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ALL Evolutionary Psych Lecture Notes - Beginning To End

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York University
PSYC 3420
Irwin Silverman

Sep 16, 13 - Overview of Darwinian Theory. Evolutionary psychology compared to traditional psychological approaches •The planet earth appeared about 4.5 billion years •First signs of animal life on the planet occurred about a billion years after that • The first forms of life were really simple e.g. bacteria •Nothing more complex than algae was alive •Then there was an explosion of life forms- Cambrian explosion o Cambrian explosion was the relatively rapid appearance, around 542 million years ago, of most major animal phyla o Sponges, jelly fish, worms •Darwin’s theory explains how and why this kind of evolution occurred •Has nothing to do with how life originated • Began with a huge lightning storm, if you combine the elements that we assumed were in earth you get amino acids, they think life started like this •Darwin collected minerals, read a lot, collected birds and insects •He went to medical school, his father pressured him • He went on a 5 year trip, he didn’t have a reputation as a naturalist •He would go so his friend (the captain) would not be bored •Their relationship didn’t work, they fought about religion •Religion views at that time didn’t exclude evolution • Do species come from other species? Or did God create life? •Fitz Roy was a fundamentalist- things God created life •Ship got off at the islands and the things he saw their drove him more to realize evolution exists • Darwin published “evolution by natural selection” 25 years after the voyage •Fitz Roid disrupted his meetings and finally he killed himself (went insane) •He took his notes back with him and studied them for a few years before he came up with the idea of natural selection • The thing that gave him closure to the theory was an essay by Thomas Melfas, “human populations would double every 25 years if there were enough food supply.” o Organisms tend to be different from each other in some way and at least some of these differences are based on heredity o Organisms tend to overproduce than their own replacements •Adaptive: better able to cope with environmental survival, survive to the point where you can have offspring o Individuals that are adaptive tend to live longer and reproduce and will inherit traits that are more adaptive (selected for) •Birds were different in beak structure, even though they lived on the same island, differences evolved by natural selection •Birds in the desert had long slender beaks these allowed them to sip nectar from cactus plants •Birds in the _________ had short strong beaks • Two types of shells: perfectly oval domed shape and the other was a saddle-back o What he theorized is that turtles that lived on the ground had the domed shape shell o Turtles above the ground line developed the saddle-back shell • Fitness in a Darwinian context, did not refer to bravery or intelligence, only to traits that best suited to the animals environment (the animals ecological circumstance) o Not socially positive traits Why do we tend to worry more than we need to? o Those in the primitive environment that worry less than needed have less ???? • Normally people don’t deliberately worry more than they should • Example: the ancestors of the giraffe had longer and longer necks to access food • Example: the ancestors of the human had evolved a thumb • Example: behavior in animal for food searching • The theory applies to much more complex behaviours in both animals and humans o In humans it applies to consciousness, intelligence, etc • Evolutionary subconscious is saying that everything evolves in the way that any organ evolves - natural selection Sociopolitical aspect of the Darwinian theory: • The phrase "survival of the fittest" - by spencer o An alternative description of natural selection • Competition is the natural order of things, this is what we do • We want to out survive and out reproduce • Spencer's two notions: o Naturalistic fallacy: the mistaken belief that what is a natural is also what is good (what is and what is out to be) • The concept of what's out to be comes from the heart o What is natural is unchangeable • This theory Led to the concept of social Darwinism • Implies a social Darwinism, if you accept this theory than you accept the way of social Darwinism as a way of life • Marx was a fan of Darwin's theory • He believed Darwin's theory evolution by natural selection contains the basis of natural history • He tried to reach Darwin, but Darwin wouldn’t respond to him Why evolutionary psychology? Why Darwin? • All sciences share the same goal, and that is to understand the causes of things • We can calculate cause in terms of: o approximate causes o remote causes o immediate causes • Ex. If we ask where does rain come from? You give an approximate cause (comes from the clouds) • Ex. In psychology, why are some people overweight? What is an approximate answer? That they eat too much o But it raises another ultimate question, so why do they eat too much? o So each ultimate answer leads to another question • Ex. Most everyone likes sweets, but why? Give me an approximate answer o Sugary stuff activates the pleasure sensation from the tongue to the brain • The problem is that this is as ultimate as the psychology textbooks become • Individuals who prefer the taste of sweet ate the right food and took in the right sugars for survival, and those who had different meal got very sick (basically didn’t survive very well) o This is a very ultimate