Evolution of Human Sexual Behavior - Midterm I

Females are the limiting sex because they produce eggs, which are much more costly to produce than sperm.
Female obligatory investment is far greater than male obligatory investment because of the difference in sperm (smaller, requires less energy, higher in numbers) and eggs (larger, single egg, requires more energy). Females can have only a limited number of offspring, while males can virtually have an unlimited number. Thus females need to be much choosier, and therefore create sexual selection in males.

In order to gain access to females they must compete for access to resources that will increase their mate value. Therefore sexual selection has acted heavily on certain male traits so that they may compete with other males for females (***intrasexual selection) AND be able to attract females (***intersexual selection).

V-shaped body (more upper body muscle, than lower body muscle)
Masculine face
Penal ridge

A V-shaped body would give a man more upper body strength for combat, in order to compete for women and resources.
A masculine face is an indicator of good genes. Facial masculinity is affected by androgen production during development, which may be a costly signal of food condition.
The penal ridge displaces residual semen of previous male to allow for more successful insemination by current male and exclusion of any other sperm from fertilizing the ovum of the female.

It is possible to be too tall. Natural selection tends to favor the population mean, weeding out the tails of the distribution. Ecological constraints probably caused natural selection to penalize very tall men (eg. Broken bones, higher metabolic costs, poorer balance and agility, awkward gait, and body carriage), causing optimal male height to converge on some constrained limit. (from reading about what women look for in men) --Natural selection and sexual selection can work against each other.

1. Protruding Breasts: Honest signal of residual reproductive value, age. Breast form changes after breast feeding.
2. Facial Neotony: Facial attractiveness such as large eyes, small ears and full lips provide honest cues to health and mate value. There is intrasexual pressure on females to look younger on their faces to enhance prospective reproduction- changing female morphology.

Males are more likely to be involved in violence because they are competing for resources and/or mating opportunity (which will increase their reproductive success). For males, access to mates is the limiting factor for reproductive success. Thus, they will be more willing to take higher risks to obtain mates, even if they will be killed in the process because the payoff in the end (passing one’s genes to the next generation) outweighs the cost of even death. Even after death, males can profit from females taking the burden of internal gestation, placentation and lactation. It wouldn’t make sense for the female to be more violent in their mating effort because it risks the end of an already limited reproductive career--women can only bear so many offspring compared to the many progeny that a male can potentially produce with his relatively cheaper sperm.

If homicide was influenced by different size and strength of males and females then it would only make a difference if those who were less in size and strength (women) were victims of those who were greater in size and strength (men). But, as research indicates, this is not the case. Men rarely commit homicide against women. In comparison to the amount that men commit homicide against other men, women victims are proportionally smaller.

Risk-taking behavior-- Taking more risks gives you higher status, a reputation follows you. Ultimately selection may favor increasingly dangerous behavior, because it distinguishes fitness levels among males. The “winners” are potentially those who have a higher mate value/quality and will ultimately gain access to females and therefore increase their reproductive success. This is a time in their lives of: uncertainty in their future success, sexual maturity, peak physiology for power activities (more fast twitch muscles, upper body larger than lower body). These dangerous behaviors are a way for men to compete indirectly or directly with each other to gain reputations, achieve status, acquire resources etc.

females should be attentive to risk taking behavior because it is an honest signal that the male has survival skills. § Risk taking selected for as a mating strategy (honest signal that peacocks can survive predators). Will be impressive but will increase probability of mortality. The males who survive risk taking behavior will potentially be of higher fitness than males who do not survive risk taking behavior.

ii) -Direct contest (win it now).
Reputation effect

This directly relates to the fact that selection pressures have been stronger in males than in females. Females are more selective in their choice of a mate which is why males must compete in risky behaviors in the first place: to get females’ attention and advertise themselves as quality mates. Therefore if a male can show off his mate value, through honest signals of risk taking in front of multiple women, his access to the number of females may be potentially increased. It’s worth it to overcompensate.

When the availability of resources is unevenly distributed between males, we can expect males with more resources to have access to more females, therefore higher levels of reproductive fitness. Males with lower resource availability therefore must find a way in which they can compete with more successful males. This usually results some risk-taking behavior. Thus males with lower resources have less to lose in risk-engaging behaviors. Therefore, in societies were we see a greater inequality in the distribution of resources, will have higher statistics of risk taking behaviors like homicide.

1)low sexiness ranking: if a female is not highly attracted to her partner, during times of high fertility, she may exhibit higher attraction to males who are attractive.
2) lower social status: though he may be willing to provide for her, if he is lower on the social scale, he may not have the means to protect her, no “insurance” – this can be increased with an EPC with a higher status male

1) More masculine features: facial masculinity is affected by androgen production during development, which may serve as a costly signal of good condition. Studies have shown that women have a stronger preference for men with more masculine facial features as potential short-term mates, especially around the fertile phases of their cycle (ovulation). Male attractiveness may serve as an honest signal of good genes.

i) Older = more access to resources, more time to have built up a reputation/status.
ii) Females may be less sexually attracted to the older men. Since they are constantly looking for good genes for their offspring, they may be more susceptible to EPCs with younger men that exhibit better, healthier, younger genes.