Lecture Notes on Evolutionary Medicine PDF

 August 30 Friday Evolutionary medicine: The field at the intersection of evolution and medicine uses the evolutionary theory to understand why humans get sick Proximate explanations: (The how explanation)...

 August 30 Friday Evolutionary medicine: The field at the intersection of evolution and medicine uses the evolutionary theory to understand why humans get sick Proximate explanations: (The how explanation) Explains how the body works answers what and how questions about structure or mechanism that is actually causing the disease. most medical research looks for proximate explanations. Ex: constantly gets flat tires; proximate explanation = I get on rough roads that have a lot of holes on them so therefore I get flat tires. Ultimate/evolutionary explanations: (the why explanation) Answers why questions about origins and functions. answers bigger broader questions compared to proximate explanations. Ex: car constantly gets flat tires; Ultimate/evolutionary explanation = the town I live in has a lot of holes in the streets and they don't fix the roads so therefore I fall into the holes and cause the times to go flat. More examples of proximate vs ultimate evolutionary explanations: Taste buds - Proximate explanation: how do we taste? Ultimate/evolutionary explanation: why do we taste? Ultimate/evolutionary explanation examples - A condition or medical issue may be... Part of the body's evolved response to a problem Ex: fever Due to how genes evolve Genes code for proteins → hemoglobin is a protein that carries oxygen and is fund in our blood cells 2 versions of hemoglobin: health vs sickle-cell anemia  Are homozygous recessive → meaning they have geno copies of the sickle-cell allele carrier of allele cone normal gene a one sick gene) Due to design compromises Ex: lower back pain body was designed to walk on 4 legs body evolutionized to a legs later on. our spines: → as we age we will experience lower back pain because we were suppose to be quadrupedal and not bipedal Due to evolutionary legacies Ex: choking The stutters the became the trachea The human trachea (transport air to our lungs) is located in front of the esophagus because a long time ago during the evolution of vertebrates, was positioned next to the structure that became our esophagus. The epiglottis covers or tracks areas but this design wasn't the best, therefore we are stuck with this design Due to the endless evolutionary arms race bet ween bacteria/viruses and hosts → evolutionary arms race: our bodies evolve new defenses to protect ourselves; viruses and bacteria evolve new way to reproduce in our body Due to evolutionary mismatch → evolutionary mismatch: environmental conditions of today are different from the environmental conditions we evolved in. → ways environmental conditions differ?  There is a lot of contamination (pollution, radiation) food: back then we had to hunt for food; now food is very processed water back then wasn't purified like it is now stress: increase of stress because of capitalism ( having to buy food and water for instance Why should we care about evolutionary explanations? Potential contributions of evolutionary medicine: Guide to biomedical research (guide hypothesis) aid in clinical practice Ex: help find out how cancer cells evolve Significant Public Health and policy implications → understand evolution of viruses if we will try to prevent a sickness  September 3 Tuesday Evolution: change in the gene frequency of a population overtime. Forces of evolution: Natural selection - individuals with specific genotypes are more likely than other genotype to ser ve and reproduce; pass on their alleles to the next generation Phenotype: physical expression of genes Adaptation: attribute that is improving the organisms evolutionary fitness Ex: brown beetles are able to camouflage and sur vive compared to green beetles Mutation - a mistake that occurs during DNA replication and one or more nucleotides are substituted for another nucleotide or deleted all together (Nucleotides are the building blocks of DNA) Classifications of mutations as advantageous, neutral, and deleterious is an oversimplification. * more of a continuum A mutation must be present in the gametes (ovum or sperm) is in order to influence evolution Q: Why is mutation considered a force of evolution? There is a change in genotype and if it is being inherited to the next generation then this is considered a force of evolution. Genetic drift - refers to how allele frequencies will change over time in a population due to chance (luck). An example of neutral evolution : all other forces that doesn't have to do with natural selection change in the frequency of a gene variant Ina population due to random sampling of organisms. * large population size → weak effect on gene * small population size → strong effect on gene frequencies  Gene flow - movement of genes into or out of a population usually due to migration. An example of neutral evolution Gene flow is the exchange of genes bet ween t wo populations overtime Gene flow will lead t wo previously separate groups to be more in their similar to each other in their frequency of alleles Separated by a river over time these population will likely come together and produce offspring that will have Aa alleles and therefore these groups will look more similar Examples of evolution: I go to the gym everyday and get super buff. → Not evolution I spend all day in the sun, causing a mutation in my skin cells → not evolution A group of people serve a nuclear attack and they are exposed to a lot of radiation leading to mutation in egg cells and sperm and the mutations are passed onto their kids. In order for there to be natural selection, there mustbe... 