Part Two: Short Answers (8 pts each = 40 pts)



Secular Trend

|The secular trend is a phenomenon where the age at which girls experience puberty and in particular menarche is decreasing. |This trend is likely the result of increased growth, in particular skeletal maturation, as a result of better nutrition. We as a whole are healthier than previous generations. | |

| |This means that there are few visible/olfactory signs |Humans have concealed ovulation unlike some other primates |

|Concealed Ovulation |of ovulation (eg. No estrus swellings). |(e.g. chimps). |

| | |Need to give one of the following explanations for the |

| | |evolution of concealed ovulation in humans |

| | |-One thought is that this continuous receptivity in humans |

| | |has strengthened the pairbond and increased parental |

| | |investment through increased copulations. |

| | |-It strengthened the pairbond because males needed to stick |

| | |around to ensure paternity. --Ovulation is hidden because if |

| | |women knew they were ovulating wouldn’t have sex because of |

| | |painful childbirth. |

| | |-Humans have concealed ovulation because sexual swellings are|

| | |energetically expensive. |

|Bridewealth |Resources passed from husband’s family to bride’s |Men appear to pay a higher brideprice for women with higher |

| |family at marriage in many traditional societies. |reproductive value, that are nulliparous, and those that live|

| | |further away from their mother |

|Menstrual Taboos |Taboos, including negative associations, fears and |Number of hypotheses for taboos have been proposed. |

| |restrictions surrounding menstruation. Need examples |Anti-cuckoldry hypothesis: Beverly Strassman through her work|

| |of menstrual taboos- these could include: sexual |with the Dogon, came up with this hypothesis. She claimed |

| |intercourse prohibited, husband wife sleep apart, |that menstrual taboos, and menstrual huts in particular, |

| |cannot cook for men, food and hygiene restrictions, |reveal a woman’s menstrual status to her mate. Her mate and |

| |cannot attend sacred places or perform/participate in |his family then know that she is neither pregnant nor in |

| |certain rituals including the fast during Ramadan, |amenorrhea and that she will soon be ready to conceive. This |

| |cannot perform certain labors, prohibited from |information is then used by men to protect against cuckoldry.|

| |touching male items because it could contaminate it, | |

| |cannot touch another women’s fire, need to be in |Energy Balance Hypothesis: Professor Knott thinks that |

| |seclusion. |menstrual taboos work to promote the probability of |

| | |conception through decreasing women’s activity levels and |

| | |workloads. Almost all menstrual taboos involve a decrease in |

| | |strenuous tasks and an overall decrease in activity. By |

| | |decreasing energy expenditure, this may have a positive |

| | |effect on the probability of conception and thus may serve |

| | |and adaptive function. |

| | |Functional Hypotheses- menotoxins (bacterial contaminants in |

| | |blood), menstrual odor interferes with hunting. |

| | |Cultural Psychological- castration anxiety, male dominance, |

| | |shows not interested in wife’s fecundity, social control, way|

| | |to induce men to hunt. |

|Foreskin |Foreskin is a fold of skin that covers and protects |Foreskin is removed during male circumcision |

| |the glans penis and is the area where smegma is |-circumcision especially found in patriarchal partrilineal |

| |produced- smegma protects and lubricates the glans |societies |

| |during intercourse. |symbolizes belonging to male kin group |

| | |take place at birth or at puberty |

| | |took place as cure for masturbation |

| | |USA only country with non-religious circumcision |

| | |80% of men worldwide not circ. |

| | |1984-40% of us babies not circumcised. |

| | |Risk of mutilation/damage |

| | |Emotional stress |

| | |Ulcerations |

| | |Decreased sensitivity |

| | |Decreased lubrication |

| | |Increased tightening of skin of shaft |

| | |Possible decrease in rates of penile cancer |

| | |Decrease risk for AIDS and possibly other STDs |

| | |Decreased risk of UTI |

|Fecundity |The capacity to bear offspring |Affected by changing nutritional status and energetic status |

| | |or vague |

| | |Higher levels of estradiol and progesterone are associated |

| | |with increased probability of conception. |

| | |peaks around age 27 |

| | |different from fertility |

|Myhrr |Myrrha who was the daughter of Theias, a legendary |Myhrr is one of the most common ingredients in abortificants |

| |King of Assyria, who was raped by her father and bore |from ancient Greece to the renaissance. |

| |him a son (Adonis). She sought the assistance of | |

| |Aphrodite and the other gods who transformed her into | |

| |a plant called Myrrh. While in tree form she bears a | |

| |son. | |

|Graafian Follicle |The dominant follicle containing a mature ovum. The |The increased production of E by the dominant follicle sends |

