Are the reasons for observed sex differences biologic

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Are the reasons for observed sex differences
biologic?
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What are the physical differences?

• Chromosomal
• Hormonal
• In utero
• Across the life span

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A little biology lesson

• Every cell has a full complement of genetic
  material 23 chromosome pairs (half of each pair
  inherited from mom and half from dad)

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Except for the gametes!

• Gametes are the sex cells (eggs and sperm)
• Gametes only have one set of chromosomes, so that
  when egg and sperm meet, the resulting individual
  has both again!!

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Meiosis
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• The male-specific region of the Y chromosome, the
  MSY, differentiates the sexes and comprises 95
  of the chromosome's length. Here, we report that
  the MSY is a mosaic of heterochromatic sequences
  and three classes of euchromatic sequences.
• These classes contain all 156 known transcription
  units, which include 78 protein-coding genes that
  collectively encode 27 distinct proteins. The
  X-transposed sequences exhibit 99 identity to
  the X chromosome. The X-degenerate sequences are
  remnants of ancient autosomes from which the
  modern X and Y chromosomes evolved. The
  ampliconic class includes large regions (about
  30 of the MSY euchromatin) where sequence pairs
  show greater than 99.9 identity, which is
  maintained by frequent gene conversion
  (non-reciprocal transfer). The most prominent
  features here are eight massive palindromes, at
  least six of which contain testis genes.

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Discussion Points

• This is the only difference between men and
  women. Is it a large one?
• What does Sapolsky say?

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Hormonal Action

• Organizational
• Hormonal influences during critical developmental
  periods that produce relatively permanent changes
  in the organism
• Activational
• Hormones act as triggering influences on the
  expression and performance of behavioral patterns

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Effects of testosterone

• Anabolic effects include growth of muscle mass
  and strength, increased bone density and
  strength, and stimulation of linear growth and
  bone maturation.
• Virilizing effects include maturation of the sex
  organs, particularly the penis and the formation
  of the scrotum in unborn children, and after
  birth (usually at puberty) a deepening of the
  voice, growth of the beard and axillary hair.
  Many of these fall into the category of male
  secondary sex characteristics

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Testosterone production

• Both men and women produce the same androgen, by
  default
• Men produce an average of 7000 micrograms/day and
  convert 1 of it to the precursor to
  estrogen/progesterone (estradiol)
• Women produce 300microgram/day, on average, and
  convert 50 to estradiol

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Influences of testosterone Organizational

• Sexual dimorphism
• The systematic difference in form between
  individuals of different sex in the same species.
• Undisputed sexual dimorphisms in humans include
  gonadal differentiation, internal genital
  differentiation, external genital
  differentiation, breast differentiation, muscle
  mass differentiation, and hair differentiation.
• http//www.virtualffs.co.uk/male.female20facial2
  0differences.htm

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Sexual Dimorphism in Humans

• The basal metabolic rate is about 6 percent
  higher in adolescent boys than girls and
  increases to about 10 percent higher after
  puberty.
• Women tend to convert more food into fat, while
  men convert more into muscle and expendable
  circulating energy reserves.
• Women (on average) are about 52 percent as strong
  as men in the upper body, and about 66 percent as
  strong in the lower.
• Men, on average, have denser, stronger bones,
  tendons and ligaments. Although these differences
  may seem to indicate a natural predilection
  amongst human males for "heavier work.
• Men dissipate heat faster than women through
  their sweat glands.
• Women have a greater insulation and energy
  reserves stored in subcutaneous fat, absorbing
  endothermic heat less and retaining exothermic
  heat to a greater degree.
• Sex differences in endurance events are less
  significant than for sprinting events.

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• Men typically have larger tracheae and branching
  bronchi, with about 30 percent greater lung
  volume per body mass.
• They have larger hearts, 10 percent higher red
  blood cell count, higher hemoglobin, hence
  greater oxygen-carrying capacity. They also have
  higher circulating clotting factors. These
  differences lead to faster healing of wounds and
  higher peripheral pain tolerance.
• Women typically have more white blood cells
  (stored and circulating).
• Women produce more antibodies at a faster rate
  than men. Hence they develop fewer infectious
  diseases and succumb for shorter periods.
• Ethologists have argued that women, interacting
  with other women and multiple offspring in social
  groups, have evolved such traits as a selective
  advantage.
• Almost all examples of sexual dimorphism in
  humans are quantitative, and have some degree of
  overlap.

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• Women generally have a smaller waist in
  comparison to their hips.

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D2D4

• In men, the second digit (index finger) tends to
  be shorter than the fourth digit (ring finger),
  while in females the second tends to be longer
  than the fourth.
• The length of the 2nd finger (index/D2) divided
  by the length of the 4th finger (ring/D4). The
  measurement is taken from the crease at the base
  of the digit.

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• Researchers at the University of Cambridge have
  discovered that the financial traders success
  may depend more on their biological traits than
  on their ability to make rational choices. Rather
  remarkable the finger length of the London stock
  traders appear to be related to the amount of
  their earnings.

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On the Relation Between 2D4D and Sex-Dimorphic
Personality Traits.

