Parenting in Emperor Penguins (Antarctica)
Adaptive challenges of a very harsh climate.
Pair bonding facilitates biparental care.
K-selection ?
few offspring, high parental care investment in each one (offspring).
- extreme e.g. = kangaroo - have one joey (at a time), put in their pocket.
R-selection
many offspring, but low PI; quantity is often offset by high predation.
- extreme e.g. = frogs - lay an extremely large number of eggs. - still a lot of diversity in frogs - swallow their offspring to protect them.
Parental care is costly to parents (opportunity costs of mating, feeding selves, etc.)
- For months after birth, they cannot do anything for themselves at all. why are humans are essentially born premature?
- Width of pelvic cavity = compromise between neonatal head size and requirements of bipedalism (Gruss & Schmitt, 2015).
- Pelvic cavity is engaged in a tradeoff with the timing of the birth of the infant. - If the baby stayed in the womb longer, its head would be larger and could start to interfere with locomotion and other physiological processes.
Why are men’s PI usually less than womens?
Female PI was more essential for offspring survival in the past. - e.g. gestation, lactation, ability to emotionally interact with the child.
Women’s adaptations for parental care?
- Compared to men, women display superior theory of infant mind.
- Better at recognising infant facial expressions, especially negative emotions (Hampson et al., 2006).
- Compared to nulliparous women, new mothers display greater activation in ToM regions (Zhang et al., 2020).
- In new mothers, higher activation in brain regions involved in (a) facial expression processing, and (b) empathy and mentalising.
‘Tend and befriend’ (Taylor et al., 2000) to deal with stressful situations - alternative stress reaction to flight or fight. - if children are around, they will focus on protecting and calming the children.
- establish a social network.
Why does mens PI tend to be less than womens?
- Mating opportunity cost - as sexual selection and PI theory predicts, this should be higher for males (because they have more to gain from multiple mating as they can reproduce faster)
Why is mens PI generally lower?
- When male to female sex ratio is higher
- Among more attractive males
- When the population density is high (in birds as well as humans)
- Paternity uncertainty is another reason -
The EEA for parenting adaptations, females always had 100% certainty of parentage, men never did
Paternity certainty and facial resemblance.
- Emotional closeness reported by fathers, but not mothers, predicted by facial resemblance to self
- Facial resemblance to self predicted higher PI in fathers but not mothers
Regardless of resemblance, relatives are much more likely to say the baby resembles the father more than the mother, especially when the father is present, especially with the mothers family (Daly & Wilson, 1982). - strategy of encouraging PI from father.
Effort to promote paternity certainty.
adaptations for parental care should be sensitive to three areas
Genetic relatedness: Are children really my own?
Can offspring convert parental care into fitness? - how likely is the infant to survive?
Could investment be better spent in some alternative way? - kin altruism?
Cross-culturally, men invest more when -
- In their own genetic children than step children
When they are more sure of partner fidelity (Apicella and Marlowe).
When the child’s mother is a current mate (Gray and Anderson, 2010).
Parental care is a form of mating effort.
most important risk factor for child abuse/murder?
step-parenthood.
Abuse of unrelated children
Not an adaptation to abuse/kill children.
But some species do have this adaptation.
Infanticide by males in lions and monkeys.
Congenitally abnormal children are on average
At higher risk of abuse (daly and wilson, 1981).
Recipients of less parental care, because they’re more often )
institutionalised (Census Bureau, 1978).
Recipients of less positive attention from mothers (Mann, 1992).
On the other hand, women with abundant resources actually invest more in higher risk (premature) infants (Beaulieu and Bugental, 2008).
And congenitally abnormal children of course often inspire intense PI
Risk of being killed by genetic parents is the highest for infants, then decreases steadily
I.e, risk correlates negatively with reproductive value - the older you get, the more likely it is that you will survive.
In a sense, they value their children more in terms of their ability to survive.
Not due to the child becoming better able to defend themselves - reverse trend is seen with the risk of being killed by nonrelatives (older kids more likely to be killed).
Parent-offspring conflict Trivers
You’re related to self by 1.0 (100%), but to siblings by 0.5; mum is related to both by 0.5.
You have 2x more interest in your own needs than in siblings’; mum is equally interested in both.
General prediction: children want more parental resources than parents want to give.
- Parents encourage kids to value each other more than kids are inclined to.
Parent-offspring conflict Haig:
Infant waking at night to suckle is an adaptation to extend mum’s lactational amenorrhea (delays next birth).
The effect of imprinted genes (silenced by the other parent’s genes), suggest that the infant’s genes of parental origin are selected to favour longer interbirth intervals than the infants genes of maternal origin.
The infant’s paternal genes promote greater wakefulness, whereas its maternal genes suppress it (data from infants within genetic imprinting syndromes).
If the infant is affected more by the paternal genes, it is going to wake at night and cry, basically demanding more investment from the mother.
Conflict between the mothers genes and fathers genes.
Because the father wants maximum investment from the mother because this is his offspring.
Whereas the mother, the investment she’s making could more likely interfere with her ability to invest in other children that might not be his in the future.
In utero conflict? Haig
Foetus may produce hCG hormone to prevent its own abortion.
Foetus may cause the mothers arteries to constrict, increase blood flow to the foetus, causing high blood pressure
Hamilton - Fitness should be thought of in terms of replicating genes, rather than reproducing individuals.
A gene can enable its own replication by promoting the reproduction of either -
The individual in whom it’s contained, or,
Individuals who contain exact replicas of it.
The tricky part is how the gene can identify the other individuals in which it is contained.
Individuals don’t display their genotypes like labels, so assessing relatedness can be a challenge.
In general, the likelihood of sharing a gene will be associated with genetic kinship.
What psychological adaptations do humans use to detect their close genetic kin?
Raised in the same household - Westermark effect.
Same investment from parents.
Watching a sibling be breastfed.
Perinatal association to mother.
Hamilton’s rule:
C < BR.
C = cost of altruism to the altruist.
B = benefit of the altruism to the recipient.
R = coefficient of relatedness (probability of that gene being present in the other individual).
R = 0.5 for full siblings, so for altruism to evolve, B must be at last twice C.
R = 0.25 for half siblings, grandparents, grandchildren, aunts, nephews, etc; 0.125 for first cousins.
Hamilton’s rule is very good for explaining close genetic kin, but useless when you get to first cousins.
As kinship distance grows, it is increasingly difficult for altruism to evolve.
Selection for kin altruism is called ‘kin selection’.
Kin altruism relates to the concept of ‘inclusive fitness’ (an extension of Darwin’s ‘classical fitness’).
What is inclusive fitness?
Inclusive fitness - fitness in terms of your kin also.
What is the main kin detection cognitive mechanism?
Westermarck effect.
If you are raised in the same household, you will grow up to be not sexually attracted to them.
Those are cues that over evolutionary time are reliably associated on average with knowing that is your sibling.
Has always worked for our evolutionary ancestors
What specific cues might enable the Westermarck effect (Lieberman et al., 2007)?
Perinatal association with the mother, e.g. breast feeding.
Perinatal altruism. - parents being equally altruistic with this other person who lives with you.
