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Transcript of Alloparenting
Michael Romano Alloparenting Alloparenting in Humans Specific Behaviors Grandparenting Humans are Special Secondary Altriciality Economics Infant Transport Allomaternal Nusring The notion that aging women gain an inclusive fitness advantage from investing in their grandchildren (Peccei 2001a)
Inclusive fitnesss advantage- Under the kin selection hypothesis, helpers provide allocare for related infants when it increases kin survival, which in turn increases the helper’s inclusive fitness Menopause is the irreversible cessation of fertility in all women of the species that occurs before the end of the average adult lifespan (Peccei 2001)
Only humans and one species of toothed whale that fit the definition of menopause (Peccei 2001) chimpanzees and rhesus monkeys have shown reproductive declines (Pavelka & Fedigan 1991)
Most primates and even elephants and reproduce in old age (Peccei 2001) When mothers had new babies they foraged less, which was compensated for by the increase in foraging by grandmothers in order to provision for already weaned offspring (Hawkes et al. 2001).
Among the Hadza, post-menopausal women earn the same foraging rates as younger females, and these foraging efforts are linked to the nutritional welfare of their grandchildren (Alvarez 2000). Grandmother care could be a solution in human evolution to the increased dependency of human infants.
Do you agree?
A solution, or a cause? Babysitting Provisioning Food Humans provide more allocare from more individuals Homosexuality Sibling Care Labor Supply of Mothers
Alloparents for Consumption
Formal vs. Informal Alloparenting
Are one or both of these examples of reciprocal altruism?
Is there an economic reason for alloparenting in other animals? Reciprocal Altruism:
the reciprocal exchange of benefits between non-kin (or without the consideration of kin ties)
(Muroyama 1994) Patas Monkey exchange grooming for the right to allomother
For Marmosets and Tamarins who allomother, their infants later receive allomothering from the initial beneficiaries.
Capped Langur females form cooperative alliances among non-kin that in which allomothering is reciprocated.
(Stanford 1992) (Paull 2009) Infants dependent on mother, and maybe allomothers Bipedality
(limited pelvic width for efficient locomotion) encephalization
(large infant brain size) Pelvic Constraints (Alvarez 2000) Human are altricial in that neonates are:
Slowly maturing & cannot cling to their mothers (Dunsworth et al. 2012)
Born with brains less than 30% of the adult size (Dunsworth et al. 2012) with the fetal pattern of brain growth continuing for a year after birth (Martin 2007)
Heavy for maternal weight (Smith & Tompkins 1995) It is possible that allocare balanced out the development of altriciality in human evolution (Pavard et al. 2007) and can explain several features of human life histories.
Cooperatively breeding is nearly three times more likely to evolve in taxa that produce altricial versus precocial chicks (Hrdy, Mothers and Others, pg.199)
On average, mothers with help wean their young at an earlier age and conceive again sooner and infants grow faster (pg.102) Wet Nurses for the Wealthy
Efe & Aka - nursed by allomothers during first two days of life
Milk Kinship in Islam Infants dependent on mother, and maybe allomothers maternal metabolism "Secondarily altricial" infants Metabolic constraints Obstetrical Dilemma Hypothesis (Wittman & Wall 2007) Metabolic Hypothesis (Dunsworth et al. 2012) Babysitting is the caretaking of infants by an allomother, allowing the mother to leave the infant for a period of time (Riedman 1982)
It is also benefitial for the allomother by allowering her to gain valuable eperiences from caring for someone' else's young for when she has infants herself (Hrdy, Mothers and Others pg.180) (These lions are brothers. They are adorable.) No other immatures depend on others to provision them for years the way that human children do (Hrdy Mothers and Others pg.80)
In the image- Hazda grandmothers help forage May occur in lions by old cubless females (Riedman 1982) Found in 20 Primate Species
Snub Nosed Monkeys
Bolivian Squirrel Monkeys
Red Howler Monkeys
87% Human Foraging Societies
at least occasionally Callitrichids
Bolivian Squirrel Monkeys
Marmosets & Tamarins* The term homosexuality refers to a preference for same-sex partners.