1. Genetic variation - we have to have differences for natural selection to occur. 2. Differential reproduction - one version of the gene must be more likely to be passed on than another version of a gene some of us have to have more offsprings than others higher frequencies than others. Levels of selection: Individual level - Group of chimpanzees → one male outcompetes other males for mates → has more offsprings → has a higher chance to pass on their genes Cellular level - Breast cell tissue → mutation that causes the cell to divide and reproduce and passes on the mutation to daughter cells → tumor is created  Natural selection can be seen at the cellar level, because we have genetic variation (breast cell tissue is different) and we have differential reproduction because the cells are reproducing faster (tumor) than the normal cells. Gene level (Selfish Gene ) - Any genetic adaptation is something that increases the chances that a particular gene will be passed on to the next generation whether it allows the organism to live longer or not benefits the gene itself ex: a gene allows the fish to put double the number of eggs however soon after the fish dies. Group level *contraversial* - Idea that natural selection can act on groups Ex: 2 populations of chimps; 1 group learns to use sticks to get Fitness and Kin selection: Fitness: potential for an individual to survive and reproduce successfully and pass on their genes Direct fitness: potential for an individual to pass on their genes to direct descendants Indirect fitness: potential for an individual to pass on their genes via reproduction of our relatives (ex: brother and sister; brother passes on his genes to his sisters offsprings and vice-versa. Inclusive Fitness: the sum of the direct and indirect fitness Direct fitness t indirect fitness= inclusive fitness ex: Usocial insects are insects where just a queen reproduces and all the sisters help out and make sure the queen reproduces a lot and that the offsprings sur vive and reproduce Niche construction: is when an organism alters their environment orniche in a way to benefit their fitness (niche: environment they are making to live and reproduce) Ecological niche - set of environment conditions with which a species normally interacts and depends on for survival and reproduction. whether or not a trait is adaptive depends on an organisms environment. Culture and natural selection: our culture plays an important role in shaping our behavior as well as our environment, therefore has the potential to influence what is adaptive and lead to natural selection Example 1: hunting animals for meat → lack of access to water/famine/drought → consumption of milk → has gene needed to breakdown lactose → consumption of milk → natural selection of genes that allow individuals to break down lactose and drink milk without experiencing gas and diarrean (lactose intolerance) Microevolution vs. Micro evolution - Microevolution: changes in allele frequencies in a population over time Macroevolution: species that emerge from a single common ancestor (looks at large groups over long periods of time) Speciation: new species being formed; species evolving into other species Reproductive isolation: t wo populations of the same species no longer mate successfully (offspring can not reproduce) Constraints on evolution- Evolution is slow especially in organisms that have long lifespans Can't pass through non-functional, less fit terms on the pathway to adaptation. As our linages evolve different structures in the eyes elated as well. Our structures are constrained in their evolution based on phylogeny; base on how our structures evolve over time.  Limited pool of genetic variation in population. Some traits are robust (not sensitive to environmental conditions;genes are robust as well) Example: multiple copies of the gene in the genome buffered against perturbations in the environment Overall evolution is a non-perfect process ***  September 6 Friday What is a gene? Common definition: A sequence of DNA bases that specifies the order of amino acids in a protein Anatomy of DNA: DNA = deoxyribose nucleic acid Refers to genetic 2 Chains of nucleotides sequences (ATGC) DNA Code: Gene - a sequence of nucleotides that codes for a protein Proteins are made up of amino acids DNA instructions are a triplet of bases Example(s): AGA TAC GCT AAT TCA Code is universal Chromosomes: 46 chromosomes can be divided in 23 homologous pairs Homologous pairs of chromosomes: pair of chromosomes that are similar in size and contain similar genes. Much larger than y People that have xx have much more base pairs Contain different genes Mitochondrial DNA: extra DNA in the mitochondria their own DNA found in the mitochondria important for function of the mitochondria important for cellar metabolism we inherited these mitochondrial