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why did Darwin have trouble explaining secondary sexual characteristics with NS?
- Secondary sexual characteristics had no survival advantage. animals can survive with out them. Natural selection favors survival, sexual selection might not.
- ex. peacock tails decrease survival, but increase RS
what are the two types of Sexual Selection? how do they differ?
- Intrasexual selection:
- -competition over mates.
- -selection for traits that enhance an individuals ability to compete (usually male-male competition).
- -may lead to sexual dimorphism between genders.
- 4 specific subsections to intrasexual competition:
- -contest competition: selection for traits that will enhance competition, promotes sexual dimorphism.
- -scramble competition: race to copulate with as many females as possible
- -sexual coercion: herding, forced mating, infanticide.
- -sexual persuassion: grooming, feeding, protection
- Intersexual selection:
- -mate choice (female)
- -selection for traits that enhance individuals ability to attract opposite sex
- -resembles sexual selection
variance among males is larger than variance among females in terms of RS. what does this mean?
- -males can produce more offspring than can females potentially. mean: # of offspring is equal for males and females.
- -the variance of RS within a sex is a measure of selection intensity (?).
- -the greater the variance, the greater the strength of selection.
- -so, if there is a high variance in male RS and only a few males mate. there will be strong selective pressure on male competitive ability.
what is Bateman's principle?
females tend to limit male RS MORE than males limit female RS.
what limits male RS?
- fertile females, because they pay the majority of reproductive costs through gestation and lactation.
- male RS also highly depends on the availability of fertile females.
what types of males and females are the result of the classical model of SS
Males quantity-seeking with more mating effort; Females quality-seeking with more parenting effort. The stereotypical male/female roles. Men are supposed to be promiscuous, cheating, varmints whereas females are supposed to be timid and reserved.
Sexual dimorphism is greatest in which type of group?
single-male groups because the males would have to compete against each other to see which would be the leader of that group, and the dominant male would lead the group, and all the other males would have to go find another group
In polygamous groups, a single male can potentially breed with more females than under monogamy; selection in favors of adaptations that enable males to gain access to females is proportionally stronger. Species with brightly colored, large or dangerously armed males are more often polygynous. (Sexual Dimorphism: the differences in appearance between male and female of the same species, as in color, shape, size, and structure caused by the inheritance of sexual pattern in genetic material. (Think of the peacocks and peahens).
sperm competition leads to what type of traits?
- Scramble- sperm production, and quality of sperm. more sperm competition = more promiscuity.
- Larger genitals to allow for ejaculation at a moment's notice.
Sexual coercion of females by males is expressed by which traits?
herding, forced mating, infanticide- in primates
females choose males based on indirect and direct benefits. define the two and give examples of each.
- Indirect Benefits:
- -good genes, healthy offspring (looks).
- Direct Benefits:
- -resources (good provider), parental care, male status, personal benefits (money) (availability).
what are the direct and indirect benefits of choosiness
- -traits as honest signals
- -costliness of trait ensures its honesty
- -some traits signaled with a handicap
- -costly signals stay honest
- -can not be faked
- MHC and strong immune system, parasite resistance
is dispersal costly? explain
- -energy to move yourself around, and, for most humans, your items.
- -leaving familiar location.
- -could get lost.
- -knowledge of local resources, hazards, people.
what is the simple biological rule we employ to avoid mating with kin?
- -avoid those familiar from youth, do not mate with those you grew up with.
- -MHC- people with similar immune systems do not smell as good, which makes them less attractive.
why do female gorillas leave the group at sexual maturity?
- -one male/multiple female group
- -fathers are generally in control
- -inbreeding avoidance
what is the difference between exogamy and endogamy?
Exogamy: preferred marriage partners come from outside community or group.
Endogamy: preferred marriage partners come from within community or group.
what is the most common residence pattern?
Patrilocal: couple lives in husbands natal area (72% of the population according ro Murdock).
the Yanomamo experience constant warfare. what is their residence rule and why?
- -related males cooperate
- -rule is to keep sons at home, and use daughters to form alliances with other groups (patrilocal).
where are all humans from?
- East Africa
- -Great Rift Valley on the Omo river in Ethiopia, western side.
why do we study people like the !Kung? what can we learn from them?
