Human Adaptation - ad aptos: good fit between trait and environment

Transcription

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 Novel environments Novel genes, genotypes (via mutation, drift, inbreeding, gene flow,selection) 3 Tradeoffs between opposing selective pressures (eg autoimmune vs infectious diseases) 4 Extremes of adaptations (eg overgrowth, extreme male brain) Conflicts within and between species Constraints on optimization (evolutionary legacies) 7 Trait involves benefits to 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) Definitions and perspectives on adaptation (from Crespi 000) () Teleonomic - focus on functional design - how the trait or form of trait has been designed by selection for function in some context () 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 Fitness evidence for adapting. Adaptive peak viewpoint is conceptually useful Trait value 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 ALTERNATIVE HYPOTHESES *() Adaptive (function optimal) Very close fit between trait and environment of trait *() 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? APPROACHES () Functional design what does trait do? with what aspect of environment does it interact? () 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

2 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: () strategy set () optimization criterion (eg fitness) (3) maths for determining which strategy is optimal under what circumstances Combining the approaches and methods () Functional design Observation, experiments, modelling: what aspect of environment does trait interact with, and how? () 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. 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 Testes size A C Example B E D Degree of sperm competition F Plain correlation doesn t mean much if species D, E and F are closely related they could have evolved larger testes sizes only once Independent contrasts 9 Felsenstein 98, 988 Trait : (-=) Trait : (-=) contrast: (,) Trait Contrast Felsenstein 98 Trait Contrast

3 Independent contrasts Independent contrasts 9 Trait : (9-=3) Trait : (-=3) contrast: (3,3) 9 Trait : 7.-.= Trait : 3.-.= contrast: (,) Trait Contrast.. Average of descendents Trait Contrast Trait Contrast Trait Contrast SOME CAUSES OF LACK OF ADAPTATION () Evolutionarily-novel environments (mismatches!) e. g., moths at lights, humans with novel technology, candy bars () 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 4. to larynx 3. up neck Case study: laryngeal nerve Laryngeal nerve anatomy. down the neck. behind the aorta Is it adaptive? For giraffes? EXAMPLES OF ANALYSES OF ADAPTATION Darwin s finches 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 3

4 Beaks as functionally-designed tools for food acquisition Measuring selection on beak size Phylogenetics of finches and their beaks EXAMPLES Darwin s finches Human brain size (and shape) FUNCTIONAL DESIGN MEASUREMENT OF SELECTION COMPARATIVE ANALYSIS No comparative analyses done yet! Gaze detection FUNCTIONAL DESIGN OF THE BRAIN: Social Brain : Distributed, Integrated Neural System for Acquiring and Processing Social Information Mentalizing Facial perception Affect recognition Social judgement Funct IMAGING LESIONS TMS Natural variation 4

5 BENEFITS: BRAIN SIZE IS POSITIVELY CORRELATED WITH MEASURES OF INTELLIGENCE, AMONG PRIMATES and WITHIN HUMANS SELECTION AND HERITABILITY: Human brain size increase: Tripled in about 4 million years Mainly in the neocortex Brain, 00 Selection on genes for human brain size Microcephaly genes ASPM and MCPH Brain Behavior Evolution, 007 Heritability of brain size is high p<0.0 Narr et al. Cerebral Cortex, 007 p<0.0 When and how has most natural selection taken place in humans? EARLY LIFE -Malnutrition -Pathogens -Infectious diseases Now In humans, maternal intelligence is positively correlated with measures of child survivorship and health Sandiford et al. 997 Martin & Kubzansky 00 Wachs et al. 00 %SV Austria, Upper Paleolithic Cvorovis et al. 008 Webb, Sellen et al. 009 AGE Implications for public health? COSTS Brain is VERY LARGE and energetically COSTLY to grow and maintain: PHYLOGENETIC, COMPARATIVE ANALYSIS OF BRAIN FUNCTION Is 3X larger than expected for primate body size Has X the metabolic rate of skeletal muscle

6 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 Novel environments 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) Conflicts within and between species Constraints on optimization (evolutionary legacies) 7 Trait involves benefits to 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) Genes ultimately mediate medically-important tradeoffs I TP3 p3 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 0% of cancers containing a p3 mutation. 0% of mutations are concentrated at 'hot-spot' codons. Codon 7: 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 TP3 pathway mediate same tradeoffs Functional design? knockouts, molecular mechanisms Selection - at molecular level Kang et al. 009 PNAS; Comparative - within/among species variation Corbo et al. 0 PLoS ONE Genes ultimately mediate medically-important tradeoffs II APOE E4 alleles, compared to E3 and E Genes ultimately mediate medically-important tradeoffs III COMT VAL8MET polymorphism Mediates prefrontal, striatal dopamine levels Better verbal, memory skills (especially when young) Increased risk of schizophrenia and Alzheimer s VAL - better cognitive flexibility, updating; worse cognitive stability MET - worse cognitive flexibility, updating; better cognitive stability Alexander et al 007 Biol Psy; Chang et al. 0 Neuromage Jochemsen et al. 0 Neurob. Aging Fallon et al. 0 Cerebral Cortex Combining the approaches and methods to recognize adaptation (e.g., health) and maladaptation (e. g. disease and its risk) () Functional design Observation, experiments, modelling: what aspect of environment does trait interact with, and how? () 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. 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