SECTION TWO SHORT ANSWER QUESTIONS

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1 SECTION TWO SHORT ANSWER QUESTIONS Q1. Assume that we have developed advanced methods of artificial fertilization that allow us to create embryos from the combined genetic material of either two sperm cells or two egg cells (rather than from the combined genetic material of one sperm and one egg cell). Using these methods, would it be possible a. For two men to have a daughter? (2 points) b. For two women to have a son? (2 points) (very briefly justify your answers no points for only yes or no ) This is pretty straight-forward: a) YES: sperm cells contain either an X or a Y chromosome, thus a combination of two X-sperms - resulting in an XX (female) child - is possible; b) NO: egg cells always contain an X chromosome (never a Y), so no XY (male) combination is possible. However, I also accepted as an alternative b) YES: although egg cells always contain an X chromosome, they might contain an additional (translocated) SRY gene, which would trigger male development in an XX male. Note, though, that this argument is somewhat problematic: according to this logic, the person carrying the additional SRY gene would also be an XX male, not (as requested) a woman! So anyone producing this answer got only 1 point (out of 2) for correctness, but then got 1 further point for out-of-the-box thinking. Q2. Why are negative feedback loops important in homeostasis? (3 points) Again, a fairly straight-forward question: Homeostasis = keeping the organism s internal environment within a critical range - if it shifts too far in either direction, it must be brought back to set point (i.e., too much of X: downregulate; too little of X: up-regulate); Negative feedback loop (NFL) = an arrangement whereby a system uses its own output to down-regulate its behaviour (i.e., presence of output reduces output production); Therefore: NFLs can be used in homeostatic processes as that component that down-regulates the system (something else is needed to up-regulate it). Most answers were considerably more condensed than this one. However, full marks were given as long as they got the crucial point across that NFLs are only one component of homeostasis (i.e., they are not the same as homeostatic processes, nor are they on their own sufficient to implement homeostatic processes). Generally, no points were given for variants of "because homeostatic processes need negative feedback loops", no matter how technically-sounding this was presented (e.g., "because negative feedback loops enable oscillating behaviour, or "negative feedback loops allow the system to remain within a critical range etc.). Note that the question asked why are NFLs important for homeostasis. Therefore, any answer that boils down to because they are important for homeostasis fails to add any information!

2 Q3. Draw a flow-chart (i.e., labelled boxes and arrows) showing the sexual development from conception to puberty of a. a normal human male (4 points) b. a chromosomally male human with complete androgen insensitivity (4 points) A purely knowledge-based question: a) See lecture handout 3, page 13 (right-hand side) b) An adaptation of the same graph as follows: 1. Up to and including the stage testes release androgens, everything is the same as in (a) including release of MIH hence, Müllerian duct degenerates instead of developing into (part of the) internal female reproductive organs; 2. Androgens released by the testes are not recognized by the body, therefore: Wolffian duct degenerates instead of developing into (part of the) internal male reproductive system; Testosterone is transformed into DHT (recall: this is done by an enzyme, not by testosterone receptors, so is not affected by the disorder) DHT is still a form of testosterone, so won t be recognized by the urogenital tissue either hence, urogenital groove develops according to female default; 3. At puberty, the body of course still follows the female default, thus: Breasts develop, Although there is, of course, no ovulation (seeing as the person has testes, not ovaries); 4. So overall, the outcome is an infertile woman (not a person with intersex appearance, as the question specifically stated complete AIS). Q4. Draw a flow-chart (i.e., labelled boxes and arrows) showing post-traumatic stress disorder (PTSD) as resulting from a positive feedback loop. (4 points) This was discussed only briefly in lecture 5, as the negative flip-side of the social bonding through stress model: stress triggers adrenaline release adrenaline improves memory - particularly strong or vivid memories of a negative event might then trigger renewed adrenaline release... Thus anyone getting this answer right demonstrated that they can use (not merely regurgitate) the information learned in the lecture (alternatively, they demonstrated good memory of Year 1, where this example was discussed in more detail).