DNA from our mother because when an egg is fertilized by the sperm, the resulting embryo inherits all of the mitochondria from the egg Components of a Gene and Gene Expression: Gene expression - when a gene is used as a template to build something (usually a protein) Promoter: where the enzyme that is going to read the DNA sequence will bind and begin to read that sequence (think of the actual switch of a light turning it on or off) Intron: need to be cut out by a different enzyme to produce a function mRNA sequence to build a sequence of amino acids and the to produce a protein Exon: Enhancer: can be next to the promotor or far of the promotor or inside the gene cell; when an enzyme binds to an enhancer it will make reading the gene (transcribing the gene) either easier or harder (think of a dimmer on a light switch either turning it brighter or darker) What is a gene? Common definition: A sequence of DNA bases that specifies the order of amino acids in a protein only 2% of the genome represents protein - coding sequences 20,000 - 22,000 genes in the human genome (this is the reality not 6.3 billion as we had mentioned Then what is all the other stuff in the genome? Non-coding DNA regions (98%): sections of the genome that are not used to build a protein example: introns Non-coding DNA can still have a function example(s): - regulate metabolism - gene expression - cellular communication Alternative definition of a gene? a DNA segment that contributes to the phenotype Two types of Genetic variation: 1. SNPs (single nucleotide polymorphisms) : single base substitution of one nucleotide for another at a particular site. 2. Structural variations: differences in individuals in big chunks of genetic code Insertions: a sequence of multiple nucleotides gets inserted into the code (into a new location) Deletions: section of multiple nucleotides are deleted or removed from the genome at a specific location Transposons (transposable elements): DNA segments that have been copied and pasted into other sections of the genome - human genome have quite a few of them - viral transposon: some of our transposon one are virus DNA and have played a role in the evolution of our immune system How is genetic variation produced? 1. Mutation Mutation rate: the likelihood that a base substitution will occur at a particular site in the germline per generation 2. Random assortment due to meiosis: refers to the gametes produced during meiosis will have a random assortment of chromosomes inherited materially and paternally Meiosis: produces 4 unique daughter cells ;these 4 unique daughter are called the gametes 3. Recombination (crossing over): when homologous pair line up at the beginning of meiosis the t wo chromosomes can over lap and exchange sections of DNA resulting in a chromosome that has a new combination of alleles another characteristic of meiosis shuffling which allele that are inherited maternally and paternally show up in the egg cells or sperm cells 4 unique cells Recombination hotspots: a location where recombination is likely to occur ; because of this some groups of alleles are more likely to be inherited together Halotype: section of alleles that are likely to be inherited together because of recombination hotspots Think of it like a finger print can be used to study patterns of inheritance and genetic diseases Linkage disequilibrium: is a measure of how the alleles that are located close together are likely to be inherited together used to study patterns to study in haplotype variation Signatures of selection: (selective sweep and polygenic selection) selective sweep : process whereby a beneficial allele increases in frequency in the population because of selection. - This will result in reduced genet diversity around the target allele Inherits as a haplotype; Allele next to the beneficial one gets inherited too Simple trait: trait that is dictated by a single trait example: t wisting your tongue Complex trait: trait that is influenced by multiple genes or the environment Polygenic selection: when selection occurs simultaneously on multiple alleles that each have a small effect on fitness - harder to detect in the genome as a geneticist Example: body size influenced by many genes natural selection can effect body size as well  September 10, 2024 Developmental Plasticity: phenotypic changes that occur in development in response to the environment that have life-long effects reaction norm: range of phenotypes that can be induced in response to variation in the environment for the given genome Epigenetics: the study of chemical modifications to DNA that are associated with changes in the way genes are expressed and how much they are expressed field focuses on how variation arises despite fundamentally similar genetics Epigenetic marks: features that are not directly governed by the genetic code that are found on a DNA molecules and regulate gene expression epigenetic marks are sensitive to environmental conditions Examples of Epigenetic Marks - DNA Methylation: when a methyl group gets attached to the DNA molecules and when this happens, it can make it easier for enzymes to read the DNA sequence and build a RNA molecules ***methyl groups are chemical modifications to the DNA molecules that either turn on (increase) or turn off (decrease gene expression)  Histone Modification - Histones: proteins that gives DNA molecular structure Histone Modification: chemical changes to the histone that makes it either easier or harder to express the gene (use the stretch of DNA to build an RNA molecule). 