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1. Relationships PSYA3: Part 1 AIMS AND OBJECTIVES Ref Content Notes? Understand? Revised ? part Human Reproductive Behaviour 1 IDENTIFY AND EXPLAIN The relationship…
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  • 1. Relationships PSYA3: Part 1 AIMS AND OBJECTIVES Ref Content Notes? Understand? Revised ? part Human Reproductive Behaviour 1 IDENTIFY AND EXPLAIN The relationship between sexual selection and human reproductive behaviour including evolutionary explanations of sex differences in parental investment. (eg sex differences, parent-offspring conflict). SAMPLE QUESTIONS 1) a) Outline evolutionary explanations for human reproductive behaviour (9) b) Critically assess these explanations (16) 2) a) Describe sex differences in parental investment (9) b) Assess the implications of these sex differences in terms of human parental investment (16) Why do some tortoises have long necks? From the PTCC book Part of getting to grips with evolutionary theory is getting to grips with the terminology – using each word in the table once, see if you can fill in the gaps below. Consider the three tortoise ______________that inhabit the Galapagos Islands. They are quite similar but each species has unique__________________. How did this happen? The theory of evolution proposes that there was a common _________________whose offspring migrated to each island. In each new generation new characteristics appeared, some of which are more __________________to the demands of the different environments. For example, one individual on one island may have had a longer neck than other individuals on the island. This made it easier for that individual (and its offspring) to reach tall vegetation. If tall plants were plentiful on their island (because few other animals were eating them) then a longer neck was a valuable characteristic. Individuals with longer necks were more likely to survive and _______________successfully. Testuda abingdonii has a particularly long neck. Individuals of this species have evolved so that they ‘fit’ a particular environmental ________________. On other islands the _________________for long necks may never have appeared (and therefore couldn’t be selected) or the tortoises living on other islands did not experience the selective __________________for long necks (because, for example, there were no tall plants or other animals were eating them) and thus this characteristic did not evolve. Only in situations where a characteristic (1) appears (2) is genetically __________________and (3) is adaptive (i.e. helps the individual to adapt) will it be perpetuated through natural selection. Evolution is sometimes described as ‘survival of the_______________’ meaning those individuals who fit a part of the _________________(a niche). In fact it is not survival that is crucial but reproduction. An individual that survives but does not reproduce does not pass its genes onto the next generation and therefore the selected characteristic does not become___________________. characteristics gene transmitted adaptive perpetuated pressure ancestor environment reproduce species fittest niche PSYA3: RELATIONSHIPS 1
  • 2. Human Reproductive Behaviour- GLOSSARY The following definitions may help you through our journey of the evolution theory The Evolutionary Psychology article written by Lance Workman is also a good reference point for key concepts Adaptation Any feature of an organism that has been shaped by natural selection to enhance its chances of survival or reproductive success of an organism. Anisogamy The difference in size and mobility between gametes (sex cells) of different sexes. Environment of Refers to the environment in which we evolved in, therefore human behaviour has Evolutionary been adapted for the prehistoric environment of when our ancestors were hunter- Adaptedness (EEA) gatherers on the African savannah between 35,000 and 3 million years ago. Evolution In biological terms is the process by which new species arise as a result of gradual changes to the genetic-make-up of existing species over long periods of time. Gamete Sex cells contain the same amount of genetic information: males produce small motile gametes called sperm (produced in very large numbers - 100 million per day) and females produce large immobile gametes called eggs which have a store of energy to assist embryo development (make fewer in a lifetime - 450 eggs). Inclusive fitness Total number of an animal's genes present in subsequent generations. These genes will be present in direct offspring and in the offspring of close relatives such as brother or sisters. Inheritance When a feature in the offspring resembles that in the parent. Intra-sexual selection Competition between members of the same sex Inter-sexual selection Competition between members of different sexes. Mutation Birth of a new gene, can be good or bad. If it increases survival chances it is more likely to be passed on to offspring. Natural selection Suggests that all animals are subject to selection according to the environmental conditions that exist at the time. Inherited traits that enhance an animals reproductive success are passed on to the next generation and thus ‘selected’, whereas animals without such traits are less successful at reproduction and their traits are not selected Parental Investment Any investment by the parent in an individual offspring that increases the offspring’s chance of surviving (and hence reproductive success) Sexual selection Depends on the advantage which certain individuals have over others of the same sex and species in terms of reproduction. It’s used to explain features which help to make animals more attractive to the opposite sex for reproductive success Sexual Dimorphism Refers to the different physical characteristics of females and males of the same species e.g males 20% taller than females. Variation Differences within the same sex Make notes on any other key terms that you encounter during this topic PSYA3: RELATIONSHIPS 2
