Test your understanding of Evolution

[ronburgundy]

Hello nerds. I am helping a friend to refine some questions designed to test people's understanding of natural selection. I am interested in your feedback about the quality of these questions and answer options. Note that these are not intended to be comprehensive and cover all aspects of evolution, and should be somewhat difficult for a total novice. Besides critiques, I am interested in which one's you got wrong and what you think your general level of expertise on evolution is. Questions that Biology Ph.Ds get wrong indicate a problem for the test.

Answers are hidden after each Q.


1. Imagine that pollution caused the tree trunks in the countryside to become covered in black soot and ash. Years later, scientists notice that the local moths are also darker than they used to be. Which of the following would be a good evolutionary explanation for this?
a) The moths changed to a darker color in order to blend in with their surroundings
b) The moths that happened to be born darker were more likely to survive and reproduce
c) The lighter moths migrated to a different habitat with lighter colored trees
d) Evolution would not be relevant to this situation

Show

b

2. A species of woodpeckers have one-inch long beaks, on average, and their main food source are bugs that live inside trees with bark that is about one and a half inches thick. Compared to its parents, the offspring of any two woodpeckers should be born with which of the following features?
a) A shorter beak, because one generation is not long enough for adaptive variations
b) A longer beak, because the offspring will adapt to what is necessary for their survival
c) Either a shorter or longer beak is equally likely, because variation from parents is random
d) All offspring would have to have the exact same length beak as their parents

Show

c

3. A high-school basketball team shoots more accurate shots per game this season than last season. Which explanation for this change is the LEAST analogous to (LEAST similar to) how features of a population are affected by selection pressures?
a) More students tried out for the same number of spots on the team this year
b) All the players tried to get better by practicing harder.
c) Several very talented players moved into town.
d) The coach made it more difficult to qualify for the team.

Show

b

4. It’s safe to assume that it is advantageous to be able to see well during both day and night. However, humans have a difficult time seeing in the dark, even though some other animals do not. Why don’t all animals have all the traits that would be most adaptive for their survival?
a) If an animal lacks a trait, it means it would not be adaptive for its environment
b) Natural selection makes sure that no animal is perfect so that there is competition
c) Alleles for some traits were never randomly generated within that species
d) They will eventually, there just hasn’t been enough time yet
 

Show

c

5. The ancestors of whales had legs, but eventually and lost them over the years. Suppose tortoises didn’t used to have hard shells, but later developed them. Which can be explained by the principles of evolution?
a) Whales losing their legs, because evolution favors simplicity
b) Tortoises developing hard shells because evolution favors complexity
c) Tortoises, because evolution explains acquiring new traits, not the loss of traits
d) Both, as they can improve fitness in both cases

Show

d

6. Over time, it appears that some viruses, such as tuberculosis, can develop resistance to commonly prescribed treatments. How would the theory of evolution explain that some illnesses are able to develop drug resistance?
a) Such illnesses use reactive, targeted changes to protect themselves from drugs
b) Some virus cells get lucky through mutations that happen to protect them from drugs
c) The chemicals in the drugs change the chemistry of viruses and make them resistant
d) All virus cells that have been exposed to the drug become immune

Show

b

 

[ryan]

2. has the answer in the question. It is more about how good they are at taking tests while possibly knowing nothing about evolution.

For 3. d seems to be more like an answer analogous to evolution. The answer b seems to imply that fitness for the environment is more likely acquired than evolved.

I probably have an average understanding of evolution. I did well in grade 12 biology, but that's all I got.

 

[Elixir]

The third question is shaky IMO.
"Several talented new players moved to town" assumes a previous limit to the eligibility of individuals to become part of the team, now removed by physical circumstance. That would be analgous to a change in an organism's niche and the selective pressures therein. I think he needs another analogy.

 

[bilby]

I agree with Elixir, question 3 relies on a rather tortured metaphor, and could easily be misinterpreted.

I am not very comfortable with the 'Suppose' element in question 5; It seems to introduce opinion to a question of fact. If I suppose that tortoises didn’t used to have hard shells, but later developed them, then the mechanism for this is whatever I supposed it to be.

And in question 6, Tuberculosis is a Mycobacterial infection. It's not caused by a virus. In general, drug resistance is less commonly developed by viruses than it is by bacteria, although there are common examples of drug resistant virus strains. Influenza strains that are becoming resistant to Neurominidase inhibitors are a good example, if you really want to use a virus in the question; Or of course you could simply change 'virus' to 'bacterium' throughout.

 

[ronburgundy]

Thanks to all for feedback. Q 3 has been the one I've had most trouble fixing to make it work. I agree it should just be scrapped.