| |follicle that grows the fastest and becomes |negative feedback to hypothalamus and pituitary to stop |

| |independent of FSH first is selected as the dominant |producing FSH and LH. Therefore, growth of other follicles |

| |follicle. |that need estrogen to grow are stopped. Some credit given to |

| | |evolutionary accounts of the competition between follicles- |

| | |selection for the best quality follicle… |

|Sexual Dimorphism |The systematic difference in form (usually size) |-Useful as a morphological indicator to tell us about |

| |between individuals of different sex (males and |relationship to social/mating system |

| |females) in the same species |-Monogamous species have low level of sexual dimorphism; |

| | |whereas polygynous species exhibit high sexual dimorphism |

| | |- Humans show low sexual dimorphism (females about 85% size |

| | |of males- most significant in upper body) compared to other |

| | |species , although there is still some degree of dimorphism |

| | |(mostly in differences in upper body), indicating we may be |

| | |more monogamous, although most societies allow polygyny |

| | |- Indicative of degree of male/male competition |

| | | |

| | | |

1. Menarche:

a. Briefly describe the two main hypotheses for the timing of menarche in girls.

A) Frisch “Body Fat” Hypothesis

- Accumulation of weight or fat is critical for menarche

- VERSION 1: Avg weight at menarche is 47 kg; thus 47 kg is a critical weight that triggers menarche PROB: graph shows there is no relationship

- VERSION 2: Looked at weight for height instead; found critical body composition that triggers menarche PROB: assumes difference in body composition is due to FAT

- VERSION 3: Few girls reached menarche below 17% body weight as fat; said this was a minimum threshold for menarche PROB: no evidence of increase in probability of reaching menarche after attain 17% body fat

B) Tanner/Ellison “Pelvic Size” Hypothesis

- A girl must reach an appropriate age of skeletal development in order to reproduced; natural selection has delayed menarche until pelvis can handle reproduction without complications

- Pelvic dimensions are significantly correlated with menstrual age

- A bi-iliac diameter (pelvic breadth) of 24 cm seems to be a minimum threshold

- Ellison studied data from 67 girls weighed and measured 2x/year from 8-18 yrs; found that weight accounts for 18% of the variance in menarcheal age; height accounts for 50% variance; menarche occurs after peak growth spurt

b. Which hypothesis seems most plausible? Cite one piece of evidence that supports that hypothesis.

Pelvic Size: Fat is critical for female reproduction BUT attaining an adequate SIZE comes first (Ellison’s). Also explains more variation in timing.

2. List and explain three forms of sexual selection. Give an example of each kind of selection.

1. Intersexual (between) selection, a form of sexual selection involving choice of mates (one sex choosing to mate with members of the opposite sex). Also called female-choice where females choose males based upon elaborate ornamentation or male behaviors. Ex. Peacock, bower birds, birds of paradise, human examples- eg symmetry.

2. Intra-sexual Competition -within): Form of sexual selection involving competition for mates (competition of members of one sex for members of the opposite sex). Also called male-male competition in which males compete for territory, access to females, or areas on mating grounds where displays take place. Male-male competition can lead to intense battles for access to females where males use elaborate armaments (e.g., horns of many ungulates). Examples: Stick fighting in Surma, antlers-deers, female baboons/mangabeys, sperm competition,

3. Male Sexual Coercion: it is the use of force or threat of force by members of one sex to coerce mating from members of the opposite sex. Examples: orangutans -forced copulation, chimpanzees),

3. Control of Female Sexuality:

a. Describe 3 examples of the control of female sexuality across cultures.

- Infibulation/Clitoredectomy-

- Purdah

-Footbinding

b. From an evolutionary perspective why might males want to control female sexuality?

Paternity Confidence/Certainty- The need for paternity confidence may be the force behind men's drive to control female sexuality. This may be particularly true when men have resources to be passed on.

c. Continuing to use an evolutionary argument, why do women often perpetuate these practices?

Women often perpetuate these practices in order to compete for the highest quality/status males with lots of resources. Since chaste, faithful women are often preferred, women may engage in these activities (or pressure their female family members) as a way to display these qualities to men and find men who are willing to invest in them and their children. Also, female relatives may perpetuate these practices on behalf of male relatives- to help ensure a male relative’s paternity confidence and thus their own inclusive fitness.

4. Menstruation:

a. What is one proximate (non-adaptive) explanation for menstruation?

