size compared to other animals, in addition to brain growth during pregnancy ■ bipedalism evolved before increased brain growth - tradeoffs driv- ing the order of things ◦ reproductive: numbers versus survival/success of children ■ for any organism, parental investment is required to ensure survival of offspring ■ organisms that cannot protect their offspring will have many off- spring; ex. salmon, semelparity vs iteroparity (humans) ◦ development: wasting versus standing versus brain growth; low birth weight, SGA (small for gestational age); fetal origins of adult disease ■ human babies do not stunt brain growth in order to maintain growth in weight and height; cognitive abilities more important for humans ■ low birth weight caused by inadequate nutrition for mother but can be made up for in postnatal feeding ■ preterm, small gestational age, low birth rate = always at higher risk of illness and disease for rest of their life ◦ life history: early investment in reproduction vs later investment in repair + maintenance (senescence/aging) ■ reproducing early in life can detract from maintaining your own health ■ reproducing early and often can result in shorter life expectancy ■ some describe senescence as damage from reproduction • Functional design of human organ development ◦ Percent of Total Postnatal Growth vs Age (M. De Gludice et al, Develop- ment Review) ■ Brain - infant prioritizes, mother willing to provide nutrients ■ Lymphoid: goes beyond 100% - immune system grows rapidly be- tween childhood and juvenile ■ Dentition: must develop to allow for eating, to grow body ■ Body: initially faster growth than dentition ■ Reproductive Lecture 5 • Immune response: costs + benefits for survival + reproduction (Lynn B. Martin, In- fection Protection and Natural Selection) ◦ there is a tradeoff between activity of immune response, which costs ener- gy, and suppresses certain hormones involved in reproduction ◦ for any mammal, mother must down regulate immune system to allow for carrying fetus Levels of Explanation • Source: Nesse, R.M. & Stearns, Evolutionary Applications • Tinbergen's fou
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