The !Kung represent the original humans. Studying them is studying past humans. We can learn what our early ancestors were probably like.
what are the reasons why it is so remarkable that we are still alive and that we ever left Africa?
The territory of Africa makes it incredible that we ever left africa to extend to the other continents.
- survival rate could have been really low, so it is remarkable that people survived and repopulated
intercourse early in the ovulatory cycle is more likely to lead to a...
Girl, a male is more likely around the middle the of the cycle,when vaginal conditions are juuuuuust right. X chromosomes last longer but swim slower; Y chromosomes swim faster but die quicker.
what is the sex ratio at birth expected to be based on out sex chromosomes?
from lecture and the book, how do we know hat female coypus can recognize the sex of their fetus?
From dissection of coypus, it was found that coypus would abort their young at a certain time, so the dissected uteruses of females past a certain point in their pregnancy carried only males. (pg 330 )
what determines parental investment in offspring- or why deviate from 50/50 sex ratio?
- -variable RS
- -this varies by good/bad conditions of the mother and the environment
- -maternal condition/male status
- -for humans, culture
explain the Trivers-Willard Hypothesis
- Interaction between maternal condition and the impact of investment on RS
- Better maternal condition should mean more males (want for high-quality males). Because male RS is so variable, a mother will want to produce a son in conditions that will yield more successful offspring so that their son is a
- better competitor. Also because males are more expensive to raise and will require more resources. If the mother is in poor condition, she should have females.
India, for centuries has practiced sex biased infanticide. T/F? support your answer.
True, males are favored because females cannot inherit property and must pay a dowry to have married off.
from the Portugese example, mothers have fewer (xx/xy) during poor harvest and more (xx/xy) during good harvests? does this support TW prediction?
Fewer boys (XY) in poor harvest, more boys (XY) in good harvest. Supports TW predictions.
why is the relationship between education and income a viscious cycle among women?
- Educating a child is costly while an uneducated child will be
- able to do work. Women who continue to educate their children will have a lower income, because the women would have to pay for their children’s education while women who choose to have their children work will have uneducated offspring.
describe the four types of mating systems
Monogamy: limited mating opportunities, male investment in offspring is high, male confidence in paternity is high, little sexual dimorphism, territoriality
Why: Ecology and parental care
Polygyny: clumped resources, females congregate, high variance in male RS, female receptive one at a time
Why: possible for one male to defend access to multiple females
Promiscuity: multiple males and females, females mate multiple, in chimps multiple males must defend a territory, males with highest fitness can mate multiply and often leads to scramble competition
o Why: females benefit from mating multiply, males do not succeed in monopolizing access
Polyandry: When one female has multiple males. Rare in mammals in general but occurs in tamarins and marmosets, occurs in humans as well (poor conditions where multiple male investment is crucial), Generally the males are related. Example of humans is in the Himalayas.
Polyandry is a very common mating system T/F?
False. this is only common in the Tibetan plateau (from the movie)
what does the polygyny threshold model predict?
Choice of husband based on amount of resources per wife. A male with high resources will be able to satisfy the needs of multiple females whereas a male with low resources can only support a few if any.
what are some of the consequences of polygyny in terms of sexual dimporphism?
- Greater sexual dimorphism because of greater variance in reproductive success.
- -some men horde all the mating prospects while others are left with nothing. this increases competition, and means that males have to be bigger, stronger, etc. to be competitive. females, because they don’t engage in direct competition (their r.s. is determined by access to resources, not access to mates) have no need for the adaptations that men have.
What is the sex role reversal? Give an example.
- one sex fulfills the stereotypical roles of the other sex.
- Ex. Jicanas- males take care of offspring.
rich people in rich countries are having more kids than poor people in rich countires as expected by evolutionary theory. T/F?
False, the opposite is true. Rich families tend to educate offspring and due to the high cost of higher learning, they can only afford to raise a few children. Poor families have more children that can work.
how does contraception decrease child mortality?
low birth causes a low death rate. it increases birth spacing. so mother will have to care for fewer offspring at any one time.
why is educating children more of a benefit in developed countries?
- education decreases number of deaths and births. it is more a benefit in developed countries as opposed to underdeveloped.