explanation that seems useful o So why don’t psychology texts teach you this? Because they tend to be extremely approximate with their approach o Ontogenetic Development - development from the day you are born to the day that you die • Psychology focuses on ontogenetic development o Phylogenetic Development - Your evolutionary history, everything that happened before your conception • The basic question for scientists who study families, in the animal, why • Why do we have language in the first place? • How and why did our communication system developed? • The big finding was that they were able to put two concepts together o “purpose of communication” o What would traditional psychologists say about all of this? • One point of view • Different approaches • Each has its own value • In evolutionary psychology we don’t make a dichotomy between the proximate and combined approach • We need to look at both in relation to each other to get the whole picture • Study HOW it works and WHY it works • If a small child asks you what makes it rain and you told them the clouds • Why does sex exist at all? Instead of splitting in half, giving off spores • The most common problem of couples is the decrease in sexuality as the relationship passes the first year or so o Therapists try to bring it back to past levels o Let’s female focus time on the offspring o Males drop in testosterone level after a child is born • How did we get brains o For the evolutionary theorist= because we have a brain, we can do these things o Evolutionary psychologists= because we did these things, we got the big brain • We didn’t become tool makers because we have opposable thumbs, we have opposable thumbs because we were tool makers • Saying that something is based on culture is not a scientific calculation e.g. someone born in a certain ethnic group • WE CAN’T SEPARATE CULTURE FROM BIOLOGY • If you believe in accidents, you’re not a scientist anymore • All events are caused, you just have to find the cause • No other science except psychology ignores its ultimate question • For Maslow, we have a hierarchy of needs and thus are not motivated exclusively by physical requirements (food, water), but as well motivated such as self-actualization, the need to fulfill or realize our full potential • Advanced psychosocial needs at the higher level • “Man does not live by bread alone”, an ancient, biblical source • Motivated to satisfy OTHER desires such as affiliation- that can be reduced to attachment Sep 23, 13 - Mechanisms of natural selection: Sources of genetic variation; directional vs. stabilizing selection; punctuated equilibrium • Darwin waited 20 years to present his theory, and even then he presented it out of pressure • He would collect specimens and would sell it to biologists • Theory: oriented more towards group selection than individual selection • Darwin presented his theory jointly at a biology meeting • Why did Darwin wait? He was not really sure • How do we get from bacteria to humans? It seemed like too much of a task that would be done by natural selection • Depends on the association of some environmental change TWO IDEAS 1. Earth was 6 million years old rather than 4.5 million years old 2. The theory of inheritance/blending: offspring’s are born with attributes of the parents • Gregor Mendel was a priest and he made discoveries that would resolve blending (blending of the protoplasm) • He would try to get different types of peas, what he noticed it would always come out in ratios of 3:1 therefore he found out the theory of dominant and recessive traits • Gene is the unit of heredity • The units of heredity (genes) are passed on as articulate, any evolutionary advantage an animal has will be enact, it will not be blended back • Mendel was aware of Darwin and tried to communicate his findings to him • Natural selection was then talked about as genes instead of traits • Synthetic Theory of Evolution-it synthesized Darwin’s and Mendel’s theory o a.k.a “Modern Synthesis” o It explains evolution by merging Mendelian genetics with Darwinian Theory, and shows how natural selection leads to evolution • The significance of this synthesis is that survival is no longer limited to individual survival, it is the survival of the individual’s genotype, NOT the phenotype • It explains parenting behaviour • Our genes not only enable us to survive but to be good parents because of the genes to be good parents will outweigh the ones not to be • Advantageous genes include parenting behaviour • Natural selection requires variation/genetic differences WHAT ARE THE SOURCES OF VARIATION? • The most commonly known and stated method is mutation o It’s is the primary mechanism of evolutionary change o Most mutations are deleterious (causing harm/damage) • Process of sexual reproduction o When the female and male gametes unite, it forms a new combination o This can contribute to variability in the gene pool o E.g. you and your sibling will have a different combination o This is the rationale for why sex evolved, contribute to variation, contributes to natural selection o It still seemed limited o Discovered in the 1930s how sexual reproduction can contribute to variation: Recombination o GENE SHUFFLING, CROSS OVER PHENOMENON- happens in meiosis  The process where the pairs of chromosomes split to form the gamete (sex cell) o Cross over phenomenon: quite prior to the split, they exchange material o Every cell in your body is different than every other gamete, none are the same o Cross over has replaced mutation DIRECTIONAL SELECTION • Is a mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype • Under directional