3 Q5. In the general population it is widely believed that boys are better than girls at math and physics, and genetically determined differences in male versus female brains are claimed to be the reason for this perceived discrepancy. Is it possible to reconcile this position with the finding that although girls in mixedsex schools tend to get lower grades in math and physics than boys, girls in single-sex schools tend to do just as well as their male peers? (4 points; briefly justify your answer no points for only yes or no ) There s no right or wrong answer here the question assesses your ability to argue coherently within a psychobiological / evolutionary framework. NO. - Let s assume that the only difference between the two situations (single vs. mixed-sex schools) is the presence of boys. - If math skills are genetically determined, then the presence or absence of such an unrelated factor could not affect them. - Therefore, the finding that it does affect them suggests that gender differences in math skills are not genetically determined. - (Maybe gender stereotypes create gender differences: girls in mixed schools are constantly reminded that they are expected to be bad at math, which makes them perform poorly even though they could do better.) *** OR *** YES. - One could argue that the two types of schools (single- vs. mixed-sex schools) are likely to differ not only in the presence or absence of opposite-sex pupils, but also in other, relevant aspects (particularly, in the amount or intensity of math and physics teaching). - Let s assume that everyone gets the same amount of math and physics teaching, except for girls in single-sex schools, who receive more. - If this is the case, then the fact that they do as well in math and physics as boys simply means that they need more training to achieve the same performance. - This would be entirely consistent with the assumption that girls are genetically predisposed to be less good at math than boys are. Either answer would have received full marks (although the first one is better than the second one, as it makes fewer additional assumptions: for the second argument to work, you have to make the additional assumptions that the schools differ in other, relevant aspects. This assumption was not specified in (or required by) the question! However, this is fine as long as you re being explicit about it. In contrast, no points were awarded for answers based on (variants of) We already know for a fact that girls brains are genetically determined to do less well in certain tasks, therefore, it has to be the case that... : whatever else is said (whether it s a YES or a NO answer), it cannot possibly rescue this, because this is a circular argument (hence, a non-argument)! In case you wonder why, this is the reason: - How do we know about brains and their skills, genetically determined or not? Brains aren t like cars: we can t just take them apart and look how they work! - That leaves us with only one other way: we observe how people perform various tasks. o It s important to be perfectly clear about this: we know nothing about someone s brains except what we learn from their task performance! o Or to be more precise: we know nothing about how people s brains work, we can only make reasonable assumptions, based on their task performance.

4 - Which means that we cannot discount some task performance just because it doesn t fit with our prejudice! - But this is exactly what the above argument does. It basically claims that even if girls do as well as boys, we still know that they don t do as well as boys hardly a sensible argument! Similarly, no points for YES, because genetically determined sex differences need to be activated through social learning. Why no points for this? Because it translates to Girls are genetically determined to be inferior, but if they aren t taught that they re inferior, they will fail to be inferior. Again, an argument that really makes no sense. Q6. Draw a graph representing the relationship between cognitive performance (yaxis) and dopamine levels (x-axis). (4 points) Another straight-forward knowledge-based question: the relationship is represented by an inverted u-shaped curve:

5 Q7. During particularly stressful times, we often suffer from sleep problems: we find it hard to fall asleep, and the sleep we do manage to get is never very deep. This seems to be a maladaptive behaviour, depriving us of rest when we need it most. Could it nevertheless reflect an evolutionary beneficial adaptation? (If so, how, if not, why not?) (5 points) Like Q5 above, this one invited you to speculate, and to produce a good argument. In addition, you should have picked up on some of the features discussed in the sleep lecture. Full marks would have been given, for instance, for something like: Yes, it could reflect an evolutionary beneficial adaptation. - In our evolutionary past, stress might mostly have come in the form of a predator being close. - If a predator is close, being vigilant is more important than being well-rested. - If stress prevents us from going into slow-wave sleep, then this would mean that we are more likely to sense (hear, smell) an approaching predator, and to respond appropriately. - Specifically, it would reduce the likelihood of entering REM sleep (during which we might be particularly unresponsive to our environment, as we are experiencing vivid dreams while being effectively paralyzed). - However, sacrificing sleep for increased vigilance can only be a short-term solution, as in the long run, continued sleep deprivation is likely to result in physical and cognitive impairment (and possible death). Few people seemed to have fundamental problems with this question, so I assume that no further explanation or clarification is necessary. Q8. In four or fewer sentences, provide an evolutionary argument for the origins of altruism. (5 points) And one final straight-forward knowledge questions: Altruism can evolve based on kin selection and reciprocity. Kin selection means to help those to whom we are closely genetically related: through their reproductive success, our shared genes are passed on to the next generation. Reciprocity involves helping individuals who can help us in return, thus increasing our own reproductive success (this works at the group level as well, as groups that help one another can outcompete groups where the individuals compete internally).