Module 10 Flashcards
Parental investment figures into all 3 life history tradeoffs
- Offspring quality vesus quantity
- Investment in current vs. future reproduction
- Mating effort versus parenting effort
Parental Care in Humans
- Human children are expensive
~ Large body size and brain size
~ Born relatively helpless compared to apes, brain underdeveloped
Altricial
- infants are helpless and immobile at birth, require long-term nourishment and other care in order to survive
Precocial
- infants are mobile at birth and other senses are well-developed
Humans are considered secondarily altricial
- because we are born more helpless than other primates
Parental Care in Hunter-Gathers
- Babies spend the majority of time in direct physical contact with a parent
- Babies sleep with parents
- Babies breast-feed for 3-4 years
- Babies breast-feed on demand
Bi-parental care (care by both parents)
- Considered a fundamantal adaptation for human reproduction
~ For reproduction to proceed successfully at its “normal” pace (one child every 3-4 years) in hunter-gatherer conditions, care from more than one parent is necessary
Male care
- Care by males increases offspring survival at the cost of increased opportunities to bear offspring with new females
- Across species, males care is most often seen under 2 conditions
~ It is crucial to offspring survival
~ Paternity certainty is high
IN humans, we can distinguish two types of care
- Direct care
- indirect care
Direct care
- Carrying, play, babysitting, feeding. ACtivities that are done specifically for the child
Indirect Care
- Providing resources. Involves activitied (hunting, wage earning) that benefit the child but do not require direct interaction
Subsistence and Paternal CAre
- hunter-gatherer dads provide intense direct care to offspring, in addition to provisioning
- Once men can accumulate wealth, it becomes easier to “provide” indirectly
- This is also associated with degree of polygyny. Wealth increases ability to care for multiple families. Increases incentive for mate seeking at the cost of direct care
How high is paternity certainty in human males
- In cases where a man has a reason to believe he is the father approximately 2-5% cross-culturally
- Sexual division of labor contributes to paternity uncertainty becasue couples are separated for long hours
- This is a low rate compared with other species
- Investment efforts is very high, so this small amount amtters
Males are more likely to invest of
- The child is known to be theirs
- The child resembles them
- The mother is thought to be faithful
Testosterone
- is key mediator of the trade off between parenting effort and mating effort in males
~ High elevated in mating efforts
~ Testosterone levels drop when they are parenting or with a partner
~ Testosterone stays lower if the man spends more time with the child
~ Testosterone stays high in men who are polygynously married = high mating effort
~ Testosterone is lower in men who provide direct care, not affected much in men who provide only indirect care
Oxytocin
- mother are hormonally primed to invest in new infants
- Hormone oxytocin is released during childbirth and during breastfeeding
- Across a range of species, oxytocin is essential for bonding between mother and infant
- Released when a mother has physical contact with infant or hears her own infant’s cry
- Neurological pathways for oxytocin are influenced by early environments
- Postparum depression associated with reduced ozytocin response to offspring
- May be affected by nursing practices
Parent-offspring conflict
- Mother is related to child by 50%
- Mother is related to other offspring by the same amount
- Child is related to itself by 100%
- Child wants maximum resources for itself
- Parent wants offspring to survive, but wants to balance investment
- Examples
~ Weaning conflicts - mothers usually want to wean offspring before offspring are willing
~ Placenta - the fetus produces hormones that manipulate the mother’s metabolism in its favor.Gestational diabetes and preeclampsia can result
~ Crying - Infants are selected to give cries that imply need to elicit preferential care
When to terminate investment
- Offspring is likely to thrive without it
- Offspring is unlikely to survive
- Future reproductive prospects are good
Mother Nature (A history of Mother, Infants and Natural Selection by Sarah Blaffer Hrdy) (Mother and other by Sarah Blaffer Hrdy)
Books that I might want to read later on in life
Infanticide
- In a large number of species, infants are killed by male non-fathers or (rarely) by female non-mothers
- Humans are exceptional in that the majority of infant killing are preformed by the mother herself
- Infanticide is an extremely common, and often non-taboo, occurrence in traditional societies
- It is common for infants not to be considered human being until they have a been named (which can be 2 or more years)
Most common reasons for infanticide
- Lack of paternal figure ~ Woman unmarried or divorced ~ Husband dead or at war - Inadequate resources ~ Twins ~ Economic hardship ~ Born too soon after previous child ~ Too many children - Inappropriate paternity ~ Incest ~ Adultery ~ Remarriage- infant sired by previous husband - Signs of poor infant quality ~ Deformed ~ Small ~ Ill ~ Rear appearance
19th century Europe
- Maternal workload low, leads to high fecundity
- But financial resources often insufficient to care for children
- Made worse by trend of artificial milks and “wet nursing” by hired girls. Lifted the influence that lactation has on maternal fecundity
- Very successful practices for the wealthy, difficult for the poor
Foundlings
-Milan
~ 343,406 children abandoned between 1659-1900
~ In 1875: 91% of illegitimate children abandoned
- Moscow
~ 1880-1889: 15,475 infants abandoned each years on average
- Florence
~ 1840s, 43% of baptized infants abandoned
Consistently
- cited for the same reasons as infanticide
~ Especially, lack of a paternal figure, inadequacy of resources
“At risk” women are more likely to be pro-choice
- As are members of their families
- As are their political constituencies
- Irrespective of their religious affiliations
Sex-biased investment
- When males resources are unevenly distributed, males have high variance in reproductive success because the have secure more mates
~ Very successful men + many wives and children
~ Leves many men with zeros reproductive success - Females have a high chance of marrying/ reproducing but little variance
- A successful son will yield many more grandchildren than a successful daughter
Sex Biased Investment in India
- Caste system
- Women must marry up in social class = hypergyny
- Brides must bring a dowry appropriate to social status
- Males can have multiple wives
China
- One-child policy promoted selective abortion and abandonment of females infants (1979-2015)