Evolution - Week 6

Week 6 - Social Development, Kin Selection and Families Unit 6.1 - Social Development ● What is development for? o Extended period of sexual immaturity o Unable to reproduce o Must develop from a single cell organism into a functioning adult ● Life History Theory o Principle of allocation ● Time and resources are not infinite ● Invest differentially in growth, survival and reproduction at different life history stages ▪ You could take longer to develop so you grow bigger ▪ Run the risk of dying before reproducing ▪ Timing of reproductive years is chosen by selection o Differential allocation depending on current environmental context o Somatic effort ● Growth, development, learning ● Survival o Reproductive effort ● Production and rearing of offspring o Trade-offs in life history stages ● Developmental trade-offs ▪ Many trade-offs need to be made in terms of parental effort ▪ Few or many offspring? ● More offspring you have, less parental investment you can give to each one ▪ Eg, fish lay hundreds of eggs, but only a few survive ▪ Contrast to us where we have few offspring, but lots of parental investment ▪ Incur costs when resources are scarce? ● Eg. If starving, do you feed baby with risk of dying yourself? Or do you let baby starve because you can have more babies in the future ▪ Mature quickly = invest less in growth, learning ▪ Invest in learning and growth = delay in reproduction ● Variation observed within and among species ● Stable environment leads to longer term investment ▪ If environment is predictable, makes sense to develop long term, and reproduce later in life ▪ Social stability and development ▪ Father-absent homes ● Boys: ▪ More aggressive ▪ More rebellious ▪ More sexually exploitive views of women ● Girls: ▪ Earlier puberty ▪ Shorter term relationships ● Life history view: ▪ Father absence potential cut to ● Social instability ● Female biased sex ratio ▪ Shift trade-off to ● Advance age of reproduction (less somatic effort, higher reproductive effort ● Favour shorter-term mating strategies ● Play o Non-purposeful behaviour, usually in juvenile animals o Usually incomplete behaviours (not goal-directed) o Various types ● Social play (social interaction ● Locomotor play (exercise) ● Object play (manipulate objects) o Benefits ● Learn acquired skills (cognitive, social, and physical) ▪ Hunting techniques ▪ Social skills such as grooming ● Facilitate neuromuscular development ▪ Connectivity in cerebellum, neuromuscular synapses o Life history view of play ● Somatic effort - invests in growth and development as opposed to reaching sexual maturity ● Should occur in stable environment with higher probability of future reproduction ▪ Lambs play less when food deprived ● However, kittens from food-restricted mothers are weaned earlier and played more ● Counter to life history theory? ▪ No, if you look at the TYPES of play behaviour, still consistent with theory ● Kittens increased object play ● Reduced social play ● Potential to maximize current survival at cost to future social success/reproduction ● Attachment Theory o Social development in our own species o John Bowlby ● Infants/children form a 'working model' ▪ Mental representation of cognitive and social environment ▪ Formed early in life, 6mo-3 years ▪ Used to guide future behaviour o Mary Ainsworth ● Developed strange situation test to measure attachment type ▪ Bring caregiver in with baby ▪ Mother sits in chair, baby starts playing, mother leaves, kid reacts, and mother comes back ● How does child respond to mother's (or caregiver’s) disappearance/reappearance ▪ Secure ● Cries when mother disappears, seeks attention when she reappears, resumes playing after being comforted ● Have long-lasting stable relationships ● Approximately 2/3 of children ▪ Insecure avoidant ● Show little attention to mother, little distress when she disappears ● Short relationships than securely attached people ● Approximately 1/4 of children ▪ Insecure resistant ● Remain very close to mother, distressed when she leaves, not easily comforted after she returns ● Over commit to few relationships (super clingy type) ● Approximately 1/10 of children o Attachment styles ● Often thought of as a continuum with secure in the middle ● Proportions of types variable from culture to culture o Attachment and life history ● Insecure attachment predictive of: ▪ Mental illness ▪ Delinquent behaviour ▪ Is insecure attachment behaviour maladaptive? ▪ Or adaptive response to unstable environment? ● Darwinian medicine approach ▪ Apparently negative responses may be positive adaptations to negative environmental variables ● Eg. Fever - response to infection; what we often think of as sickness, is actually an adaptive response to infection ● Can take this view on development ▪ Early attachment may serve as cue as to degree of social stability o Attachment styles as adaptations ● Two authors have proposed life history theories of attachment ● Belsky (1997) ▪ Secure: ● Parents investing more heavily in fewer offspring ● Child responds to stable, nurturing environment ● Longer-term mating strategies ● Adult Attachment Interview ● Higher levels of relationship