Homosexual behavior, genital contact or manipulation by conspecifics of the same sex, is widespread among anthropoid primates but absent among prosimians (Vasey 1995). If homosexuals increase the reproductive success of kin by providing alloparental care, then the genetic material held in common with kin may offset the homosexual’s lack of offspring.
Since homosexuals would be aiding kin at the expense of themselves, lineages with homosexuals would theoretically have greater survival (Kirkpatrick 2000).
While this is consistent with the kin selection hypothesis, little data exists to test the idea and the role of homosexuality in human evolution remains theoretical. *Less time foraging when carrying,
males: less time copulating (Tardif et al 2002) Popular interest in bird homosexuality shown in 2004 with the “gay” penguin couple of Roy and Silo at the New York City Central Park Zoo (La Fountain-Stokes 2007)
Long term female pairs in >30% of Laysan albatross birds (Zuk & Bailey 2008)
Male-male and female-female same-sex bonds display the same behavioral characteristics as male-female ones (Elie et al. 2011)
They are intense, highly selective, and stable affinitive relationships
Same-sex male bonds were sufficiently strong not to split up when individuals were given the opportunity to reproduce with females. parental manipulation and behavioral plasticity group selection kin selection "fertile female"
x-linked balanced polymorphism
recessive trait In roughly half the 300-odd species of living primates, mothers alone care for their infants.
But only among marmosets and tamarins we find shared infant care combined with extensive alloparental provisioning, such as we also see in humans.
In no primate species are infants dependent for as long and as much as humans. Protection from Predators and Conspecifics Precocial means active at birth
In birds (like ducks)- hatched with eyes open, covered with down, and leave the nest within two days
Altricial means helpless at birth
In birds (like songbirds)- hatched with eyes closed, with little or no down, incapable of departing from the nest, and fed by the parents Human newborns are born with hair, open eyes and are able to cry- but they cannot walk until they are 9-18 months old! Florida scub jays are vulnerable to predation and alloparents help guard the nests (Hrdy, Mothers and Others pg.177).
Allomothers in the fish species neolamprologus pulcher, a type of cichlid, help keep predators away from eggs by acting as a guard because then they may get good territory of their own one day (pg.192). In some peoples of the Amazon basin, fathers (considered allomothers by Hrdy) protect their infants from high rates of intergroup violence. Primate parents do less provisioning when helpers are available.
Avian helpers often provide more food than the chicks' own parents. (Hrdy Mothers and Others pg.181)
In only 20% of primate species do alloparents provision as well as care. (pg.92)
In addition to allomaternal nursing mentioned earlier, cebus monkeys allow some else's infant to take food.
Food offering is less frequent. As many as 1/5 of all instances of food sharing in capuchin monkeys involve food actively offered by an older monkey to an immature. Olive Baboons exhibit male care, which can include protection, when they are likely related to the infant. Marjut Kosonen (1996) studied the emotional support and help that siblings provide and found that when they needed help, children would first seek out their mothers, but then turn to older siblings for support, even before they would go to their fathers.
-from US Department of Health and Human Services pamphlet about foster care
What do you think? Discussion Siblings in Foster Care Allomothering in red howler monkeys typically consists of infant-carrying by adolescent females who are usually siblings of the infant (Pope 2000). When marmosets and tamarins experience high dispersal costs and saturated habitats, older siblings will remain in their natal group to care for younger siblings (Mitani & Watts 1997). Among the Kikuyu of Kenya the mother might work in the garden part of the day, leaving her infant with a girl or young woman (often an older sibling of the infant), in the home village compound (Leiderman and Leiderman 1977). In Washington D.C., 82% of infant transport cases are by parents (mothers and fathers) (Denham 1974).
Among the Alyawara in Australia who abandoned their hunter-gatherer lifestyle 4 or 5 decades ago, 52% of infant transport cases were by mothers and the other 48% were by older sisters or the mother's sisters (usually younger) who did not have infants of their own (Denham 1974). It is extremely hard to find human statistics for babysitting because it is undocumented and sometimes without pay. We take for granted that in modern industrial society we rely on babysitters and they are everywhere! Male couple Pedro and Buddy at the Toronto Zoo Examples in Birds Menopause is unique to humans The Grandmother Hypothesis Human grandmothers are effective at provisioning food Alloparents make substantial contributions in carrying infants (Alvarez 2000). Other species show reproductive declines, but not menopause Grandmothering is very unique Increase in pelvic size for infant brain is limited "Secondarily altricial" infants Altricial young are very dependent on their mothers (and possible others) for a long time- but human are a conundrum- mothers have short interbirth intervals and reproduce later while infants need provisioning for most of their lives! We know human allocare is unique, but what about it?
