Sexual Imprinting Flashcards
What defines social bonds?
- Ability to recognize specific individuals
- Recognition is associated with positive emotional effect that stimulates proximity seeking, physical interactions that reinforce positive effect, and imitation
- Physical separation of the individuals causes negative emotional effect and searching behavior
- Aggression towards intruders that threaten the exclusivity of the bond
- Has to be some element of reciprocity
- Relationships between individuals are long term
- Reduced stress response to environmental or social stressors.
Describe the sheep and goat cross-fostering experiments that show sexual imprinting?
• Depend upon the fact that sheep and goats are closely related.
• When goat kids are reared with a mother sheep, or lambs are raised with a nanny goat:
− Play and grooming behavior resembles that of the foster mother, not their genetic species
− Aggression, climbing, feeding and vocalization unaffected and resembles genetic origin
Male Cross-Fostered Sheep/Goats
• Male goat reared by a female sheep → after 1 year, the goats prefer to mate with sheep
• Male sheep reared by a female goat → after 1 year, the sheep prefers to mate with goats
• At this stage, mating preference is determined by the rearing environment
• If you carry on and look at mating preference after 2, 3 and 4 years → it is the same each yaer
→ Mating choice is determined during a window of early developing, and determined by rearing.
Female Cross-Fostered Sheep/Goats
• Female goat reared by a male sheep → after 1 year, there is a 50/50 split between preference to mate with male goats or male sheep
• Female sheep reared by a male goat → aftet 1 year, there is a 50/50 split between preference to make with male sheep or goats
• After 2 years, reversal is evident:
− Female goat reared with male sheep → all the female goats prefer to be mated by goats
− Female sheep reared with male goat → still a 50/50 split
• After 3 years, reversal is complete:
− Both the female goats and sheep prefer to be mated by their own species
→ Rearing does have an impact on their behavior
→ Is reversed after around the year
- This is the phenomenon of sexual imprinting
- Males imprint strongly on their maternal species, females less so
How do sheep and goats recognise the appropriate species to mate with?
How do they recognize the appropriate species to mate with?
Kendrick et al, 2001
• Sheep don’t forget a face
• Sheep were trained to discrimintate face pairs, and then re-tested up to 2 years later
• The right temporal and medial frontal cortex cells respond more strongly to a familiar face
• This region of the brain is also implicated in humans with facial recognition
If you go back to the cross-fostering experiments and look at facial recognition as opposed to mate choice:
- Male goat spends more time looking at a picture of a female sheep if reared by a sheep, and more time looking at a goat if reared by a goat → males imprint strongly.
- Female goat spends more time looking at a goat even if reared by a sheep, and vice versa → females prefer to look at their own species.
→ Males imprint on their mothers face more strongly than females (The Oedipus complex in sheep and goats).
Describe the theory of sexual imprinting in humans
- Suggested that women born to older fathers more strongly attracted to older men
- Adopted women tend to select husbands who look like their adopted father (Bereckzei et al)
Hamilton and MacGowan, 1929
• Commonly thought that men attracted to women that look like their mothers
• Doesn’t seem to be true – more men said wives did not look like their mothers
• However, correlate this with those who are happy – seems those who’s wives did not look like their mothers were unhappy!!
Bereckzei et al,
• Research shown human sex partners resemble each other in many traits
• Positive correlations found between socio-economic status, age, intellect, interests
• One possible explanation is genetic-similarity theory – an extension of kin-selection theory. If organism can identify genetic similarities in strangers, they may exhibit altruism towards them.
• This altruism may take the form of homogamy (inbreeding) which increases the degree to which parents share genes with offspring, thereby enhancing genetic representation in future generations.
• Extreme homogamy has serious reproductive costs → been proposed that a compromise has evolved with individuals with a moderate degree of homogamy.
• Homogamy between non-relatives has been found to enhance marital stability and fertility, and lower the rate of miscarriage in humans.
How is homogamy achieved?
1. Phenotypic matching to self → can occur only if there is high correlation between genetic similarity and phenotypic similarity on traits that individuals use to distinguish potential mates
• Various animals can recognize genetic similarity on the basis of shared olfactory and visual cues
2. Imprinting like mechanisms → similarity between spouses would arise if individuals acquired mate-choice criteria through exposure to their parents. An early fixation to a set of family characteristics would shape mater preferences during adulthood.
− Children may internalize their opposite-sex parents phenotype as a template, and at sexual maturity, prefer those who resemble this mental model.
− In a study comparing more than 300 photos of family members, subjects correctly matched wives to their husbands mother
− Higher degree of similarity seen between husbands mother and wife than the husband to wife
➢ This may initially suggest sexual imprinting is the mechanism rather then phenotypic matching to self, however..
➢ This could be an artifact because of the 50% overlap between parent and offspring genetic material.
➢ Results could therefore been a result of innate similarity detection between spouses, not sexual imprinting on the mother.
To disentangle these effects, study aimed at investigating the mate choices of woman from adoptive families → if sexual imprinting is the mechanism, female would choose a mate resembling her adoptive father, rather than herself (or biological father).
Results:
• Significant resemblance between husbands and wives → seems to be phenotypic ‘genetic similarity’
➢ This is the opposite to goats and sheep, they don’t pick the ones that resemble themselves
• Higher degree of similarity between the husband and the wifes adoptive father → suggests sexual imprinting
• The more emotional warmth the father provided for his daughter, the more similarity was perceived between him and her husband → suggests strong sexual imprinting, supports the notion of recognition being associated with positive emotional effect that stimulates proximity seeking.
➢ This is the same to what is seen in sheeps and goats.
What is meant by the brain chemistry of bonding?
- Oxytocin and Vasopressin closely related
- Some of the most ancient hormones we know
Act as hormones secreted from the posterior pituitary
• Oxytocin → labour, uterine contractions, milk
• Vasopressin → water balance
Also act as neurotransmitters in the brain, acting on the paraventricular nucleus
• Oxytocin → mate and offspring recognition.
Birth and Oxytocin
• Birth and suckling increase oxytocin release
• During birth, the spinal cord reflex arc from the cervix feeds back to induce oxytocin release → oxytocin then acts on the musculature of the cervix (uterotone)
• Vagino-cervical stimulation can mimic the effects of birth and stimulate maternal behavior and selecting bonding → oxytocin induces the same response
• You can do this to make a sheep more likely to accept a foster lamb → stimulate the maternal behavior.
• Oxytocin antagonists reduce maternal behavior and selective bonding.
• Swain et al, 2008 → shown that women who do not have an oxytocin induced vaginal delivery (ie, have a cesarean) have a poorer response to their own babies cry.