3D structure of chromatin - Influences what genes are expressed and how much they are expressed (depending on how unraveled chromatin is, it will determine which genes are available for genetic expression compared to others) Non-coding RNA - used to bind to other parts of the DNA molecule and make it very difficult to read that stretch of DNA and transcribe an RNA molecule and make a protein Way to turn off the gene *** Epigenetics and meiosis (sex cells are formed in meiosis): most epigenetic marks are erased during the production of the gametes once the gametes are formed they accumulate epigenetic marks (epigentic marks that are present in the egg cells, allow the cell to express egg cell genes and vice verse for sperm cells. after fertilization, most epigenetic marks are removed from the genome because now we dont have an egg cell but a fertilized egg. result -> pluripotent cells (cell that can develop into any type of cell?) ***Important in embryonic development so it can later develop specialized cells (heart, liver, etc) Epigenetics and mitosis: cellular differentiation: when a cell specializes into a particular type -> regulated by the accumulation of lineage-specific epigenetic marks (to see what type of cell will develop) methylation pattern and other epigenetic marks determine what type of cell will develop Epigenetic patterns are conserved during mitosis can be inherited if if its a somatic cell (muscle cell, skin cell, etc) except in sex cells cells are differentiating Fertilized egg The cells have different EPIGENOMES but they all have the same GENOME (the DNA code in these different cells are the same) Genomic Imprinting - Genomic imprinting: a special case of epigenetic regulation of gene expression occurs when the expression of an allele depends on its parent of origin Remember we have t wo alleles one from each parent, therefore it is important one allele to be expressed Ex: Becjwith Wiedmann Syndrome - occurs when both alleles are expressed - in a health individual, only the paternal allele of the insulin-like growth factor (IGF2) gene is expressed Symptoms include: - abnormally large tongue - abdominal abnormalities - hypoglycemia - hyperinsulinemia Evodevo - Evodevo: field of evolutionary biology that tries to understand evolution by studying development (study of evolution by looking at development) Three main principles that have emerged from Evodevo: 1. Concept of unity: refers to the fact that there is a core set of genes that are shared across animals (core set of genes that are important for development) - groups of genes that are shared across animals, work the same way across animals - ex: same photoreceptors of a fruit fly is the same photoreceptors as humans and other animals. 2. Concept of diversity: how did the same group of genes lead to phenotypic differences? - the way these genes are put together are different allowing this diversity. 3. Concept of modularity: how a packet of genes can work together to build our bodies. - group of genes that give a certain morphological output. Evodevo and the Evolution of Novelty - there are t wo types of genes that determine the body plane (how our bodies are arranged) 1. Segmentation genes: determine how the body is divided into segments refers to groups of genes that work together to determine how the body plane develops 2. Homeobox (Hox) genes: determines how organs/tissues develop within each segment coding for a protein (transcription factors) that is regulating the expression of other genes; proteins that turn on or off other genes. Ex: determines how many vertebrae’s we will have (long spine or short spine) Non-Genomic Inheritance - sometimes called Lamarckian inheritance (purposed a mechanism of Evolution that was not correct but he believed that giraffes have long necks because they are constantly stretch their necks for food, and this would somehow alter the morphology of the neck and this trait was inherited into the next generation) Non-genomic inheritance: inheritance of a phenotypic trait via a mechanism that is separate from the genetic code Types of non-genomic inheritance - - inheritance of a common environment: ex: i love to eat sweets and my son is living in an environment that we have a lot of sweets so he is inheriting a common environment and therefore, my sugar level and his sugar levels will be influenced (our biology will be influenced) - niche constriction: refers to how organisms modify their environment in a way that influences their evolutionary fitness ex: provide my son a home that is temperature regulated, so this will influences his biology as well as my biology therefore inheriting a common niche construction environment. - cultural inheritance: families culture influences our health (like yelling) so this will influence our biology and this is part of both our cultures and this will be inherited. - parent effects: can refer to biology of mother is a core component of the environment of the fetus and the environment of the infant (infant dependent on being breastfeed) - ex: