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Chapter 16

Chapter 16 How Humans Evolved - Bio 1M03.docx
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Department
Biology
Course
BIOLOGY 1M03
Professor
James S Quinn
Semester
Winter

Description
Bio 1M03 How Humans Evolved Chapter 16: Evolution And Human Behaviour Why Evolution Is Relevant To Human Behaviour  The application of evolutionary principles to understanding human behaviour is controversial  All phenotypic traits, including behavioural traits, reflect the interactions between genes and the environment o Every trait results from interaction of a genetic program with the environment o The expression of behavioural traits is usually more sensitive to environmental conditions than is the expression of morphological and physiological traits o Canalized – traits that develop uniformly in a wider range of environments (eg/ finger number)  Can still be modified by environmental factors (eg/ fetal exposure to mutagenic agents or accidents) o Plastic – traits that vary in response to environmental cues (eg/ subsistence strategies) o Every trait, canalized or plastic, result from the unfolding of a developmental program in a particular environment  Natural selection can shape developmental processes so that organisms develop different adaptive behaviours in different environment o People believe that natural selection cannot create adaptations unless behavioural differences between individuals are caused by genetic differences  False  Evidence against – foraging strategies, marriage practices, values – not genetic factors; product of learning and culture Understanding How We Think  Evolutionary analyses provide important insights about how our brains are designed o Humans have large complex brains o Natural selection have made our brains bit and has shaped our cognitive abilities and modified the way we think  Even the most flexible strategies are based on special-purpose psychological mechanisms o Animals are predisposed to learn some things and not others  Eg/ Rats and food aversion  Rats learn to avoid food that makes them ill – base don the taste; not on the size, shape, color or other attributes of the food  Makes sense because they frequently encounter new foods, in novel environments, in the dark  Our brains may be designed to solve the kinds of problems that our ancestors faced when they lived in small foraging bands o Complex adaptations like the brain evolve slowly – brains are designed for life in foraging societies, as humans used to live in small-scale foraging societies o Environment of Evolutionary Adaptedness (EEA) – the social, technological and ecological conditions under which human mental abilities evolved o Foraging groups face problems that affect fitness; food sharing – type of altruism  Humans finely tuned to detect cheaters o If early hominins lived like contemporary foragers – reasonable to think that human brain has evolved to solve problems that confront modern foragers o If lifeway’s that characterize contemporary foragers did not emerge until 40 kya – might not have been enough time for selection to assemble specialized psychological mechanisms to manage the challenges that forages face  Evolved psychological mechanisms cause human societies to share many universal characteristics Inbreeding Avoidance  The offspring of genetically related parents have lower fitness than the offspring of unrelated parents do Bio 1M03 o Inbred Mating’s – mating’s between relatives o Outbred Mating’s – mating between unrelated individuals o Offspring of inbred mating are much more likely to be homozygous for deleterious recessive alleles  Offspring are less robust and have higher mortality o Eg/ Tay-Sach’s, PKU, cystic fibrosis are caused by a recessive gene – heterozygotes are normal, homozygotes are affected – inbred offspring are more likely to be affected o Small frequency of deleterious recessives at eat locus but many loci in the human genome – each person carries the equivalent of two to five lethal recessives on their genome o Inbreeding leads to substantial reductions in fitness o Suggests that natural selection should favor behavioural adaptations that reduce the chance of inbreeding  Mating’s between close relatives are very rare among nonhuman primates o Dispersal may be an adaptation to prevent inbreeding  Adult males leave natal groups near time of puberty – don’t stay long enough to mate with daughters o Natural selection has provided at least some primates with a strong inhibition against mating with close kin o Ex/ Place father with daughter and mothers – do not mate  When an unrelated male replaces the father – mother and daughter mates with male o Inbreeding aversion  Humans rarely mate with close relatives o Domestic arrangements vary greatly across cultures  Some groups are polygamous, some are monogamous, and few are polyandrous  Married couples live with husbands kind, some live with wife’s kin, some set up own households  Some must marry their mothers brothers child – others are not allowed to do so o No documented cases in which brothers and sisters regularly marry, or parent mates with own child  Adults are not sexually attracted to the people with whom they grow up o Childhood propinquity stifles desire – people who live in intimate association as small children do not find each other sexually attractive as adults o Taiwanese Minor Marriage – children were betrothed and the prospective bride was adopted into the family of her future husband during infancy  Betrothed couple grew up together like brother and sister  Partners I minor marriages found each other sexually unexciting – some cases where fathers-in- law had to beat newlyweds to convince them to consummate their marriage  Minor marriages produces ~30% less children than other arranged marriages  Must more likely to end in divorce or separation  Infidelity more common Bio 1M03 o Kibbutz Age-Mates – before WWII many Jewish immigrants organized themselves into communities (kibbutzim) where children were raised in communal nurseries and lived intimately with small group of unrelated age-mates from infancy to adulthood  Few cases of sexual experimentation and marriage were not observed; only occurred between two people, one of which joined kibbutz after the age of six o Third-Party Attitudes Toward Incest -  Coresidence during childhood generates sexual aversions to particular participants  Those who had grown up with opposite-sex siblings had stronger negative responses to hypothetical incest scenarios  Women generally have stronger aversive responses to the hypothetical scenario than men  Evolutionary interpretations of inbreeding avoidance differ sharply from influential theories about incest and inbreeding avoidance in psychology and cultural anthropology o Theory and observation suggest that the family is not the focus of desire; it is a tiny island of sexual indifference Human Language  The cognitive capacities that give rise to language are universal o People speak different languages; but they share morphological adaptations that make spoken language possible and the cognitive capacities that allow them to learn and to use language o The abilities to decode words and to extract meaning from combinations of words are based on highly specialized and derived cognitive mechanisms  Humans can perceive speech sounds at a much more rapid rate than other sounds o Phonemes – basic unit of speech perception; the smallest bits of sound that we recognize as meaningful elements of language o Not all languages recognize the same phonetic distinctions  Eg/ English speakers – can distinguish between “r” and “l”  Japanese and Swahili lump them into one phoneme o Infants can initially distinguish the full range of phonemes – during the first year of life they become insensitive to distinctions that re not part of the language spoken around them o Able to decode very rapid streams of phonemes  We perceive speech as a sequence of discrete-words with brief silences between words, even though this is an auditory illusion  Language is based on grammatical properties that allow us to interpret sequences of words o In order to create meaning, our brain interprets information using rules that specify meaning – rules are called grammar o Unconscious rules that allow people to speak and understand spoken language effortlessly o Universal Grammar Rules  Words must belong to categories such as “noun”, “adjective”, “verb” – which correspond to basic features of the world that people need to talk about  Above:
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