selection, the advantageous allele increases as a consequence of differences in survival and reproduction among different phenotypes • The increases are independent of the dominance of the allele, and even if the allele is recessive, it will eventually become fixed • The kind where evolutionary change species become subspecies • Drives change • Change in environmental conditions causing one phenotype to replace another in the gene pool, change does not occur on individual basis (only on the entire species) STABALIZING SELECTION • Is a type of natural selection in which genetic diversity decreases and the population mean stabilizes on a particular trait value • This is thought to be the most common mechanism of action for natural selection because most traits do not appear to change drastically over time. • Stabilizing selection commonly uses negative selection (a.k.a. purifying selection) to select against extreme values of the character. • Stabilizing selection is the opposite of disruptive selection • Leadings to greater specialization • Species come to occupy an ecological niece • Will reach the point of maximum adaptation DISRUPTIVE SELECTION • Describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population is divided into two distinct groups • Wolves, dogs • Dominance • They survive winning encounters Why doesn’t all selection ultimately become stabilized selection? • RED QUEEN THEORY - Is an evolutionary hypothesis which proposes that organisms must constantly adapt, evolve, and proliferate not merely to gain reproductive advantage, but also simply to survive while pitted against ever-evolving opposing organisms in an ever-changing environment • The Red Queen hypothesis intends to explain two different phenomena: o The constant extinction rates as observed in the paleontological record caused by co-evolution between competing species o The advantage of sexual reproduction at the level of individuals • Alice asked the red queen why am I running all the time • Sometimes you have to keep running to stay in the same place • That tells us one explanation of why we have so much variation • For example lions and antelopes • Lions live as predators mainly on antelopes • As the lions hunt a population, the slowest ones will be caught easily • Fastest and smartest will survive • The lions also have to be the fastest to survive, so it’s race • The prey species will develop adaptations in order to survive and predators will develop adaptations in order to catch the prey • Humans show the most amount of change • Viruses are our predators • It is viruses which can contribute to evolutionary change (genotypic change) • If it were not for our intelligence and knowledge, we could not control the aids epidemic • Eventually there would have been physical and psychological changes • Our predators are other people! And most of human directional selection is assumed by biologists to be based on internal competition rather than competition with OTHER species • The data showed this! Shows consistent evidence of individual conflict • People who can find better ways out survive other people (better ways) • The social anthropological theory is that the brain development did evolve by natural selection because of cooperation (they were able to do more things and develop more things) rather than developing their brain through competition • Competition is in our genes • Kurt Myer - Natural selection which leads to change within species and eventually within new species happens when a small percentage of the population is isolated o The separated subpopulation • Darwin suggested that evolutionary change was gradual • The current version of Kurt Myer o Performed by Mill Eldridge - he in ruled that the most significant evolutionary changes are episodic (they take place within a 100 or even 1000s of years) and take place in large place of environment • Permanent extinction - 100 million years ago - in this extinction about 50% of species became extinct o The fusion of the land masses underneath our seas created shallows of waters which decreased the food source from water, resulting in the extinction of land animals • Ice age – a.k.a crustaceous extinction - 75 million years ago - 1/4 of species on earth were eliminated, most were large reptiles o Gave rise to the mammals shortly after •These are what resulted in the intense variation of species and also natural selection in the first place - with the rapid environmental changes •This also explains why in the fossil records that there is no direct record of species disappearance •The fact is that the species (based on the Rule and Elders theory) evolved faster and more quickly because of the rapid changes in the environment - and with the extinction of older species it resulted in the start of new species •Australopithecus Africanus - the earliest identified of homo sapiens o Fossils of 3 million years ago are virtually the same as the ones as 1 billion years ago (when they were extinct) o Speciation happens to quickly to be directed into fossils • Territorial acquisition, and etc, we could find in the earliest finds of the homo sapiens • If we extrapolate this to evolutionary psychology, you can understand why people on different ends share similar traits - we are more alike than we think - we have the same priorities • The evolutionists focus on the sameness of the humans; equilibrium 1945, Bernuck -made a point about punctuating equilibrium • He was a psychologist - he made a list of traits known to exist in every culture in history • Age grading, athletic, community, cooking, corporative labor, decorative art, division of