• Hampson E, Ellis CL, Tenk CM.Several
  personality traits, including aggressiveness and
  sensation seeking, have been hypothesized to be
  influenced by prenatal androgen exposure, though
  evidence for this proposition is limited. We
  investigated whether individual differences in
  aggressiveness, sensation seeking, and several
  prosocial personality traits can be predicted
  from differences in the 2D4D digit ratio, a
  putative marker of prenatal androgen activity. A
  total of 164 undergraduates (87 men, 77 women)
  completed self-report measures of physical and
  verbal aggression, as well as a standardized
  measure of sensation seeking, and five scales to
  assess empathy, nurturance, expressivity/femininit
  y, instrumentality/masculinity, and
  assertiveness. Two sex-dimorphic tests of spatial
  ability also were included. Men had a lower 2D4D
  ratio than women, confirming the typical sex
  difference in digit proportions. Significant sex
  differences were observed on 10 of the 11
  personality scales purported to show sex
  differences and on both tests of spatial ability.
  The 2D4D ratio was a significant predictor of
  scores on three of the four aggression subscales,
  total aggression, thrill and adventure seeking,
  and total sensation-seeking, in the sample as a
  whole and in women. In men, correlations with
  2D4D were significant only for total
  sensation-seeking and verbal aggression. In both
  sexes, lower 2D4D ratios were associated with
  increased aggressiveness and sensation seeking.
  For the spatial tests, there was no evidence of
  any association with 2D4D in either men or
  women. The 2D4D digit ratio may be a valid,
  though weak, predictor of selective sex-dependent
  traits that are sensitive to testosterone.

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• Some biologists theorize that a species' degree
  of sexual dimorphism is inversely related to the
  degree of paternal investment in parenting.
  Species with the highest sexual dimorphism, such
  as the pheasant, tend to be those species in
  which the care and raising of offspring is done
  only by the mother, with no involvement of the
  father (low degree of paternal investment).

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Influences of testosterone Activational
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• Testosterone Levels as a Trait
• Stability I. Both men and women differ in their
  typical levels of testosterone. Retest
  correlations are .50 over a period of 10 years
  (Booth Dabbs, 1993 Mazur Michalek, 1998).
• Stability II. Although testosterone levels show
  moderate rank-order consistency (see above),
  absolute levels decrease with age after a peak at
  age 20.

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• Heritabilty. Testosterone levels are partially
  genetically determined (heritability 60
  Meilke et al., 1987).
• Consequences. As testosterone is the male sex
  hormone, it is plausible that testosterone
  regulates sexual behavior.
• A study by Dabbs and colleagues examined the
  testosterone levels of over 4000 men in the
  military in relation to their marital status.

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Testosterone and Marriage
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• Married men with high testosterone levels
• were more likely to report hitting or throwing
  things at their wives
• to leave home because of trouble with their
  wives
• to have extra-marital sex
• to get a divorce
• (Mazur Michalek, 1998)

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• Lower testosterone levels in married men have
  been replicated in several studies.
• Gray, Kahlenberg, Barrett, Lipson, Ellison
  (2002) also found that married men with children
  had lower testosterone levels than married men
  without children.
• Burnham, Chapman, Gray, McIntyre, Lipson,
  Ellison (2003) found that testosterone levels of
  men in a committed relationship were more similar
  to those of married men than unmarried men.

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Theory So far the evidence has been
correlational. What do you think is the causal
explanation for the negative correlation between
divorce and marital stability? A. Women prefer
men with low testosterone levels. B. High
testosterone men are unhappy in monogamous
relationships. C. Being married lowers a mens
testosterone levels. D. A third variable (e.g., a
shared genetic disposition) has independent
effects on testosterone levels and marital
stability?
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What is cause and what is effect? Trait
theory It is easy to interpret the data as
evidence that testosterone level is a cause of
stable marriage and divorce. (Mazur Michalek,
1998, p. 317). Alternative explanation Mate
theory Getting married lowers testosterone
levels to enable a man to stay faithful to the
mate who is the mother of his children.
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Change from Divorced to Married
Not Married
Change from Married to Divorced
Married
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• Conclusion
• The study replicates other findings of
  differences between married and non-married mens
  testosterone levels.
• The study also shows first evidence that
  testosterone levels change with marital status.
  This finding supports the mate theory.
• Stable married men had lower testosterone levels
  than men who married during the study. This
  finding provides some support for the trait
  theory.

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• General Conclusion
• Testosterone levels are correlated with marital
  status.
• High testosterone levels may be a risk factor
  for having a stable, faithful marriage.
• A stable, faithful marriage may be a risk
  factor for low testosterone levels.
• Future research needs to examine how
  testosterone levels influence actual behaviors in
  marriages.

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• Hormones An Afterthought
• Hormones primary function is to communicate
  between the brain and peripheral organs.
• Concentrations of hormones in the blood are
  unlikely to be strongly related to the brain
  processes that regulate behavior, feelings, and
  thought.
• Research on the biological processes in the
  brain are going to be more important for the
  understanding of personality.

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No one disputes that there are physical
differences between men and women

• The controversy arises when we attempt to
  establish links between the biological
  differences and the behavior of men and women
• It is further inflamed when we attempt to justify
  social structures on the basis of the differences
  (sexism).