body weight at birth - epigenetic inheritance Intergenerational Epigenetic Effects: Dutch and Hunger Winter - occured in 1944-1945 German blockage causes famine People has access to 30% of normal calorie intake, eating grass and tulips Sur vivors were a well documented group (good record-keeping), all of whom suffered one period of malnutrition at the same time government of the Netherlands studied how this famine affected the biology of pregnant people, offspring and grand offspring. They found that the offspring had a higher risk of type 2 diabetes, slower metabolism * egg cells develop during the and had differences in epigenetic marks fetal development compared to women that didn’t experience the famine. Is Developmental Plasticity Adaptive? Adaptation: a process of morphological, physiological, or genetic change that occurs over a range of timescales and results in enhanced evolutionary fitness at the population level. Challenging to determine in humans if a trait is an adaptation - Evolutionary fitness is not the same as health (evolutionary fitness is determined by how many offsprings an individual has not by how health or how long they life) -Humans control their reproduction therefore determining if a trait is increasing the chances that the person passes on genes to the next generation to the next. Is challenging There are t wo evolutionary explanations for developmental adaptations -> developmental adaptations: changes that are occurring during development (refers to any time before adulthood/reproduction begins) that promote survival and reproduction 1. Developmental contract model making the best of a crappy situation Improve the chances of surviving and/or reproducing today at the expense of surviving tomorrow Example: immediately adaptive response (short term) - allow for immediate survival but may have severe long term consequences developed wider hips so it can balance better on t wo legs and still get around (MAKING THE BEST OF A CRAPPY SITUATION!) 2. Predictive Models: argues that developmental cues are predicative of conditions in adulthood Individuals adjust their phenotype during development in preparation for adult environment Ex: Predictive Adaptive Response Hypothesis Also referred to as the Predictive Adaptive Responses (long term) - anticipatory responses, attempting to predict environmental conditions for mammals, the mother’s biology can be considered the fetus’s or infants environment - developing offspring receives environmental cues in the form of nutrients, hormones and other substances that cross the placenta or are found in milk offspring is inheriting signals from the mother that is going to prepare it to an environment where it can suffer famine again and the offspring is predicting an environment with constrained food  September 13, 2024 The model proposes that the adaptive response depends on the type of environmental challenge but also the timing and duration of the stress factor Homeostasis and Allostasis - Homeostasis: physiological mechanisms that defend a particular a set point (ex: temperature is 98.6 degrees; blood pressure being 120/80) - Homeostasis fails to recognize that physiological systems must respond to changing enviromental conditions in order to survive (blood pressure, temp.,etc. Allostasis: physiological mechanisms change a controlled parameter by predicting what level will be needed based on the organisms prior knowledge of the stressor and its current context System that regulates lots of stressors Ex: I know i have How is my body going to respond stage fright to my brain sending signals that you are in a stressful situation Ex: produce hormones in this case cortisol. All of our body’s mechanisms that are intune with our environment (our nerve cells, our eyes, etc); Cortisol levels Another example of Ex: having to talk in front of the class Allostasis Mechanism: shivering Acclimatization (refers to real life not lab) - stressor exposure lasts days to months (ex: due to change in season) Results in a biological response that is greater in duration, degree, or sensitivity to the environmental stimulates (ex: over time our body gets use to temp. of environment) Occurs through epigentics mechanisms, hormone dynamics or other physiological, chemical or anatomical responses. Acclimation: used when referring to a response to a single environmental stimulus in the context of an experiment (ex: group of people go into a lab, exposed to an environmental change to see how it affects the body). Beneficial Acclimation Hypothesis (BAH): Proposes that acclimation or acclimitization to a particular environment gives a performance advantage (beneficial) in that setting over other organisms Support is mixed Acclimation may not be beneficial because - exposure must be predictive of future stressor exposure - acclimation may represent wear-and-tear on the stress response system Developmental Plasticity and Development Adaptation - Developmental Plasticity: change that occurs in phenotype that occurs during development in response to the environment incomplete buffering - when developmental plasticity results in a change in the phenotype that is harmful to evolutionary fitness. Example: diethylstilbestrol - synthetic estrogen agonist - effects in pregnant women -> vaginal cancer, infertility, early