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1 Novel environments

Human Adaptation - ad aptos : ‘good fit’ between trait and environment -produced by natural selection -better than alternatives in immediate circumstances How are health and disease related to human adaptations? The BIG 8 can give rise to apparent maladaptations. 1 Novel environments

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1 Novel environments

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  1. Human Adaptation - ad aptos: ‘good fit’ between trait and environment -produced by natural selection -better than alternatives in immediate circumstances How are health and disease related to human adaptations? The BIG 8 can give rise to apparent maladaptations 1 Novel environments 2 ‘Novel’ genes, genotypes (via mutation, drift, inbreeding, gene flow,selection) 3 Tradeoffs between opposingselective pressures (eg autoimmune vs infectious diseases) 4 Extremes of adaptations (eg overgrowth, extreme male brain) 5 Conflicts within and between species 6 Constraints on optimization (evolutionary legacies) Trait involves benefitsto own reproduction, or to kin, that offset costs to phenotype (genes that increase reproduction spread even if they decrease health, happiness or longevity) 8 Trait is not a disease but a beneficial protective response (eg cough,fever,pain,nausea,vomiting,anxiety,fatigue)

  2. Definitions and perspectives on adaptation (from Crespi 2000) Teleonomic - focus on functional design - how the trait or form of trait has been ‘designed’ by selection for function in some context (2) Phylogenetic - infer origin of trait using phylogeny, infer ‘selective regime’ under which trait arose, test performance of trait in ancestral and current selective regimes. If trait arose under current selective regime, & exhibits higher performance than antecedent, then is called an adaptation; most generally, this approach is the comparative method (3) Population and quantitative genetic - relate allelic and genotypic variation to phenotypic variation and fitness variation. ‘Purifying’ selection and stabilizing selection are evidence of adaptation, positive and directional selection are evidence for adapting. Adaptive peak viewpoint is conceptually useful Fitness Trait value

  3. Observe a Trait, Trait Variation (cognitive, emotional,behavioral, morphological, physiological, molecular) What is its adaptive significance? -> does presence or form of trait or phenotype increase survival and reproduction of its bearers, and if so, how? -> does trait involve interactions between individuals, within or between species? Cooperation or conflict? Information on adaptive significance is crucial to understanding both proximate and ultimate causes of the forms of traits NOTE: adaptive significance is often conditional on environmental variation

  4. ALTERNATIVE HYPOTHESES *(1) Adaptive (function optimal) Very close fit between trait and environment of trait *(2) Adaptive compromise Tradeoff between opposing selective pressures - what are they? costs AND benefits present *(3) Non-adaptive (neutral) byproduct of another trait, or other cause *(4) Mal-adaptive HOW DO WE TELL THE DIFFERENCE?

  5. APPROACHES (1) Functional design what does trait do? with what aspect of environment does it interact? (2) Analysis of selection measure genotype or phenotype, and fitness, and analyze their relationship (3) Phylogenetic and comparative analysis analyze relationship between traits, or traits and environments, over evolutionary time, across species or across populations, in a phylogenetic context

  6. METHODS OBSERVATION What are processes and patterns in nature? Correlation vs causation: x,y, and z given x <-> y, causal relation is: x-> y or y-> x or z -> x and y EXPERIMENTS Perturb the system, predict the outcome based on hypothesis under test, differentiate between correlation and causation - KO MODELLING Make assumptions, explore mathematical consequences Components: (1) strategy set (2) optimization criterion (eg fitness) (3) maths for determining which ‘strategy’ is optimal under what circumstances

  7. Combining the approaches and methods (1) Functional design Observation, experiments, modelling: what aspect of environment does trait interact with, and how? (2) Measuring selection and response to selection Observation: how does trait covary with components of fitness? What is the form of selection? Is the trait evolving now? What is its genetic basis? (3) Comparative, phylogenetic method Observation: How have trait and environment changed over evolutionary time? Has the trait evolved in parallel with the environmental factor? Have two traits evolved in association with one another? Can do between species or between populations.

  8. Phylogenetic, comparative tests of evolutionary theories • EXAMPLE: more sperm competition should select for larger testes (and more sperm) • Experimental evolution: often not practical • Interspecific comparison: test whether traits are correlated across species • Problem: related species may share the same traits due to shared ancestry = phylogenetic non-independence • Result is that species cannot be taken as independent data points

  9. Example F E D Testes size C B A Degree of sperm competition

  10. Plain correlation doesn’t mean much – if species D, E and F are closely related they could have evolved larger testes sizes only once

  11. Independent contrasts Felsenstein 1985, 1988 Trait 1: (6-5=1) Trait 2: (2-1=1)contrast: (1,1) 5 1 6 2 6 2 9 5 Trait 2 Contrast Trait 1 Contrast Felsenstein 1985

  12. Independent contrasts Trait 1: (9-6=3) Trait 2: (5-2=3) contrast: (3,3) 5 1 6 2 6 2 9 5 Trait 2 Contrast Trait 1 Contrast

  13. Independent contrasts Trait 1: 7.5-5.5=2 Trait 2: 3.5-1.5=2 contrast: (2,2) 5 1 6 2 6 2 9 5 Average of descendents 5.5 1.5 7.5 3.5 Trait 2 Contrast Trait 1 Contrast

  14. SOME CAUSES OF LACK OF ADAPTATION (1) Evolutionarily-novel environments (mismatches!) e. g., moths at lights, humans with novel technology, candy bars (2) Time lags e. g., fruit dispersal by extinct megafauna, rapid change in human environments, long time needed to fix advantageous mutations; LCT (3) Genetics Lack of sufficient genetic variation Heterozygote advantage Linkage, pleiotropy (4) Local, not global, optimization

  15. Case study: laryngeal nerve Laryngeal nerve anatomy 1. down the neck 4. to larynx 2. behind the aorta 3. up neck Is it adaptive? For giraffes?