labor, education, ethics, etiquette, funerals, games, gestures, gift giving, hospitality, language, law, housing, hygiene, etc. Sep 30, 13 - Levels of selection: Individual, group, kin, gene. Levels of Selection: • Theory of science was a conceptual tool • In science the primary use of theory is to get to something Darwinian Theory: • Was not able to explain altruism o Has two definitions: social and biological o Any behaviour that enhances the other o Altruism does not deal with motivation • One of the benefits of Altruism: Reproductive reinstrength • The relationship between the amount of food a population can consumes increases and then it reaches a peak, called the critical maximum where you can no longer consume any more • Ex. Animal food: in which you hunt, feed off the weaker animal by hunting, it results in the stronger animal to exist and the weaker animal to disappear • Ex. Plant food: harvesting a crop, until you can no longer harvest any more • Observation from his species seem to have evolved behavioural strategies to control their own reproduction • Different ways that this mechanism (controlling their reproduction) operates: o One way called optimization - By Lack, how females control the rate of the reproduction the female has the capacity to control how soon or how often, or how many she makes eggs. If the population is overcrowded the eggs will decrease, if population is under crowded number of eggs is increased (BIRDS) o The way the female specie takes senses o One naturalistic study in optimization in birds: the intent to control the crow population in a Scottish village o They would pay you for every dead crow o And this intensive worked and they saw results o In a psychologists work: Kahoon on the effects of overcrowding in rats - building a colony of rats and then overcrowding the colony - the female rats became infertile, males became homosexual and they optimized o Our data would suggest you get optimization in life form as viruses o They found that the viral rates declined, virus as some intrinsic mechanism controlled the rabbit population o Sneezing is a form of population control (a form of virus) o The physiological response of humans (ancestral history):  When a female doesn’t get enough food, ovulation shuts down  Teens become more sexually active and more pregnancies in populations where food shelter etc are highly available o Helpers adonecent?: some birds stay to help the mother with the younger siblings (seen in mammals and birds) o Animal sacrificing themselves in the face of threat to protect the crew o Thompson Guisele (from textbook) o Seen in bees, alpha baboons, and young homo sapiens Selection happening at the level of population 1. INDIVIDUAL SELECTION: refers to competition with another one individual (ex. Classmates) 2. GROUP SELECTION: refers to competition between a group for within the group(ex. Basketball) - the team that gets to work together cooperatively gets to beat the other team o Misconceptions: a. Group section implies survival of species • It's too wide of a scope - nobody dies from their own kind of species b. Groups selection does not include individual selection c. In humans: group selection are to outsurvive those who are not within a group 3. KIN SELECTION: o kin selection (textbook doesn’t talk about KIN selection, inclusive fitness MEANS the same thing which is talked about in the textbook) o More altruistic to relatives that share more of your genes o Twice as nice to siblings than nieces and nephews (altruistic) o Hymeaopteran- includes some species of ants/bees o Eurosocial- denoting social organisms (e.g. the honeybee) in which a single female or caste produces the offspring and non-reproductive individuals cooperate in caring for the young o We are programed to help generations o Many Hymeaopteran were haploid/diploid o Haploid-diploid species- males come from non-fertalized eggs, so they have one set of chromosomes instead of a pair  They are more strongly related to each other than they would be to their own offspring  They share 100% of their genes (with their father) 50% mother 75% sister  They become sterile so the queens could generate more sisters to have  You don’t need group selection to describe things like this o Diploid-diploid species: have one set of chromosomes for males  Daughters of males possess 100% identical of their father 4. MULTILEVEL SELECTION: All three levels is operative in the individual o Getting the best for yourself o Ready to sacrifice resources to the group o How far does kin selection extend? o Some say up to 2 cousin o Others say ethnic wars are for pragmatic reasons-land reason and power o Dumb nephew theory:? natural selection would have favoured the ability to form the most effect and changeable alliances, if you’re committed to your kin, you are limited o E.g. your brother says give my kid a job, and you are obliged to o Ethnicity is often the rationalization for the war [Wars are labeled ethnic- they tend to be involve genetically similar groups] o Civil war-1990- As the economies went down and conflicts began, ethnocentrism increases, but always the economic conflict preceded 5. GENE SELECTION: All natural selection operates at the level of the gene o Productive theory- one that can generate hypotheses o The only way we can observe the operation of the genotype is through the phenotype o Morning sickness is an adaptive function, infant pushing the mother into information that she was feeding him toxic food Oct 21, 13 - Genetic variance in human individual differences: Behaviour genetics TEST: 60 from text 20 from lecture Human Genetic Variability • Science of behaviour genetics the degree at which the environment creates differences between individual species •This field began with animal search •Because you can experimentally manipulate heritability and environment of animals •Two varieties of animal studies: o Selecting breeding experiments : manipulate heredity while keeping environment constant • Ex. With rats - continuously breed mice high in a trait with another mice high in that trait and a mice low in a trait with another mice low in a trait - measuring high and low traits • Breeding for different types • Raise the animals that have bred over several generations that have been high in aggression and animals that have been bred below aggression • You get to see how much they differ • The difference is a reflection of heredity • How much a trait is due to heredity • Ex. Mouse A is aggressive raised in this environment etc. o Inbreeding experiment: manipulate environment while heredity stays constant • Back cross animals • Breed pairs with offspring and offspring back with each other • Raised in diff environment • Any differences you get is a function of environment • Because the rats will eventually be identical twins • Divide half mice (half trained to run mazes other not trained) •These experiments can be done with people o Non experimental approaches you can take o Natural occurring events that can take to make changes o 1st condition: heredity varies, environment constant • Identical twins (identical in genotype) raised in the same household • A strong relationship you find between them • The actual correlation with twins raised in the same household in height is 0.9 • This is evidence of heredity or environment or combination of these • But suppose you compare identical twins raised in the same household and fraternal twins raised in the same household • In both cases, members of the pair have the same environment, but in terms of genetics the fraternal twins share 50% of genes, while identical twins share 100% of their genes • If you find a significant diff - then you have evidence that heredity plays a role in the change • Height for fraternal 4.6 and height for twins 4.0 o 2nd condition: sibling rear apart from birth • Identical twins raised apart from birth in diff environments • Their environments aren't too similar • Any significant difference between their traits - then its evidence of heredity • No effect of environment correlation would be 1 • No effect of share environment defined as being raised in the same household •Whether heredity or environment plays some role is used in research by behavioural genetics •We can tell whether if something is based on heredity or not and also the reason why •The fraction that defines the role of heredity called heritability - defined statistically as the proportion of phenotypic variation is due to genotypic variations o How much of a diff between individual is based on heredity o How do we measure this? o Simplest index of heritability is the correlation of twins reared apart assuming the environments are uncorrelated then all the relationship of all the traits between would have to be a change due to heritability (in this case height is 90% due to heritability) o Assumption if there were any correlation between RANDOM matched pairs in class for example, is due to heritability (genetics) •One measure: o Based on correlation of twins reared together between correlation of twins reared apart o In this case heritability can be calculated by heritability by diff of correlation reared together divided by difference of correlation between twins reared apart and double this number o Correlation of identical twins is composed on influences of genetics and environment o Correlation of fraternal twins is composed on half the genetic influences and all the influences from environment o Algebraically: diff between identical and fraternal = 1/2 of heritability o What's heritability of height based on this method? o 90 for identical and 45 for fraternal roared together o Why are they the same figure as those twins reared apart? SOMETHING about the adoption agencies…. o Ex. Uncorrelated environment HAS an effect = heritability of IQ Heritability of IQ • Adaption agencies will tend to match on the base of education level, occupation, and so on • The correlation for identical twins reared apart .72 • For identical twins reared together the correlation is .86 • Fraternal twins reared together .60 • More advanced measures so they say that the additive genetic variance and non- additive variance • Additive variance: means that it is compatible in an additive way (linear relationship) • Non-additive Variance: means there is an interaction The data • The most widest study has been IQ • Because it is convenient, it is available, it has a wide range of material • As people get older, heritability of IQ increases-the older the group you study the more heritability they will show • Your resemblance to your adopted family in IQ decreases and your biological family whom you’ve never seen increases • Parents are less involves in their kids as they get older (the foster parents) • Different capacities of learning developments occur at different stages • Adoptees claim as they get older they have more of a yearning to find their parents • Not because they were not prepare but they felt things emerging in them • Yushar- laboratory in the Midwest he would bring together twins that are reared apart • One of Oprah’s programs decades ago • Twins raised apart recently reunited and they were chatting about their lives • He helped two people in located their parents, and both of them