Week 3: Readings Flashcards
sexual selection favours… and is a form of….
traits that aid competition over mates and is a form of natural selection.
The evidence for the claim that sexual selection is only weak-moderate in humans….
vs.
The evidence for the claim that sexual selection is only strong in humans….
Weak-Moderate:
size
- males have 15-20% more body mass than women
monogamous mating
- found in species with low sexual dimorphism
biparental care
- found in species with low sexual dimorphism
low canine tooth dimorphism
- canine tooth dimorphism is a trait found in species with high male competition (mechanism of sexual selection)
High: weaponry courtship displays intrasexual competition Autonomy
why may sexual selection be underestimated in humans?
misinterpretations
sexual selection can impact the sexes similarly which makes the effects of sexual selection appear smaller than they really are. For example there is evidence that there is significant overlap between male and female psychology as a result of sexual selection BUT it is still stronger in males.
Humans deviate from primates in their ability to create weaponry/fists that replace the function of canine teeth.
Women have 40% more adipose than males to help with nursing which is present in humans and not other species.
Monogamy as evidence of sexual selection must focus on the variance of monogamy in humans and not the outcome. For instance, polyamory exists in 83% of societies and sexual selection is highest where there is more reproductive variance.
sexual selection predominates in the sex with…
but…
less investment in offspring and had greater reproductive variance = males (not as strong as other primates but still strong).
but human women still have higher sexual selection than other non-human female animals.
variation in male reproductive traits causes…
competition between females for the better mate and leads to mate attracting features to be selected for by sexual selection (i.e., big hips, butt, breasts, a youthful face, higher pitch voice, less body hair etc.)
even though human males have lower investment than females they still…
have higher investment into offspring via the provision of resources, protection, and parental care relative to other primates and thereby can not spread their genes (sperm) wide and far.
(5) mechanisms of sexual selection:
contests:
the exclusion of same-sex competitors through force or threat of force.
mate choice:
the high investment mate expresses a preference for traits that indicate reproductive success and fitness which increases the chance of mating/conception.
scramblers:
competition to locate fertile females.
sexual coercion:
use of force or threat against a potential mate, at a cost to him or her, that increases the odds of mating and decreases the risk of them mating with a competitor.
sperm competition:
competition within a single female between the sperm of multiple partners.
All played a role in human evolution but contests competition will be the most important. In males, this manifests as violence, dominance, and aggression but in women, this manifests in mate choice.
mechanisms for sexual selection in men..
similar to apes its contest competition is the important sexual selection mechanism.
violence and aggression (i.e., warfare, IPV, bigger size, muscular, facial hair, deeper voice) are more common in human males than females which act as threat signals to other same-sex competitors rather than attracting a mate.
(i.e., dominance and social status amongst men).
dominance and social status are associated with higher reproductive success in industrialized and non-industrialized socities.
mate choice by females differs in the short or long term. contest traits more important for short term but resources and friendliness are more important for long-term relationships.
small evidence of sperm competition in ancestral men but is less prominent since the introduction of monogamy which facilitates parental investment into offspring and stratified societies.
scramble competition was present in ancestral hunter-gatherers as evident by adolescent males traveling further at the peak age of development for mate searching (not females)
mechanisms for sexual selection in women..
less frequent or extreme physical aggression in women relative to men but when it does occur it is typically over mate competition.
aggression is more common in sexually mature women, based on female-biased local sex ratios (more women than men) and greater resource variance in men increase competition and result in more female aggression.
males bigger size let them influence the outcome of f-f competition.
males than females because they had greater sexual coercion and thus, females’ traits are likely to be the result of this and not mate competition.
(e.g., facial shape, body hair, high pitch voice, breast hips and butt etc.).
sexual selection in human psychological sex differences
behavioral sex differences arise when males and females augment reproduction and mating differently.
the fact that ecology and phenology can produce different solutions to the same adaptive problems makes making specific sex difference predictions harder to do but general claims and directionality can be made.
i.e., women’s higher investment should make them picker over mates, and males with low investment will be in favor of non-committal sex with multiple partners and increased competition over mates.
this hypothesis is supported with cross-cultural evidence that supports its universal finding.
However, there is significant overlap between males and females so it is a question about degree (strength of the relationship) and not kind (present or absent in one sex).
males 2.4 SD’s higher than females.
the most basic evolutionary mate preference is sexual orientation.
Main point
males anatomy and behavior indicate the presence of contest competition and females mate attraction (guided by males variance and not by their own accord/choice).
there are multiple forms of sexual selection
sexual selection varies across species but tends to be higher in males or the lower investment mate.
.
Sexual dimorphism between male and females result from the use of differential mating strategies (contest vs mate choice)
The highest sexual selection occurs in the sex with the highest variance.
Female traits to attract men is a form of intra sexual competition as a result of male variations increasing competition rather
.
Sexual dimorphism between male and females result from the use of differential mating strategies (contest vs mate choice)
The highest sexual selection occurs in the sex with the highest variance.
Female traits to attract men is