  16. EXAMPLES OF ANALYSES OF ADAPTATION Darwin’s finches Human brain size Recognizing and demonstrating maladaption is challenging and it is best conducted by combining analyses of proximate mechanisms AND ultimate causes

  17. Darwin’s finches

  18. Beaks as functionally-designed ‘tools’ for food acquisition

  19. Measuring selection on beak size

  20. Phylogenetics of finches and their beaks No comparative analyses done yet!

  21. EXAMPLES Darwin’s finches Human brain size (and shape) FUNCTIONAL DESIGN MEASUREMENT OF SELECTION COMPARATIVE ANALYSIS

  22. FUNCTIONAL DESIGN OF THE BRAIN: ‘Social Brain’: Distributed, Integrated Neural System ‘for’ Acquiring and Processing Social Information Gaze detection Mentalizing Funct IMAGING LESIONS TMS Natural variation Social judgement Facial perception Affect recognition

  23. SELECTION AND HERITABILITY: Human brain size increase: Tripled in about 4 million years Mainly in the neocortex Selection on genes ‘for’ human brain size Microcephaly genes ASPM and MCPH1 Heritability of brain size is high

  24. BENEFITS: BRAIN SIZE IS POSITIVELY CORRELATED WITH MEASURES OF ‘INTELLIGENCE’, AMONG PRIMATES and WITHIN HUMANS Brain, 2006 Brain Behavior Evolution, 2007 p<0.01 Narr et al. Cerebral Cortex, 2007 p<0.01

  25. When and how has most natural selection taken place in humans? Now EARLY LIFE -Malnutrition -Pathogens -Infectious diseases %SV AGE Austria, Upper Paleolithic

  26. In humans, maternal ‘intelligence’ is positively correlated with measures of child survivorship and health Sandiford et al. 1997 Martin & Kubzansky 2005 Wachs et al. 2006 Cvorovis et al. 2008 Webb, Sellen et al. 2009 Implications for public health?

  27. COSTS Brain is VERY LARGE and energetically COSTLY to grow and maintain: Is 3X larger than expected for primate body size Has 22X the metabolic rate of skeletal muscle

  28. PHYLOGENETIC, COMPARATIVE ANALYSIS OF BRAIN FUNCTION 1996 2007

  29. Human Adaptation - ad aptos: ‘good fit’ between trait and environment -produced by natural selection -better than alternatives in immediate circumstances How are health and disease related to human adaptations? The BIG 8 can give rise to apparent maladaptations 1 Novel environments 2 ‘Novel’ genes, genotypes (via mutation, drift, inbreeding, gene flow,selection) 3 Tradeoffs between opposing selective pressures 4 Extremes of adaptations (eg overgrowth, extreme male brain) 5 Conflicts within and between species 6 Constraints on optimization (evolutionary legacies) Trait involves benefitsto own reproduction, or to kin, that offset costs to phenotype (genes that increase reproduction spread even if they decrease health, happiness or longevity) 8 Trait is not a disease but a beneficial protective response (eg cough,fever,pain,nausea,vomiting,anxiety,fatigue)

  30. Genes ultimately mediate medically-important tradeoffs I TP53 Codon 72: Pro/Pro compared to Pro/Arg, Arg/Arg Lower apoptotic potential, leading to Higher implantation failure (& lower reproduction) Higher cancer risk Higher overall survival (longevity) Other polymorphic genes in TP53 pathway mediate same tradeoffs p53 is a nuclear phospho-protein which, in response to DNA damage, slows progression through the cell cycle and initiates apoptosis if damage is severe. Tumour-specific point mutations occur in many forms of human cancer with as many as 50% of cancers containing a p53 mutation. 20% of mutations are concentrated at 5 'hot-spot' codons. Functional design? knockouts, molecular mechanisms Selection - at molecular level Comparative - within/among species variation Kang et al. 2009 PNAS; Corbo et al. 2012 PLoS ONE

  31. Genes ultimately mediate medically-important tradeoffs II APOE E4 alleles, compared to E3and E2 Better verbal, memory skills (especially when young) Increased risk of schizophrenia and Alzheimer’s Alexander et al 2007 Biol Psy; Chang et al. 2011 Neuromage Jochemsen et al. 2012 Neurob. Aging

  32. Genes ultimately mediate medically-important tradeoffs III COMT VAL158METpolymorphism Mediates prefrontal, striatal dopamine levels VAL - better cognitive flexibility, updating; worse cognitive stability MET - worse cognitive flexibility, updating; better cognitive stability Fallon et al. 2012 Cerebral Cortex

  33. Combining the approaches and methods to recognize adaptation (e.g., health) and maladaptation (e. g. disease and its risk) (1) Functional design Observation, experiments, modelling: what aspect of environment does trait interact with, and how? (2) Measuring selection and response to selection Observation: how does trait covary with components of fitness? What is the form of selection? Is the trait evolving now? What is its genetic basis? (3) Comparative, phylogenetic method Observation: how have trait and environment changed over evolutionary time? Has the trait evolved in parallel with the environmental factor? Have two traits evolved in association with one another? Can do between species or between populations.

  34. Causes, effects and evolution of allelic variation: how to THINK about genes and genic variation, and their relation to disease Inclusive fitness: how to THINK about situations where related individuals interact Adaptive significance: how to THINK about variation in phenotypes - benefits and costs, tradeoffs, evolutionary history, relation to maladaptation/disease NOW How to THINK about patterns of evolutionary change across generations in genes and phenotypes -> phylogenetics, the history of biological entities

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