2. has the answer in the question. It is more about how good they are at taking tests while possibly knowing nothing about evolution.

Ryan,
I'm having trouble seeing where the answer is in the question for #2.
The question sets up the situation that would make a longer beak more adaptive. But this is actually misleading people to pick the wrong answer b, if they have the misconception that what is potentially adaptive once it emerges actually determines what variations emerge in the first place. The correct answer of "c" requires knowing that single generation variations and selection pressures interact which each other rather than the latter directly determining the former. The incorrect answer "d" might be selected by people who don't even understand genetic variance at all.

 

[James Brown]

I got them all right except Q3. Just because a bunch of talented players moved to town doesn't mean they tried out for the team, or that the coach would necessarily pick them for the team (grades too low, etc.)

As for my level of expertise, I was educated in high school by a Creationist, so all my exposure to Natural Selection was on how to debunk it. Then for fifteen years I barely thought about the issue, not working in biology. After I deconverted, I've been educating myself on the side and participating in "Evolution vs. Creationism" discussion online. There's still a lot I have to learn, but I think I'm getting the basics.

Now if this was a test about genetics, I'm quite sure I would have failed it. I can't wrap my head around that stuff.

 

[Jarhyn]

I got then all, but I have a gripe about question 4. The actual answer is 'some traits have a high cost associated with their benefit, and evolution will favor individuals mutated to drop an expensive trait when lifestyle mutations make the cost unnecessary.'

IOW, an eye can only have so many sensors in it.

 

[untermensche]

Question #2.

c) Either a shorter or longer beak is equally likely, because variation from parents is random

We have no way to derive odds like that.

It may in fact be the case that a mutation that leads to a longer beak is more likely.

 

[Loren Pechtel]

Question #2.

c) Either a shorter or longer beak is equally likely, because variation from parents is random

We have no way to derive odds like that.

It may in fact be the case that a mutation that leads to a longer beak is more likely.

You flunk.

Evolution has no idea that longer beaks are desired. The beak length will vary based on the genetics, unless it's controlled by a simple gene (for example, eye color) the effect will appear random.

Evolution has no effect on the reproductive process. Rather, the short-beaked birds have a harder time finding food and thus are less likely to reproduce in the first place.

 

[ryan]

Thanks to all for feedback. Q 3 has been the one I've had most trouble fixing to make it work. I agree it should just be scrapped.

2. has the answer in the question. It is more about how good they are at taking tests while possibly knowing nothing about evolution.

Ryan,
I'm having trouble seeing where the answer is in the question for #2.
The question sets up the situation that would make a longer beak more adaptive. But this is actually misleading people to pick the wrong answer b, if they have the misconception that what is potentially adaptive once it emerges actually determines what variations emerge in the first place. The correct answer of "c" requires knowing that single generation variations and selection pressures interact which each other rather than the latter directly determining the former. The incorrect answer "d" might be selected by people who don't even understand genetic variance at all.

Yeah, sorry, I missed the "on average" part.

 

[rjh01]

4. It’s safe to assume that it is advantageous to be able to see well during both day and night. However, humans have a difficult time seeing in the dark, even though some other animals do not. Why don’t all animals have all the traits that would be most adaptive for their survival?
a) If an animal lacks a trait, it means it would not be adaptive for its environment
b) Natural selection makes sure that no animal is perfect so that there is competition
c) Alleles for some traits were never randomly generated within that species
d) They will eventually, there just hasn’t been enough time yet

I think question 4 needs a better answer. The supplied answer is not complete. It is not chance that they were not generated.

My answer would be that there would be no need for most species to see well in both day and night. If a species can see well at night time then its colour vision would be poor. That would be OK as it would be active at night time. There are some species that see colour well (think reptiles). These all sleep at nighttime so they have no need to be able to see at night. Then there are other species like primates who used to have good night vision to avoid the dinosaurs. Then started living in the trees and need to tell the difference between a ripe and unripe fruit, so they needed good colour vision. They have not yet evolved eyesight as good as reptiles but at least it is good enough for the purpose.

Some reptiles can see in the UV range and have four primary colours. Flowers look different in the UV range.

 

[rjh01]

Had another look at question 2. All answers are incorrect. All birds stave to death without breeding as they cannot get access to the bugs. Suggest you say that the bark can be between 3/4 and 1 1/2 inches thick. That way some do survive. If they have other food then they do not eat bugs.

 

[Peez]

Hello nerds. I am helping a friend to refine some questions designed to test people's understanding of natural selection. I am interested in your feedback about the quality of these questions and answer options. Note that these are not intended to be comprehensive and cover all aspects of evolution, and should be somewhat difficult for a total novice. Besides critiques, I am interested in which one's you got wrong and what you think your general level of expertise on evolution is. Questions that Biology Ph.Ds get wrong indicate a problem for the test.