Energy Economy Hypothesis (Straussman): outer layer of endometrium is too bulky to absorb, more costly to maintain endometrium than to grow a new one; higher metabolic rate during luteal phase-----external bleeding as a side effect when there is too much blood or re-absorption

or

Consequence of Uterine Evolution (Finn)- increased permeability of blood vessels that supply the endometrium; differentiation of endometrial wall occurs during every cycle, blastocyst embeds in wall; menstruation as a consequence of terminal differentiation; necessary consequence of having an invasive blastocyst; change in cells to allow invasiveness and they can’t go back to earlier stage; if no implantation, cells must start anew

or

After ovulation occurs, the granulosa cells and theca cells come to together to form a new gland called the corpus luteum. Under the influence of LH the corpus luteum produces both Progesterone and Estradiol. The P and E produced by the corpus luteum cause the endometrium to thicken so that if fertilization occurred, it could support implantation. If implantation does not occur, Human Chorionic Gonadotropin (hCG) (hormone produced by embryo to signal to the mother “I am here- I need the corpus luteum”) is not present then corpus luteum degenerates. Estradiol and progesterone decline and the endometrium sheds- hence menstruation.

b. Explain and contrast two hypotheses for the evolution of menstruation.

Pathogen Defense Hypothesis (Profet): menstruation evolved to protect the uterus from sperm-borne pathogens

Embryo Elimination Hypothesis (Clarke): menstruation evolved as a means to eliminate defective embryos—high incidence of early pregnancy loss; high investment in each offspring, means want to eliminate losses early

5. Sexual Differentiation (Fill in the Blank):

The gene responsible for initiating male development in a fetus is the SRY gene. This gene codes for a protein called TDF which causes the medullas of the germinal ridge to develop into TESTES. There are two types of cells in the testes. The first type is called LEYDIG cells and they produce testosterone which causes the WOLFFIAN duct to develop into sex organs that connect the penis to the testes. The second type of cells is called SERTOLI cells and they produce a hormone called MIF which causes the MULLERIAN duct to regress in males. Under the action of testosterone, the genital folds become the SCROTUN while the genital tubercle becomes the PENIS. In females the folds become the LABIA and the tubercle becomes the CLITORIS. Females are not the default sex there are a number of genes such as DAX-1 that help regulate female development.

6. The Menstrual Cycle:

a. Label the lines on the graph with the correct hormone

Black= Estrogen, Blue= Progesterone, Red= Lutenizing Hormone)

b. Draw a line for the missing hormone in this graph and label that hormone. (Note: it is only the change of each hormone through time that is important, not the absolute levels of the hormones to one another.

Your line should closely mirror LH.

c. For each of the following events, place the corresponding number at the appropriate time on the graph.

d. As long as your letter is in the correct area on the graph, you will receive credit. The order is: D, F, B, A, C, E.

(1) The egg is released from the ovary

(2) Positive feedback loop for estrogen release begins

(3) Corpus luteum grows and develops

(4) Menstruation

(5) Corpus luteum degenerates

(6) A dominant follicle has been established

Essay 1. Discuss the human mating and marriage systems using an evolutionary perspective (30 pts).

• Trivers’ hypothesis: The sex that invests the most becomes a limiting resource for the sex that invests the least. This means that the sex investing the least will compete for the sex investing the most. In addition, the sex investing most can choose from members of the sex investing least.

• Important features of the human mating system: Concealed ovulation, low sex dimorphism, biparental care, sexual division of labor/food sharing, pair bonding, extended juvenile period, shorter IBI, maintenance of female kin alliances.

• Descriptions of great ape mating systems: (need to mention all 4 species below)

Orangutans- dispersed social system, concealed ovulation, huge sex dimorphism, sexual coercion

Gorillas- polygynous harems (many males bonded to one female), huge sexual dimorphism, very small estrous swelling, mating confined to ovulation

Chimpanzees- multi-male multi-female promiscuous mating system, large estrous swelling, lower sex dimorphism- males ¼ larger, female promiscuity may serve to confuse paternity and lower infanticide

Bonobos- multi-male, multi-female promiscuous mating system, large estrous swelling, lower sex dimorphism- males ¼ larger, female-female sexual activity (or strong female bonds).

• Marriage Systems

Monogamy: The Kung and other hunter-gatherers tend to practice serial monogamy. Since they cannot accumulate wealth and resources, there is little difference in reproductive potential amongst males and males cannot typically afford to have more than one wife. In 19th Cetury Ireland, parcels of land had been divided up until they were too small to be divided further to support more than one heir. Thus only one heir per family could marry and have their own family. Though we did say “not the US” and “ecology and/or culture”, you didn’t get two points for saying people in England marry monogamously because of religion as we had more pertinent examples in class and in the readings (i.e. this example does not show anything you have learned in class).