menopause - effects in offspring -> menstrual irregularities, potential infertility constraint models/Immediately adaptive response (short term) Predictive models/ predict adaptive response (long term) critical window (a.k.a sensitive window/period): time period during development when the developing phenotype is sensitive to environmental conditions and the resulting phenotypic changes will have life long affects - used to understand when is the developing individual most sensitive to the environment (fetal development, infancy, childhood or adolescence)  Example: Altitude Hypoxia: there is less oxygen in your body because of the low atmospheric pressure and being in high altitude Phenotype - Environment Mismatch: mismatch bet ween developing phenotype and adult environmental conditions due to fast environmental change Example: if a person grew up at high altitude and then moved to sea level at the age of 18 (when they are mostly formed) then we have a mismatch) When do critical windows/sensitive periods exist? depends on the source of the environmental information (how the body is perceiving an environmental stressor). Critical Window/Sensitive Period: Gestation and infancy -> signals from maternal biology are most salient (significant) Fetus: coming from - environment of the fetus is regulated by the the placenta Infancy: coming from biology of the mother the breast milk - in infancy the biology of the mother is (hormones, immune factors, etc) regulated by the biology of the mother if it is recieving breastmilk childhood (and possibly adolescence) -> signals from external environment become more salient not related to the mother biology but (significant) the external environment (microbes) Epigenetic Inheritance - transmission of information across generations via the inheritance of epigenetic marks Two types: 1. Context-dependent epigenetics inheritance (fetus is affected) :developing fetus or infant receives biological signals from the parent Parental signals alter the fetus/ infant’s epigenome The epigenetic effects have lifelong phenotypic effects  2. Germline-dependent epigenetic inheritance (grandchildren are affected because the fetuses eggs were affected by grandmother; regardless of if mom was affected or not) Documented in mice and other organisms but NOT well established really in HUMANS. epigenetic patterns of the F1 GER line are directly affected by the parental signal (from F0) - causes changes in the eggs epigenetic changes persist in F2 generation despite the absence of the original parental signal Epigenetic changes occurs in the fetus’s eggs, therefore changes occur in the grandchildren as well. Phenotypic Inertia - parental signals that program offspring’s developing phenotype represents the average condition of previous generations; may decrease the chances of a phenotype - environment mismatch because signals are being passed down through generations Ex: disease risk can be passed down through generations through epigenetic inheritance  Genetic Adaptation - Genetic Adaptation: a version of the gene that improves the chances of an organism sur viving and reproducing most genetic adaptations are from natural selection acting on pre-existing alleles rather than mutation generating a new allele - few examples of selective sweep in human evolutionary history certain alleles may be adaptive because they alter one’s sensitivity to the environment (sometimes beneficial) - genetic origins of plasticity - natural selection can act on genes related to a plastic phenotype and cause it to be more prevalent, efficient or reduce disadvantageous side effects Genetic Assimilation - Genetic Assimilation (a.k.a canalization): when a particular plastic trait used to be sensitive to environmental condition but through genetic adaptation has become less sensitive to environmental conditions (evolves evolution of sensitivity) process that occurs over time (over generations) Sensitive refers to factors that are responsive to the environment Phenotype-First Evolution - when novel conditions are confronted by a population, more plastic modes are the original source of phenotypic novelty and functional adjustment Example: when a group of bears are moving into the Artic they will first rely on the adaptive modes of allostasis, acclimitzation and maybe developmental plasticity in order to survive/get by this new environment and if they are surviving well to reproduce over many generation then we can have the selection of genotypes to make that population of bears even better adaptive to the new environment. Allow population to withstand the new environment for enough time for the slower adaptive modes to evolve Why is the timescales model relevant for health interventions? in the article we had to read, it mentions that we need to consider the timing of critical period and how critical periods work and evolve to design better health interventions Author focuses in the issue of low birth weight since it is a predictor a lot of risk factors later in life (higher risk of cardiovascular disease and diabetes)  important predictor of a child’s birth weight is the mother nutrition the strongest predictor of a child’ birth weight is the mother’s birth weight (we can see intergenerational effect) High rates of low birth weight in populations