PSY 544 Lecture Notes - Lecture 10: Meta-Analysis, Observer-Expectancy Effect, Ovulation
• Reproductive variance in men and women
Just to illustrate that
• What is the theoretical maximum number of pregnancies a woman could have? How
many pregnancies can she have implicating how many children can she have
• Theoretically, lets just assume a
• Assuming a reproductive lifespan where fertility begins early from 13-and ends at
50/51 years.
• Assuming the minimal gap (2 months) between one birth and the next pregnancy. Its
impossible to give birth and then immediately get pregnant again as there is a period
after giving birth before ovulation begins again - assuming this gap to be 2 months
we also assume for the purpose of the calculation, no initial increase in fertility and
no decline with age/miscarriages
• Assuming no decline in fertility with age and no miscarriages.
• So if we have
o 38 years of fertility x 12 months = that gives us 456 months and we can only
have a kid every 11 months (9+2=11) so that gives us:
o 456 months / 11 months = 41.45 pregnancies so we get roughly 40 pregnancies
as the theoretical max number
• A more realistic maximum might be about 30. taking in account miscarriages and
time that may take to fall pregnant - it turns out this calculation correspondents well
with the maximum number of pregnancies that a woman has ever had - so the
current world record for the max number of kids that a single woman has had is 69 -
69 kids but only 27 pregnancies and the reason and the reason for this is that this
person have 16 pairs of twins, 7 sets of triplets, and 4 sets of quadruplets but only 27
pregnancies
• Lets take this and - So if you're a woman and you're reproductive variance is b/w 0
and 69 - that’s the ue of kids ou a possil hae - now lets think about
reproductive variance for males - if the minimum is 0 whats the max - supposedly
that jehngis khan had some where b/w 1000 and 2000 kids so the variance for men
is much much larger for men than women
• Reproductive variance in men and women
• Brown et al. (2009)
• Ee i less etee ases, e’s epodutie aiae is/ has ee shown to be
geate tha oe’s.
• Historical records (e.g. Norway, Sweden) and data from indigenous (e.g., Hadza,
!Kung, Aka) populations suggest the following:
find more resources at oneclass.com
find more resources at oneclass.com
• Historical records and data from indigenous records suggest that there is, even now,
a great variance in the number of children b/w men some have no other have lots
than women - the greatest range of variance is in societies where multiple marriages
are allowed
• There is greater variance in the number of children between men (some men have
no children, others have lots) than between women.
• This is true, even in monogamous societies (although less so).
• Why are men more violently aggressive than women?
• We know from studies across species that In the sex with greater reproductive variance,
selection favours taking risks (because risks pay off more, if you have genes that
predispose you to taking risks to acquire whatever it is you need to acquire to get more off-
springs, then selection should create a more risk taking behv amongst the group wehre
that risk taking behv will benefit, so the group with a greater reproductive variance)
• If ou thik of aggessio ad iolee agaist ials it’s a fo of isk
• In the sex with greater reproductive variance, selection favours taking risks to obtain
whatever it is that limits reproductive success:
• Violence against rivals, who directly block your access to members of the other sex
• Acquiring resources, perhaps by violently taking them from members of your own
sex
• In addition, recall that where one sex invests more in offspring, members of the other sex
will show a greater inclination to intra-sexual competition. Remember that across species,
when one sex invests more than the other, the other sex competes more and that intra
sexual competition leads to sexual dimorphism so the example of :
• Recall the Southern Elephant Seals males are larger than females because large size is
beneficial to males in competition with other males for access to females
• The males violently compete with each other to gain territory on the beach. When
territory is acquired, the male gains access to females.
Recall also that males are 5-6 times larger than female, because large size is an advantage
for a male.
Greater intra-sexual competition = more sexual dimorphism.
• A suggestion from evolutionary psychology is Males in our own species may be more
predisposed to violent aggression than females because of a long history of mild but
sustained intra-sexual competition. The risks and rewards are greater in terms of
reproductive output of engaging in intra-sexual competition - intra-sexual competition
amongst males can also involve acquiring resources - so this might explain why violence is
most often committed by men towards other men
find more resources at oneclass.com
find more resources at oneclass.com
• This might explain why violence is most often committed by men, towards other
men.
• And it's not that women don't compete but studies show that women aggression is more
likely to take indirect forms as mentioned earlier Women also compete, although studies
sho that oe’s aggessio is oe likel to take idiet fos deogatio of
competitors, ostracization, recruiting others against them) some have argued that theres
an evolutionary explanation for this - iolee is iske ad does’t pa off ell esp if the
responsibility to care for infants has historically fallen more on women, physical violence
can put you and ur children at risk
• Given the typical care of infants has been conducted by women, physical violence
puts both a woman and her children at risk (Campbell, 1999, 2002).
• Evidence for distinct adaptive patterns of aggression
• There are adaptation in men for physical aggression
• The early onset of aggression in males
• Men seem to have adaptations for greater physical aggression. And we can see this in the
reliable difference in the size of men and women
• Body Differences
• Recall that, across species, there is a reliable relationship such that, greater intra-
sexual competition =/equals greater sexual dimorphism =/ greater aggression. And
we always find across species that if one sex if larger than the other, the larger sex is
more aggressive ex male chimps are on avg are 50% heavier than female chips and
male chimps are more aggressive than female chimps
• Men weigh, on average, about 18% more than women.
• In fact, the sexual dimorphism between men and women is much greater if we
consider muscle mass. Just the sheer weight of individuals doesn't take into account
what that weight is composed of and there's even stronger sexual dimorphism in
muscle mass b/w men and women
• Men seem to have adaptations for greater physical aggression.
• Body Differences
• In fact, the sexual dimorphism between men and women is much greater if we
consider muscle mass.
• Lassek & Gaulin (2009):
• so studies show that
o Men have, on average, 75% more arm muscle mass (and 50% more leg muscle
mass) than women.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
How many pregnancies can she have implicating how many children can she have: theoretically, lets just assume a, assuming a reproductive lifespan where fertility begins early from 13-and ends at. 50/51 years: assuming the minimal gap (2 months) between one birth and the next pregnancy. 69 kids but only 27 pregnancies and the reason and the reason for this is that this person have 16 pairs of twins, 7 sets of triplets, and 4 sets of quadruplets but only 27 pregnancies. If (cid:455)ou thi(cid:374)k of agg(cid:396)essio(cid:374) a(cid:374)d (cid:448)iole(cid:374)(cid:272)e agai(cid:374)st (cid:396)i(cid:448)als it"s a fo(cid:396)(cid:373) of (cid:396)isk. In addition, recall that where one sex invests more in offspring, members of the other sex will show a greater inclination to intra-sexual competition. When territory is acquired, the male gains access to females. Recall also that males are 5-6 times larger than female, because large size is an advantage for a male.
