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A Mind Of Her Own By Anne Campbell Annie Greynald Dana Stewart Keah Larsen
Sexual, not natural selection § § § animal that survives but doesn’t reproduce leaves no genes behind sexual selection: the advantages which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction. ’ genes enhancing good reproduction will flourish even if earlier death is result
Sex differences derive from sexual rather than natural selection n genetic trait increasing the number of children reared will be passed on n n but the traits assisting these genes are different in men and women such genes may be activated by sexspecific hormones, thus men and women show different expressions of these genes.
Anisogamy: the start of parental inequity n advantages of parthenogentic species n n n 1. 2. 3. 4. no time wasted looking for a mate no exposure to predators while copulating no concern of desirability don’t sacrifice 50% of genes advantages of sexual reproduction (mating) n n n 1. unique individuals 2. less competition 3. increase odds some will survive environment with unique immune systems
Why an egg and sperm? n n mutations and variability occurred in gamete size, some giving more or less than half of their chromosomal information those who gave less, produced more & those who gave more, produced less n n sperm and egg large gametes good for egg because they must carry nourishment for growing zygote to survive small gametes good for sperm because they are small, cheep and mobile medium gametes had neither advantageonce anisogamy began, the gulf between only became larger
Robert Trivers n n n key reproductive difference between sexes = parental investment r-k selected distinction holds for men and women minimum biological costs of reproduction are much greater for females 20 eggs/month vs. 300 million sperm/ejaculation by the time baby arrives, mother views offspring as huge emotional and physical investment
Sex differences result from the female’s greater biological investment compared to men n n psychological differences are side-effects men have plenty of time to desert female while she develops the ovum for 9 months desertion leads to future reproductive prospects women have no benefit from desertion of a male
Why such a long period of parental care? n n n 9 months is a compromised gestation period later than 9 months the head becomes to big to fit through pelvic bones earlier than 9 months, offspring would be too immature to survive
However, babies are still born too early in a maturational sense n n they are completely dependent on parental care women will provide more parental investment because infant represents huge biological investment
Man and the attraction of polygny n n n ideal condition for reproductive success is access to many fertile females evolution has fitted men for polygny to enhance reproductive output evidence for this derives from examining sex differences
Why Men Invest at All n n n Need for additional parental care Paternal certainty Behavior of females
Need for Additional Parental Care n n How important is paternal care to the survival of the infant? Is it more beneficial in terms of reproductive success to invest? n Evolutionary past show a high correlation between father abandonment and child mortality.
Paternal Certainty n n The greater the doubt the less willing is the male to invest Internal fertilization and concealed ovulation make it harder for the male to make certain of paternity. n mate guarding has evolved as a means to lessen this uncertainly
Behavior of Females n Rewarding Monogamy n n Females should encourage monogamy by practicing fidelity. Discouraging polygyny n Females should make it difficult for men to take part in a polygynous mating system. They can do this by being less willing to have casual sex and by patronizing women who do so.
Women as choosy investor n n n Environmental Factors Quality of male mate More parental investment
Environmental Factors n n Females must ensure that her body has a reasonable chance of sustaining the pregnancy Suppression or even loss of menstruation is very common in environments of poor resources and high stress n n Stress is relative Babies are more likely to be born during seasons when the climate is moderate and food supplies are plentiful.
Picking the right mate n Concealed ovulation n Creates uncertainty about who the father is. This way the woman can fool each man into believing they are the father and so encourage them to supply recourses and defense. This will make for a more likelihood of infant survival. Encourages monogamy. The male must go through a period of courtship in order to ensure that she has not and is not copulating with other males. Evolved as an advantage for women
Picking the right mate … n n Favoring healthy and attractive males “sperm wars” n n Only the most successful sperm with the strongest army will win and therefore impregnate. Female orgasm n n Increases the likely hood of conception More likely to occur when the female has strong feelings about the male.
More parental investment n n The decision to investment in a child must be made carefully There are many points at which a lessthan-optimum pregnancy can be knowingly or consciously halted.
More Parental Investment n Only a very small percentage of fertilized eggs make it through the first trimester n n n Low success of implanting Miscarriages Concord fallacy n If an infant is not viable than a woman is better off abandoning it as early as possible.
Abortion n Voluntary abortion is high among young women ages 20 of less. n n n ¾ is 18 -19 year-olds choose to terminate their pregnancy. Material, personal and intrapersonal resources also play a role in the decision to abort. The best predicator of abortion is whether the father is willing to commit himself to the mother n In the United States 65% of pregnancy among unmarried woman were terminated compared to the 10% among married women.
Abortion n Another factor is the woman's own psychological stability. n In addition, these women have a more likelihood of miscarriages and are also more likely to give birth to infants with health problems.
Infanticide n Infanticide is a last resort for a woman who believes that the investment in the current infant is not worth continuing. n n Factors in deciding to commit infanticide include deformity of the infant at birth, absence of male support, and economic hardship Post-partum depression: a psychological adaptation that reduces attachment and may thus open the way to infanticide. n associated with inadequate emotional and material support from the father, family, and friends.
Women As Heavy Investors The birth of an infant is only the beginning of the mother’s duties, not the end.
Orphaned Infants n n To ensure the survival of her offspring, a mother must defend and feed her infant(s) and herself. The disappearance or death of the mother dramatically shortens the life expectancy of an infant. When a mother initially disappears, the effects in the infant are observed immediately in the rise of stress activated cortisol levels. Long term disappearance of the mother most often causes a shortened life-span for the infant. n n Jane Goodall observed this in the infant primate Flint. A North-western German coastal region have records that prove this phenomenon in humans.
The Importance of Lactation for Mother and Infant n n n In a mother, breast feeding suppresses ovulation, thus causing a better spacing between children. In infants, breast milk provides about half a gram of anti-bodies a day. For both, it is a pleasurable experience because of the release of oxytocin in the mother which is passed on to the infant.
The Bond Between Human Mother and Infant n n n Within 48 hours of birth, mothers can distinguish the cry of their own infant. Human mothers are able to distinguish between a distress cry and a hunger cry from a baby. As early as 2 months, the infant is able to show a negative response to strangers. n n An evolutionary force is behind an infant’s fear of strange males instead of females. When upset, most children prefer their mother over their father to provide comfort.
Child Care n Even in this liberal era, mothers do most of the routine childcare. n n In traditional and non-traditional families, mothers proved to be more affectionate, soothing, disciplining, and vocal towards the infant. n n In households where both parents work, such as Israel and Sweden, mothers return home and carry out a majority of the duties. The amount of child-care and play between father and child depends on the relationship between father and mother. When Divorce occurs, the mother almost always takes on the child-care responsibilities. n In no state do mothers abandon their children at the rate fathers do.
Pursuing Half The Point The pre-occupation with mating studies and the neglect of parenting studies.
Male and Female Roles n n Males devote their time to finding the right mate, females devote their time to raising the offspring to maturity. Parenting is critical to the survival of the offspring, perhaps more than finding the right mate, however a woman’s role is seen by many researchers as “unproblematic”. The excitement of the pursuit of a mate is perhaps why more research is devoted to mate selection over parenting. The excessive study of male-male competition only confuses the fact that males competed because they were much less important. n A loss of females would be much more hazardous to the human population than the loss of males.