  • 3. Natural and Sexual Selection Task 1: Go on to the following websites and make notes on Natural and Sexual Selection http://evolution.berkeley.edu/evosite/evo101/IIIE3Sexualselection.shtml http://pages.towson.edu/scully/sexual_selection.html Task 2: Answer the following questions using PTCC page 170 a) In our evolutionary past, what happened to men who selected mates low in reproductive capacity? b)Why are women more choosy about whom they mate with according to the evolutionary theory? And what is the term used for this female choosiness? c) What is intrasexual competition? d) According to the evolutionary theory why does it pay to be choosy? Evolutionary theory suggests that there are two main mechanisms for the evolution of an animal’s characteristics: • Natural selection (survival of the fittest). This is the process by which animals that are best adapted to their environment (fitness) are more likely to survive. • Sexual selection (survival of the sexiest-reproductive success). This is the process by which animals that are most successful at mating and having offspring are more likely to pass on their genes to the next generation. It is important to realise that the characteristics that increase an animal’s fitness in terms of natural selection are not necessarily those that increase its chances of reproductive success. In some circumstances the characteristics that increase reproductive fitness might actually endanger and organism. Sexual Dimorphism Sexual dimorphism means ‘a difference in form between the sexes’. It is a term that describes the fact that in many (but not all) species of insect, bird mammal, reptile and so on, the males and females look different. Here are some examples. Label the male and female, and briefly outline the nature of the sexual dimorphism in each. What seems to be the usual pattern in sexually dimorphic species? PSYA3: RELATIONSHIPS 3
  • 4. What does this pattern imply about which sex does the competing and which sex does the choosing where it comes to mating and reproduction? Do you think the same is true of humans? Sexual selection and human reproductive behaviour. What is sexual selection? Intra sexual Inter sexual Criteria of mate selection: Selection for indicators Viability- survival Fertility-reproduction Selection for provisioning Sperm competition Consequences of mate selection: Sexual dimorphism Facial preferences/Body shape and size Human genitalia and orgasm Differences in mate choice Males- (physical attractiveness) Females- (resources) Parental investment theory: Maternal investment Paternal investment Parent-child conflict (research yourself) The origins of mate choice: Mate choice is a product of mate preferences formed in the ‘environment of evolutionary adaptiveness’ (EEA). Our ancestors evolved neural adaptations that favoured mating with those individuals possessing particular traits (such as relative hairlessness). Mate choice among modern day human operates by rejecting some potential mates and accepting or soliciting others. But why did these mechanisms of mate choice evolve in the first place? The fundamental principle of mate choice is that it pays to be choosy because the genetic quality of your mate will determine half the genetic quality of your offspring. By forming a joint genetic venture with a high quality mate, one’s genes are much more likely to be passed on (Miller, 1998). The criteria of mate selection: -Selection for indicators ‘Good Genes’ Indicators of Viability (likelihood of survival)-Handicap hypothesis ‘Good taste’ Indicators of Fertility (likelihood of reproduction)- Sexy Son hypothesis -Selection for provisioning ‘Good sense’ Male provisioning is useful for females because it increases their resource budget and so eases the burden (in terms of nutrition and energy expenditure) -Selection for sperm competition PSYA3: RELATIONSHIPS 4
  • 5. ‘Compete for fertilisation’- In many species, females mate with more than one male during a breeding season, so ‘sperm competition’ is an important factor in determining which male is successful in fertilising her egg. Males do not compete for females, they compete for fertilisation. PSYA3: RELATIONSHIPS 5
  • 6. Male produce sperms in thousands at relatively little physiological cost. Therefore their best strategy is to mate with many females, because this should result in the maximum number of offspring to perpetuate their genetic line. The consequence of anisogamy and the fact that it is the mother who bears the majority of the huge biological cost of producing offspring, is: INTRA-SEXUAL SELECTION: (‘Intra’ means ‘within’)- Males compete with other males for the right to fertilise females (be chosen by the female) INTER-SEXUAL SELECTION: (‘Inter’ means ‘between’)- females exercise choice and select the best male available There are generally fewer sexually receptive females than males in any population and therefore there is competition between males for the scant resource. One strategy for males to compete with other males is called ‘SPERM COMPETITION’. Summarise what is meant by Sperm Competition using PTCC page 170 Evidence: colour the evidence AGAINST INTRA SEXUAL SELECTION Baker and Bellis (1995) support the view that humans are promiscuous than monogamous. They suggested a worldwide median rate for misattributed fatherhood (where the presumed father turns out not to be related genetically) of 9%. artners. E-Poll (2003) survey found that 29% of those interviewed reported having an affair. Women are promiscuous and seek out variety as this increases reproductive potential. However the majority did know who the father was and the majority were not adulterous which challenges the concept that human nature is promiscuous. Females can also be very competitive Size dimorphism: According to Darwin, dues to sexual selection males tended to be bigger and to have greater physical strength. This could be because………………………………………………………………………………………………… Dimorphism is evidence of competition as it suggests that males fight for access to females Sneak copulation: The fact that males compete for dominance is supported by non-human animal hierarchies, which show less dominant males engage in secretive copulation when the dominant (alpha male) is not looking. Some male elephant seals pretend to be females so they can join the harem. PSYA3: RELATIONSHIPS 6
  • 7. Females are not as eager as males to have sex. So they are choosy. But on what basis? INHERITED CHARACTERISTICS: MAKE notes from the textbook “GOOD TASTE” “GOOD GENES” NON-INHERITED CHARACTERISTICS “GOOD SENSE” Evidence: find some evidence for and against this theory For: Against: PSYA3: RELATIONSHIPS 7