Polyandry: one of the examples of this in Tibet. Land parcels were unable to be subdivided and still capable of supporting a family therefore each family would marry a single daughter to a set of brothers who would help her work the land.

Polygyny- Datoga pastoralists (from sellen article) Kipsigis, Maasai. Male wealth measured in size of their livestock herds. Relates to the polygyny threshold model, whereby women may prefer to be the second wife of a wealthy man than the first wife of a poor man. Mormon Utah- another case where religion is an important part of the “ecology”- for this example you should explain that Mormon men in the US can theoretically support large families. Studies showed that- monogamously married women had more children but that polygynously married women had more grandchildren.

• Animal Morphology: Body size dimorphism is reduced in humans when you compare us to the other s. Men are only about 10% taller and 20% heavier than women. Generally when we look across the animal kingdom we find a pattern: monogamous animals tend to be monomorphic. In species where there are one male and a harem type system, we find much greater dimorphism- this is sexual selection working. Also we find another relationship in nature when we look at testes size relative to body weight. In species where females mate with multiple males, the males tend to have larger testes relative to body weight- this is true of a harem system or a monogamous system. In humans testes size by body weight is average suggesting minimal sperm competition in humans- (little multiple matings).

Essay 2

Contrast male and female reproductive systems. In your essay you should include the following:

1) Timing of pubertal development and the possible adaptive significance of these differences

2) Gamete production and how they influence reproductive strategies

3) The effect of energy balance on reproductive function in men and women and their evolutionary significance

1.

a. Human females on average complete puberty 2 years earlier than males The last stage of puberty that females go through is having fully fecund cycles. The order in which females develop is as follows: breast development, pubic hair, growth spurt, hip broadening, menstruation, fat deposition, and fully fecund cycles. In males however, testes enlargement and sperm production is the first stage of development followed by pubic hair, penis enlargement, growth spurt, axillary hair, facial hair, voice changes, broadening of shoulders/filling out.

b. The first stage of puberty development in males allows for reproduction whereas it is the last stage in females. One possible reason for this is that sperm production in males is not very costly. Doesn’t make sense to develop physically and engage in male-male competition if you aren’t able to reproduce. In females however, reproduction is costly and there is no point in getting pregnant if you aren’t developed enough to sustain/support it.

2.

a. Male germ cell differentiation occurs continuously in the seminiferous tubules of the testes throughout the life of a normal animal (divide continuously). So in males spermatogenesis is continuous. In women, mitotic division of germ cells occurs before birth (in females germ cells, called oogonia undergo mitosis and develop into primary oocytes and remain at a state of meiotic arrest (they begin the first meiotic development but do not complete it).

b. Females: Few big expensive gametes vs many small less expensive gametes

c. Women limited number of eggs, around 50 years go through menopause– no longer able to reproduce. Males continue to be fertile through old age

d. Sperm are mobile, ova are immobile.

e. Females initially provide greater investment in terms of gamete production, internal gestation and lactation. According to Trivers’ Parental Investment theory, “The sex that invests the most becomes a limiting resource for the sex that invests the least.” This means that the sex investing the least will compete for the sex investing the most, while the sex investing the most chooses from members of the sex investing least.

3.

a. Female ovarian function much more responsive to energetic factors than male testicular function.

b. Negative energy balance or high flux can depress ovarian function (estrogen and progesterone) making it less probable that conception will occur.

c. Female RS is limited by access to resources. Having ovarian function tied so closely to energetics is adaptive because it could be potentially very costly to have an ill-timed conception- high costs of carrying the pregnancy to term, lactation, rearing the child postnatally. It is usually better to postpone conception during tough periods in favor of investing in oneself.

d. Women who grow up in chronically poor environments tend to establish set points for reproductive function that are lower than Westerners- unclear whether these differences bear on fecundity.

e. Testosterone in men decreases only under fairly severe stress and cessation of sperm production almost never occurs.

f. Male RS is limited by access to females. Since the only obligate male investment in offspring is sperm, it is adaptive for males to maintain reproductive function even in the face of energetic stress; the potential opportunity to increase RS at anytime far outweighs any costs associated with making sperm.

g. As in women, men who grow up under chronic developmental stress (such as the Ache) tend to have lower T levels. This keeps levels of energetically expensive muscle mass fairly low but maintains normal sperm production.

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