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Families Overview of the Day What is a family? Evolutionary perspective Family conflict mother-fetus, mother-infant, parentchild, sibling Altruism and inclusive fitness Discussion of class projects What is a Family? Why did Families Evolve? Groups where offspring continue to interact with their parents regularly into adulthood simple families (nuclear) extended families Only 3% of bird and mammalian species form families what are the benefits and costs? Mother-Fetus Conflict Over Mother’s food Pregnancy sickness: nausea, vomiting, and food aversions and cravings during pregnancy Functions of pregnancy sickness prevent fetus from being exposed to teratogens (toxins that are harmful to developing fetus) Pregnancy sickness is associated with: Fewer miscarriages Fewer fetal deaths Food Aversions and Cravings Aversions Meat Vegetables Beverages containing caffeine (coffee, tea) Cravings Fruit and fruit juice Sweets Grains and starches Dairy and ice cream Mother-fetus Conflict over Mother’s Blood Supply Placental cells destroy arteriolar muscles which regulate blood supply and secrete substances that increase constriction of arteries Constriction results in: more blood to fetus but high blood pressure to mom (excessive HBP--> preeclampsia) Moderately HBP during pregnancy is associated with lower fetal mortality Mother-Fetus Conflict over Mother’s Glucose Fetus secretes hPL (human placental lactogen) that ties up mother’s insulin Mother’s glucose goes up, providing more to fetus Mother then secretes more insulin and fetus secretes more hPL If mother cannot respond with enough insulin, she develops gestational diabetes Conflict over Weaning Who wants to cease weaning first, mother or infant? Why Sibling Conflict 50 % relatedness Compete with each other for resources MZ twins exhibit less conflict Half sibs exhibit more conflict Why do parents teach children to share? What hurts your relative hurts your fitness Other Conflicts Finicky about food Adult and child nutrition needs are different Children more susceptible to teratogens Bedtime Night was dangerous, safer with mom Higher incidents of SIDS among children who sleep alone Parents and Teenagers Adolescent rebellion Changes in frontal cortex Develop own identity Perhaps a motivating force for leaving the nest Can you think of possible evolutionary explanations for the reckless behavior of many teenagers? Kin Selection and Hamilton’s Rule Kin Selection: Altruism toward kin Hamilton’s Rule: Natural selection favors mechanisms for altruism when c < rb where c = cost to actor r = relatedness of actor and recipient b = benefits to recipient Another relevant variable is reproductive value, v. Altruism and Inclusive Fitness Altruism: helping other without consideration of one’s own welfare Inclusive fitness: the number of copies of one’s genes that appear in current or subsequent generations of offspring and kin’s offspring Altruism increases inclusive fitness Who Would You Help? Jump in a river to save ___ bothers ___ cousins 1 < .5(3); 1 < .125(9) How about a non-relative? Reciprocal altruism: giving help with the expectation that the other will return the favor in the future (tit for tat). Evolutionary stable strategy Who do People Help the Most? Ground squirrel alarm LA study: help was a linear function of relatedness Studies of wills: 92.3% of people leave money to kin Who helps more: maternal or paternal uncles and aunts? The Grandmother Hypothesis Why do women live beyond menopause? They contribute substantially to the welfare of grandchildren Grandmothers share 25% of their genes with their grandchildren Altruism in The Road North What concepts from EP could explain why Claveles Picero gave her young son to Senora Dermoths’ charitable mission? What concepts from EP could explain why Jesus Picero was so insistent that they travel 70 kilometers to look for his grandson? Why did the mother of Jesus’ youngest son’s daughter drop her (the daughter) off in a bundle on the father’s barracks door? The Evolution of Marriage and the Benefits of Marriage Why does the institution of marriage exist in every society, and why has it existed for thousands of years? It works--not perfectly, but better than alternatives devised so far Child rearing and paternity uncertainty Other benefits: married adults are less likely than single adults to die young, develop physical disabilities, or suffer psychological and emotional illnesses Summary and Projects What is a family? Family conflict Altruism and inclusive fitness Your projects: Focus Question that can be addressed with data What type of data will you collect? How will your data answer your question?