where access to nutrition is limited (poverty, famine, low economy,etc) public health researchers have tried to provide food for pregnant women with the understanding that perhaps not only by feeding the pregnant women (to help her health) but also helping the health the next generation. Sensitive Period and Health Interventions: when supplementation mimics a short-term deviation from the individual’s typical experience, it is bound to have only a modest (low) influence on the offsprings health outcomes (mother experiences low nutrition throughout life-> effect of good nutrition on the fetus during pregnancy is LOW) when we continue to provide good nutrition to women for long periods of time then we start to see more beneficial effects - Instituto de Nutrición de Centro America y Panama (INCAP) - provided supplementation across multiple pregnancies - birth weight was higher after second supplement pregnancy how does this connect to our discussion? - connects to epigenetic inhertitance - trait that is influence by maternal nutrition at the time - trait that is influenced by maternal nutrition history (over life of mother)  September 17, 2024 Setting the scene (historical context of Gould and Lewontin article - Sociobiology: field that tries to explain social behavior (often human behavior) using evolution and natural selection famous book called Sociobiology as well often argued that human behaviors are adaptive to a particular environment Genetic Determinism: the idea that one’s behavior is controlled by their genes thought that violent behaviors, mental and social conditions, criminal behaviors are directly linked to certain genes Ideas popularized by Sociobiology and The Selfish Gene had major political and social implications People who agreed with this idea argued that its not worth to design social policies to prevent alcoholism, violent behaviors, etc. because the genes are there and it’s inevitable. Social Dar winism: the field of study that attempts to apply the concepts of natural selection to the field of social, economics and politics Adaptationist Program: researchers that are programmed to see everything as an adaptation “Argument that natural selection is so powerful and constraints upon it so few that direct production of adaptation through its operation becomes the primary cause of nearly all organic form, function and behavior.” idea of thinking that all traits we see in an organism are somehow adaptations for that organisms’ environment Trends they observed: - researchers argued that if one adaptive argument fails try a different one - if one adaptive argument fails asume that another one must exist - in the absence of a good adaptive arguement attribute the failure of imperfect understanding of where an organism lives, or what it does (insufficient information to understand how that trait connects to adaptation - excludes other possible explanations that doesn’t have to do with adaptation  Spandrel: the triangular area bet ween t wo adjacent arches and the ceiling they support Metaphor for traits that have arisen as by product of other adaptations Dr. Pangloss a character in the satire Candide claims things can not be other than they are, everything is made for the best purposes - we evolved legs so we can one day wear pants Gould and Lewontin’s Critique - too much focus on natural selection and adaptation and not enough focus on other explanations Just-so stories - speculative explanations for the adaptive significance of a trait in the absence of strong evidence - used to critique adaptationist program what kind of evidence do we need to support an adaptive hypothesis? - Need to have comparative research (we have a group of organisms that do have that trait living in the environment and a group that dont, are the organisms surviving and reproducing How can we test the null (alternative) hypothesis? Argue for a pluralistic approach - Evolutionary biologist need to look at multiple lines of evidence, cultívale population of the organism, multiple experimental designs in order to say something is an adaptation - Evolutionary biologists should also consider constraint and allometry Constraint: features in an organism’s form or function that restrict what types of phenotypes can evolve - phylogenetic constraint: when a particular feature is present in an organism due to its evolutionary ancestry - developmental constraint: in complex organisms early stages of development are resistant to evolutionary change because the development of organ systems and their integration into a functioning body is such a delicate process if there is a small change in a structure of the heart during fetal development, as the organism grows it can cause failure of the whole functional body  Allometry: the change in size of one biological measure with respect to another (often body size) example of contraint something might be a particular way just because it is constrained by other features of the body Gould and Lewontin’s Critique - Genetic drift, neutral mutation and gene flow produces most variation a trait must be considered in the context of the complete evolutionary history of the organism that carries it rather than just the present context in order to determine if it is an adaptation or not “Sur vival of the fittest” versus “survival of the barely tolerable” Some traits may be adaptive but may be described as “survival of the barely tolerable” Discoveries of the Human Genome Project - 1. Humans have fewer genes than we thought 2. Most of our DNA consists of non-coding sequences - regulate the expression of other genes 3. Most of our traits are complex traits - influenced by multiple genes and the environment Motto Kimora and Neutral Theroy - argues that much of the variation at the molecular level (sequences of genes) is not generated by natural selection Genetic drift and neutral mutation produces most genetic variation  Neutral mutations are common because - large nonfunctional selections of DNA code - redundancy in the code (meaning the sequence for a particular gene can show up in multiple parts of the genome; if in one place there is a mutation its okay because there is another functional part in the genome) - a change in amino acid may not affect the protein Neutral mutations can, in absence of selection, explain why a feature may disappear over generations eyes have gone away through evolution but not natural selection Fish that didn’t have eyes can still reproduce as efficiently as those who had eyes (eyes didn’t stop reproduction) Genetic drift and allelic fixation - genetic drift can have a really big effect in variation of a trait if the population is small Example: a group of people that are migrating to a new environment and they have a particular eye color. The eye color isn’t adaptive to the new environment or it isn’t that the eye color is more sexy, it just happens to be that the small population that moved to a new environment has a high frequency of the eye color, and their descents as well just by chance (genetic drift) Rebranding of Sociobiology as Evolutionary Psychology - greater recognition of the role of development Still uses adaptive explainations Side Note (Recall): Examples of Spandrels - Evolutionary spandrel: a trait that has arisen as a byproduct of other adaptions sometimes co-opted for a new use, but evolved due to the evolution of a different trait Examples: bellybutton Hump of Irish deer The Orchid and the Dandelion Hypothesis (evolved in the field of evolutionary psychology - The evolutionary hypothesis argue the following… “Both stressful and supportive environments have been part of the human experience throughout our evolutionary history” “Developmental systems shaped by natural selection respond adaptively to both kinds of contexts” “When people encounter stressful environments, this doe snot disturb their development as direct or regulate it toward strategies that are adaptive under stressful conditions” These researchers are observing that there is a relationship bet ween exposure to extreme psychosocial stress during childhood and stress reactivity in adults Example: children that experienced more instances of abuse -> are more likely to grow up to adults with a stress regulatory system that is very sensitive and can trigger the stress response very easily (this pattern is often correlated risk of anxiety disorder, depression,etc. WHEREAS, individuals that grew up in more supportive environments tend to have less reactive stress disorders. Orchid: children that are sensitive to the environment (poor/stressful environment -> high anxiety and stress in adulthood BUT a nurturing environment -> very beneficial outcome in adulthood Dandelion: children that are less sensitive to environmental conditions (ex: can be in a stressful environment or non-stressful environment and regardless will thrive what are your initial thoughts regarding this hypothesis? How does the hypothesis fit the current environmental context? the hypothesis is built on the assumption that humans exhibit a bimodal pattern (distribution of a particular trait that have t wo phenotypes that are common in the population What types of evidence would need to collect to test this hypothesis? evidence does not show bimodal pattern, most people are in the middle (spectrum) how may high or low environmental sensitivity have been adaptive in our evolutionary past? How can we collect evidence to test the adaptive significance of differential sensitivity? What are the possible alternative hypothesis?  September 20, 2024 PBS Movie: The Eugenics Crusade 1. What was the main argument of the eugenics movement? Claimed that they were trying to improve society by planned reproduction (planned breading) This idea that most of our traits are dependent on genetics, therefore some individuals with more benefícialas characteristics should be able to reproduce and individuals with “not beneficial” characteristics should NOT reproduce People who were out of the white wealth and white middle class population, were viewed as not fit for reproducing Because of this movement there is a significant history of forced sterilization in the US (specifically blacks, indigenous, people who had some sort of mental issue, low income people 2. Why did the eugenicists think that the eugenics movement would improve society? people believed if the individuals who had the “not beneficial” characteristic were prevented from reproduction (having them have forced sterilization), then there would be a way to create the perfect society by choosing those who were “best fit” to reproduce.