insisted that he was there when they meet Specific cognitive abilities • Memory • Conceptual speed • Heritability estimates around 40% • Study shows that reading abilities showed up at .30 Personality • Focused on 3 traits • British psychologists: Isang • Theory of personality: boiled down to three components • Emotionality the tendency to be aroused to negative emotions such as fear • Extraversion • Activity levels • Heritability estimates .30 or higher • The largest lab is the Minnesota Quin project • To get estimates between .50 and .75 for a variety of personality estimates which include sense of well-being HIGHEST ESTIMATE THEY GOT • This turns out to be the most heritable trait • The data of the studies that have been published recently: people that win lottery tickets and after a year if the person was happy and optimistic or depressed or complaining and paranoid • A year later they have the same attitude .82 heritability rating Some attitudes of Lisa’s study • Conservatism: it is between .30 and .50 • Doesn’t mean there is a gene for conservatism • He can never find a study for the heritability of liberalism • You get a larger array of motives that draws to liberalism • Schizophrenia, bipolar disorder- estimates vary greatly: shows that this illness is physiological based • Certain heritable personality traits such as shyness and aggression do have high heritability rates • Once you go to a mental health professional, it is not hard to get a diagnosis of some kind • There is much evidence of the heritability for criminal behaviour- heritability of psychological traits that can bring you in the conflict involved • Testosterone level tend to make you more aggressive • High testosterone and you are raised in a lower socioeconomic status environment, you are more likely to be a criminal • High testosterone-upper classes- more likely to be a criminal lawyer • Most studies show NO effect of environment for shared environment • The correlation for unrelated people reared together tend to be 0 • Which means that environmental similarities do not account for personality similarities • What kinds of non-shared environmental effects? Everything that parents do e.g. living together and you are being treated differently • Some studies show HIGHER correlations on some personality on identical twins reared apart than together • Reared together, they are trying to be different – sense of individuality • The non-shared environment-kids outside of the home TUTORIAL • Nancy Segal, book: born together reared apart • Scientists still don’t understand why a single fertilized egg splits in the womb • Twins have a lot to reveal about us • Twins reunited after 35 years apart • Separated twins are very alike- genes are a major part • One was raised with her biological mother one was raised with her alcoholic stepfather • Her bond was instant • More familiar than a best friend Nov 4, 2013 Ecology: the study of the relationship between animals and their environment Behaviorual ecology: animal behaviors and their environment Socioecology: relationship of an animal’s social behaviour and their environment Ecological niche: aspects of an animal’s environment that are critical to than animal’s survival  mating opportunities, food source, etc. • Look at socially close species and their behavioural patterns, and then differences in the aspects of the environment that pertain to survival. Then they look at ecological niche. Socioecology  Largest study was Weaver Birds they are a type of finches. They are composed of 90 subspecies. Great diverse behaviour patterns within these subspecies - Crook: did the bulk of studies in socioecology. Studied mating strategies and other social behaviour. Group behaviour of Weaver birds: tend to be solitary. Spend life alone or with mate, and others travel in large flocks (gregarious flock). Solitary vs. gregarious Mating patterns: some species are monogamous (stay with the same mate for a whole season), and some stay with them longer. Some are polygamous (one male, multiple females). Parenting: some Weaver birds share parental responsibilities (guarding the nest, feeding the babies), and in others, solely the female remains behind to take care of the babies. Monogamous ones are the ones that shared parental responsibilities. Sex differences: sexual dimorphism  differences between sexes in the species other than in terms of reproductive apparatus. Differences in size, plumage etc. Males are more aggressive than females. The critical ecological variables underlying these differences were 2: • Food source: what the animal eats • Predation: what wants to eat the animal Analyzed how these ecological differences determined behaviour. - The most direct effect is on group behaviour. Where the animal lived (solitary or flocks) - Effect depends mainly on whether the food source is dispersed or patchy Species in the forest lived mainly on insects  they are a dispersed food source (scattered evenly around the terrain). It is more adaptive for the animal to forage ALONE. Weaver birds in the forest divide the habitat into territories that are occupied by a single bird or pair. - Birds who lived this way were fitter than birds who did not. Birds who traveled in groups would not survive in the food source that is dispersed  find a food source, and can only feed one or 2 birds. Weaver birds in open plains (savanna) feed on grain, and grain is a patchy food source  spread wider, and is in abundant quantities when it is found. Increased likelihood of finding food if the group searches together than solitary. Predation
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