- by developed countries becuase in developed countries, education increases economic/job opportunities and access to resources, while education in underdeveloped countries may not be necessary for most jobs, and therefore unhelpful economically.
why are children not as useful in the west?
labor laws enforced during the 1930's stopped children from going to work.
the majority of the world is found in which societies? which societies consume the most resources? why is this result striking/interesting
most of the world’s population is found in “developing” countries, yet “developed” countries use many more resources. even though developed countries generally have more population growth, per capita, people in developed countries use more b/c they can afford to use more (resources).
what are the two functional explanations for why we see clitoridectomy?
Makes sex less enjoyable for women thus lowers female sex drive. Intended to keep women from cheating on their male partner and from keeping the males themselves from cheating on their female mate. Also, creates paternity certainty, giving the child more father investment.
in all societies, mothers care more than fathers. T/F?
unmarried, young mothers have the lowest rates of infanticide. T/F?
False, they have fewer resources and cannot care for their babes, therefore, Infanticide
mothers care only because they can. use examples to support your argument.
- For argument: Yes, only women can lactate. Mothers are certain it’s their child, so they can care for it.
- Against argument: titi monkeys for example, males invest in their infants more than the females.
- You could also say that they care more because they are certain that that offspring is theirs.
when paternity certainty is high males invest in their ______ children. when it is low they invest in their______ children.
own/sisters. This is true, males won’t care for a child that could be another male’s offspring but they will care for their sisters child since it will carry about 25% of his genes.
fathers increase their parental care as they take more wives. T/F?
from lecture, why do we see the gender based division of labor? why do males hunt, mine, and cut timber while women gather, carry firewood, and cook?
Men do the jobs that women are unable to do because they are dangerous and too difficult to perform while also holding/caring for a child. Women also do jobs that contribute more to their offspring/family for better RS, while men do not necessarily need to contribute directly to their family for high RS (e.g. sharing food with others outside family for more mates).
females gather primarily to for their family. support.
When females bring back the resources they have gathered, it is rarely shared with others outside of the family, meaning that it goes directly to the family. While males share, gaining alliances as well as increasing their RS (the more meat brought home, the more copulations).
what are some other benefits to being a better hunter?
greater RS. more resources can potentially lead to more mates.
how could sex biased infanticide actually create positive social change?
Lack of females would give more respect to females. -Chase
Possibly: lower population growth, creating more resources.
describe the two functional hypotheses for why we see ageing in humans.
the faust hypothesis
- the two functional hypotheses for why we see ageing in
- humans is the faust hypothesis and truck hypothesis
states that you gain benefits early on but pay for them later in life (early benefit, later cost - live now,pay later)
the truck hypothesis
states that you can only choose to invest in one thing at a time - either reproduction or repair. you can invest in reproduction and mating (taking your truck for a drive), or you can invest in repair and maintenance (cleaning your truck at home), not both, and because we can't do both - we age
greater investment in reproduction increases the age at menopause. T/F?
False, if you invest in reproduction your body is automatically not investing in repair. Without repair, your body will go through menopause and die faster.
human life expectancy increased greatly with the introduction of agriculture. T/F
True, agriculture made things a lot easier than gathering. Allowed for more stability and greater life expectancy.
describe the mother and grandmother hypothesis for the evolution of menopause.
Adaptive for women to live long after they could no longer reproduce so they could continue to increase RS by taking care of their grandchildren. Grandma can provide resources for her grandchildren. From the reading, the ‘grandmother hypothesis’ is when “a grandmother has a decidedly beneficial effect on the reproductive success of her children and the survival of her grandchildren.” Can offer general child care, as well as food resources.
what are other explanations for menopause?
to prevent birth defects and less adaptive children to be able to care for the last child before death and without reproducing more children that will not be taken care of fully cause the mother dies too soon in its lifetime Also, to prevent death from attempting to give birth at an old age.
developing countries have unequal access to many things that lead to higher levels of disease. describe these.
- Clean water, medicine and medical attention, sufficient
- food and nutrients, protection and shelter
American’s have health care, so few are dying from disease, and more are dying from old age. Developing countries do not have health care, so many die of disease before they are old enough to die of old age.