security ● Longer relationships ▪ Insecure-avoidant ● Parents engaging in short-term mating strategy ● Less investment into each offspring ● Child responds to socially unstable environment ● Shorter term mating strategy response ● Accelerate sexual maturation ▪ Insecure-resistant ● Parents engaging in short-term mating strategy ● Less investment in each offspring ● Child response to null reproduction ● Forego reproduction to assist family ("helpers-at-the-nest") and siblings in reproduction ● Children more likely to be 'mothering' in relationships ● Developed instead of short term relationships like in insecure-avoidant ● Style most common in first born daughters ● Chisholm (1996) ▪ Similar life history theory approach ● Distinguishes between parents unable and unwilling to support children ▪ See table 6.3 in text* ▪ Secure Parental strategy Child's strategy ● Long-term mating ● Maximize long-term ● Able and willing to invest development and learning ● High parenting effort ● Maintain investment from ● Unconditionally accepting, parents supportive of child ▪ Insecure-avoidant Parental strategy Child's strategy ● Short-term mating ● Maximize short-term ● Unwilling to invest survival ● High mating effort ● Avoid potentially ● Dismissing, rejecting of neglecting or infanticidal child parent ▪ Insecure-resistant Parental strategy Child's strategy ● Short-term mating ● Maximize short-term ● Unable to invest maturation ● Parenting effort with ● Maintain investment from insufficient resources parent ● Inconsistent support, not rejecting o Life history and attachment ● Proposes that apparently dysfunctional response is adaptive developmental response ▪ Or was adaptive in EEA ● However, ▪ Studies of hunter-gatherers fail to support this ▪ Father absence effect on age of reproduction not found ● Shows that this is not a universally adaptive response (may be other explanations) ● Also, this account may overestimate importance of parenting ▪ Shared environment accounts for less variation than shared genes ▪ 'attachments styles' may reflect inherited personality traits, not effect of parenting ● Failure to account for sex differences in personality and reproductive behaviour ▪ Lot of developmental theorists are being environmental determinists ● Behaviour of parent does not determine behaviour of offspring ▪ A lot of traits could be inherited and genetic and won’t depend on environment/learning ● Belsky and Chisholm models make few predictions about sex differences ● Males and females have different optimal mating strategies, may differ in response to attachment ● Sex differences o How do they develop? ● Consistent differences in personality traits and reproductive traits between sexes ● Standard assumption was that these differences were result of parenting style - WRONG o Last decade, increasing acknowledgement that sex differences are important o Although much overlap between, sex differences in a variety of psychological measures o Comparable to sex differences in height/weight ● Distribution chart of standard sex differences: ● Small difference in means of traits, but LOTS of overlap between sexes o Gender roles ● Sex differences in childhood gender roles ▪ Toy preferences ▪ Sex or preferred playmates ▪ Rehearsal play as caregiver ▪ Interest in infants ▪ Rough-and-tumble play ▪ Physical aggressions (one of the larger sex differences) o Growing evidence that sex difference result from epigenetic process of sexual differentiation o Many differences apparent early in development prior to 'socialization' o Gonadal hormones likely involved in children's gender roles (much of this occurs in utero) o CAH ● Congenital adrenal hyperplasia ● Fetal adrenal glands overactive and secrete high levels of androgens ● Masculization of females ● CAH girls exhibit: ▪ Masculinized toy preferences ▪ Prefer male playmates ▪ "Tomboyism" ▪ Reduced rehearsal play as caregiver ▪ Reduced interest in infants ▪ Reduced interest in physical appearance ▪ Greater aggression ▪ Masculinized childhood drawings ● Consistent with hypothesis that early hormone exposure affects sex differences in personality o Effects of parenting ● Do parents matter at all? ▪ Attachment theory posits a strong determining factor of parenting ▪ Evidence that this link is not very strong ▪ A lot of traits aren't really influenced by parental behaviour ● Social development ▪ Parent offspring correlations have been assumed by SSSM as evidence that parenting is important ▪ Cannot dissociate genetic and environmental contributions ● Shared home ● Shared genes ▪ Mallifert twins - separated at birth, meet later, and realize they share a lot of traits ● Twin studies and pedigrees are classic ways to study behavioural genetics ▪ Broad sense heritability ● When we look at variation in population, how much of it is due to genetic variation? ● Compare monozygotic (identical; 100% shared genes) to dyzygotic (non-identical; 50% shared genes like sibling) ● Look at variation and see to what extent traits are due to genes ● If heritability is high - traits should be more similar in monozygotic twins ● If heritability is low - similarity of traits between mono and dyzygotic twins