Next, we will discuss sibling care, grandmothering and care from homosexual relatives (or group members) as unique human adaptations. Sibling care in non-human primates Sibling care in humans Parents whose firstborn was a daughter produced more surviving children then parents whose firstborn was a son- which is presumably because daughters more actively care for younger siblings (Hrdy, Mothers and Others, pg.105)
The more older siblings a child has, the better a child does on tests that require her to see the world the way someone else does (pg.136) Example of sibling care in humans Hadza Foraging & Grandmothering MOTHERS GRANDMOTHERS YOUNG JUVENILES MOTHERS Returns Through Foraging for Resources Requiring Strength and/or Skill Human life histories evolved within a social organization and ecological context in which mothers gather and share resources that juveniles cannot access
Returns of senior women benefit pregnant and lactating kin and their dependent offspring
Postcycling females earn same returns as other unemcumbered females
Therefore, no selection pressure against fertility decline at later ages DISCUSS! Sarah Hrdy also offers another explanation for why humans are special.... Detrimental Grandmothers? When needing emotional support and help, children turn to mothers, then siblings, then fathers
In foster care, older sibling is often only perceived source of help
Secure attachment to an older sibling diminishes impact of parental mental illness or loss
Study of 90 children ages 8-12:
foster children have smaller networks of relationships with important persons
siblings proportionally more important
Having contact with siblings when in foster care yields greater sense of safety, well being, stability, belonging
Continuity of sibling relationships assists in:
maintaining a positive sense of identity
knowledge of their cultural, personal, and family histories
Social skills, especially conflict management, is learned by interacting with siblings
Warmth in sibling relationships yields:
fewer behavioral problems
higher self worth Altricial species with dependent young More likely to have allocare for the dependent young More sophisticated theory of mind and other regarding tendencies to enhance information transfer highly social bring back food to central location unpedictable climate and resources Spark (cc) image by nuonsolarteam on Flickr mother trusts others Take a highly intelligent bipedal primate with the cognitive and manipulative potentials, rudimentary empathy and theory of mind found in all great apes Then rear that ape in a novel developmental context where maternal care is contingent and the infant depends on care and provisioning from caretakers Subject this novel phenotype to novel selection pressures such that infants best at mind-reading are best cared for and best fed Directional selection favoring just the traits (enhanced mutual tolerance, social learning, social communication, perspective taking) that comparisons between humans and other apes require us to explain What do you get? The Mothers and Others Hypothesis Thoughts? Alloparenting? So.....
Why does homosexuality exist? DISCUSS! (We will be sharing some theories too!) or Benefits to the Mother Family Size, Day-Care Attendance, and Breastfeeding in Relation to the Incidence of Childhood Asthma A hypothesis has been suggested stating that children exposed early to infections are less likely to develop atopy or asthma. The authors investigated the relation between risk of childhood asthma and number of siblings as well as day-care attendance, as factors possibly increasing the likelihood of early infections, and breastfeeding as a factor reducing them. A case-control study was carried out in Montréal, Canada, between 1988 and 1995 that included 457 children diagnosed with asthma at 3–4 years of age and 457 healthy controls. Cases followed for 6 years were later classified as persistent or transient by the symptoms and use of medication after diagnosis. Among cases diagnosed at 3–4 years of age, the adjusted odds ratio for asthma was 0.54 (95% confidence interval (CI): 0.36, 0.80) for one sibling and 0.49 (95% CI: 0.30, 0.81) for two or more. The adjusted odds ratio for day-care attendance before 1 year of age was 0.59 (95% CI: 0.40, 0.87). Results were similar with persistent cases. Among transient cases (who possibly had an infection with wheezing at 3–4 years of age), daycare attendance and a short duration of breastfeeding resulted in increased risk. The results support the hypothesis that opportunity for early infections reduces the risk of asthma. Am J Epidemiol 2001;153:653–8.