  • 8. Consequences of Sexual Selection in humans : USE PG 648 and 649 ‘Psychology a new introduction’ Summarise differences in how male and females evolved because of sexual selection using class text books e.g. penis size e.g. symmetry, WHR etc…. We’ve looked at how the characteristics that men and women find attractive could be related to evolutionary factors. One of the points that comes out of this is how physical characteristics like a woman’s relatively low waist to hip ration are a sort of genetic ‘con trick’ e.g. by hiding when she is most fertile, the woman can ‘con’ men into giving up resources. Evolutionary psychologists sometimes argue that fashion is simply an extension of this evolutionary con trick. Below are some examples of male and female fashions from history and present. For each one, suggest how it might function in an evolutionary sense to make the wearer more attractive as a mate. . PSYA3: RELATIONSHIPS 8
  • 9. http://www.bbc.co.uk/science/humanbody/mind/surveys/lonelyhearts/morescience_lonelyhearts.s html More Science About Lonely Hearts- Read between the lines If you’ve never considered searching for a date in the lonely hearts columns, count yourself lucky. It’s a jungle out there and that’s scientific fact. Are lonely hearts columns a window into our evolutionary past? Enter the world of lonely hearts and you take a trip back through your evolutionary past, where the veneer of civilisation is stripped away and men and women are slaves to their most basic instincts. The frank vocabulary of the ads illuminates the rules of human mating in the most unambiguous way. If you’re a blonde, attractive, curvaceous female, that’s exactly how you should describe yourself in your ad. The same applies if you’re a handsome, athletic, millionaire male. For this very reason, lonely hearts may give us a unique insight into the reasons for our sexual preferences – preferences that have been moulded by millions of years of natural selection. Column inches Professor Robin Dunbar of Liverpool University spent much of the latter half of the 1990s studying the hidden evolutionary signals contained in Lonely Hearts advertisements. quot;We were studying 19th century folk [love] songs, but it wasn’t working out as well as we had thought. Many folk songs are political when you scratch beneath the surface,quot; explains Dunbar. quot;When we changed our focus to Lonely Hearts, we found a close link with evolutionary preferences,quot; he adds. The language of love Dunbar found that the vast majority of words used by people to describe themselves in ads could be lumped into five different categories. He asked 200 university students to rate the appeal of ads containing different categories of words. When Dunbar analysed the results, he found that men and women attached very different levels of importance to the five categories: Men's preferences Women's preferences Far from being conditioned to regard these things as important, Dunbar 1= Attractiveness 1. Commitment argued that men and women had evolved these preferences over 2= Commitment 2. Social Skills millions of years of evolution. These were crucial qualities that 3. Social Skills 3. Resources enhanced the fitness of children, and, lest we forget, children are the 4= Resources 4. Attractiveness key to the survival of our species. What hidden messages do we send the opposite sex? 5= Sexiness 5. Sexiness Pregnancy and breast-feeding place great stress on a mother, so females make the biggest investment in reproduction. This is why women are choosier about their partners than men, with 20-something women being the choosiest of all. This big parental investment also explains why women seek males who are willing to stick around and provide for children. Diamonds are a girl's best friend But evolutionary theory tells us that resources should be just as important to women, if not more so. Good fathers need to have the means to feed offspring as well as the willingness to stick around. In our evolutionary past, before resources meant a Rolex watch and a sports car, a well-heeled man was one with high status in a hunting tribe. High status males were often good hunters and likely to provide a steady supply of food. When the desire for reproduction is taken out of the equation, preferences change drastically. Dunbar has shown that lesbians were three times less likely to seek resources than heterosexual women. But why should such an intangible quality like social skills score highly with heterosexual women? Dunbar puts this down to the Scheherazade effect, a phrase coined by cognitive psychologist Geoffrey Miller. The Scheherazade effect refers to the possible tactics used by ancestral women to appeal to a man’s conversational skills in order to keep them around. Research conducted by Professor Doug Kenrick at the University of Arizona seems to support this sexual dynamic. Kenrick has found that both sexes regard social skills as important, particularly a sense of humour. But that a good sense of humour has a different meaning for women than it does for men. quot;When women look for a sense of humour in a man, they're saying: 'show me what you've got'. But when a man looks for a sense of humour in a woman, they're saying 'she laughs at my jokes, she must think I'm a great guy'.quot; Playing the field The very fact that men need an incentive to stick around leads us to the question of male priorities in the mating game. Men, like women, want to maximise their contribution to the gene pool by having as many offspring as possible. But for males, time spent providing for a pregnant partner could be better spent fathering other children with other women. This may explain why men place such a high premium on attractiveness. Attractiveness is a rough indicator of age, and in women, age is a good indicator of fertility. After her late 20s, a woman's fertility steadily declines, and so does her value on the dating market. PSYA3: RELATIONSHIPS 9
  • 10. Evaluation of Evolutionary explanation of human reproductive behaviour- a02/a03 Universality – Extrapolation – Determinism Reductionism – Ethical issues – Negative View of Humans – Individual differences- PSYA3: RELATIONSHIPS 10
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