Outline Lecture 15 (what follows from mating) Parenting 1
1. Child-rearing in pre-modern societies
o often between 40-50%
o almost 50% of infants did not make it to puberty
o we have been able to conquer most childhood mortality by curing infectious
o infant mortality is creeping back up in some of the poorer areas in the US
there are also conflicts of interest - because they are not genetically
sometimes it's better for them to invest more time in themselves than their
o genes make tough decisions in face of tough circumstances
“Cooperative breeding”: much help from other relatives
Trade-offs revisited: parental effort vs. mating effort
o trade off between
invest in one's self
parental offspring (PI)
NATURAL SELECTION IS GOING TO FAVOUR PSYCHOLOGICAL SELECTION
Are nuclear families typical in small-scale societies?
o It takes a village to raise a child
o Children are cared for by more than immediate family
o In an agricultural society: for children 0-4, taken from observation of all 342
members of village of "Grand Arse" Trinidad
o Cooperative breeders (large family helping to raise new babies (humans share a
lot of that)
o Paternal uncertainty - mothers always know its their kids - dads don’t have the
The more uncertainty he has the less he is engaged with the child
o Hadza men play with their children less when there are more single fertile women
o Humans have bi-parenting
o We are born much more helpless than other mammal offspring
o We stay reproductively immature for many years
2. Grandmother Hypothesis
o Older women can increase RS by switching to investing in grandchildren
o Children without mothers experience high mortality, and maternal mortality
increase with age
o Grandmothers increase grandchild survival and by direct grandmothering
This can result in decreased infant mortality Decreased interbirth intervals
Earlier age of first reproduction
o Older mothers are much more likely to die than younger mothers - as a result the
children are more likely to die. Therefore they help with their grandchildren
They're helping their offspring survive
As well as helping their grandoffspring
Can have kids in a higher rate is the grandmother helps because with
o Grandmothers increase the fecundity and lifetime reproductive success (LRS) of
their daughters (18th century data)
Women whos mothers are alive tend to have more children and more
surviving children than when their mother is dead
o ALSO: cease direct reproduction in order to avoid competing over alloparental
(someone else caring for you) care with ones daughters and daughters-in-law
Why invest so much in grandoffspring?
Chip males prefer older females because the females are better mothers
- Why have menopause (i.e. why cease reproducing when older)?
o Could it be...
Limited number of eggs?
That number would evolve into a high number
This is the proximate explanation
Short lifespan in EEA (environment of evolutionary adaptivness)
This is the average and mask the fact that people do live into their
40's, 50, 60 and even 70's in the hunter gatherers societies
Some oldest individuals don’t even know what they were born
- Switch to caring for grand offspring
3. What is the Optimum Number of Kids?
- How many children? - Whats the optimal number?
o Human females do not maximize number of offspring - Why not?