I have one of those, in evolutionary ecology in fact.

1. Imagine that pollution caused the tree trunks in the countryside to become covered in black soot and ash. Years later, scientists notice that the local moths are also darker than they used to be. Which of the following would be a good evolutionary explanation for this?
a) The moths changed to a darker color in order to blend in with their surroundings
b) The moths that happened to be born darker were more likely to survive and reproduce
c) The lighter moths migrated to a different habitat with lighter colored trees
d) Evolution would not be relevant to this situation

I don't have a big problem with this one, but open ended questions like these can be problematic. Answer "a" might be OK, depending on how one interprets it (in some sense, the population of moths could have "changed to a darker color", and in some sense it could have been "in order to blend in with their surroundings"). Although answer "c" seems unlikely, it is not entirely impossible from the point of view of evolution (one needs to know a little about moth biology here). Answer "d" might be considered if the change in colour was not genetically based.

2. A species of woodpeckers have one-inch long beaks, on average, and their main food source are bugs that live inside trees with bark that is about one and a half inches thick. Compared to its parents, the offspring of any two woodpeckers should be born with which of the following features?
a) A shorter beak, because one generation is not long enough for adaptive variations
b) A longer beak, because the offspring will adapt to what is necessary for their survival
c) Either a shorter or longer beak is equally likely, because variation from parents is random
d) All offspring would have to have the exact same length beak as their parents

This question is fine, but untermensche is correct: there might be something about the determination of beak length that makes long (or short) beaks more likely. However, knowing nothing about that, it is fair to state that there is no reason to expect the beak length to be longer in the offspring.

3. A high-school basketball team shoots more accurate shots per game this season than last season. Which explanation for this change is the LEAST analogous to (LEAST similar to) how features of a population are affected by selection pressures?
a) More students tried out for the same number of spots on the team this year
b) All the players tried to get better by practicing harder.
c) Several very talented players moved into town.
d) The coach made it more difficult to qualify for the team.

This seems fine to me.

4. It’s safe to assume that it is advantageous to be able to see well during both day and night. However, humans have a difficult time seeing in the dark, even though some other animals do not. Why don’t all animals have all the traits that would be most adaptive for their survival?
a) If an animal lacks a trait, it means it would not be adaptive for its environment
b) Natural selection makes sure that no animal is perfect so that there is competition
c) Alleles for some traits were never randomly generated within that species
d) They will eventually, there just hasn’t been enough time yet

I don't like this one, it misses a very important consideration in evolution: trade-offs. We cannot assume that changes in our eye that would give us better night vision would not reduce our day vision in some way (see also 'balancing/stabilizing selection'). I would also avoid stating that "some other animals do not... have a difficult time seeing in the dark", that is somewhat simplistic. There certainly are many animals that can see in the dark much better than we can, but we should not imply that nocturnal animals can see in the dark as well as diurnal animals can see in the daylight.
 

5. The ancestors of whales had legs, but eventually and lost them over the years. Suppose tortoises didn’t used to have hard shells, but later developed them. Which can be explained by the principles of evolution?
a) Whales losing their legs, because evolution favors simplicity
b) Tortoises developing hard shells because evolution favors complexity
c) Tortoises, because evolution explains acquiring new traits, not the loss of traits
d) Both, as they can improve fitness in both cases

This is fine.

6. Over time, it appears that some viruses, such as tuberculosis, can develop resistance to commonly prescribed treatments. How would the theory of evolution explain that some illnesses are able to develop drug resistance?
a) Such illnesses use reactive, targeted changes to protect themselves from drugs
b) Some virus cells get lucky through mutations that happen to protect them from drugs
c) The chemicals in the drugs change the chemistry of viruses and make them resistant
d) All virus cells that have been exposed to the drug become immune

It was mentioned that tuberculosis is caused by a bacterium rather than a virus, I would add that a virus is not cellular (answer "b"). Otherwise this question should be good.

Peez

 

[Peez]

Had another look at question 2. All answers are incorrect. All birds stave to death without breeding as they cannot get access to the bugs. Suggest you say that the bark can be between 3/4 and 1 1/2 inches thick. That way some do survive. If they have other food then they do not eat bugs.

I agree, but it is also possible that beak length need not exceed bark thickness for feeding to occur. It would be useful to clarify the question somewhat.

Peez

 

[T.G.G. Moogly]

4. It’s safe to assume that it is advantageous to be able to see well during both day and night. However, humans have a difficult time seeing in the dark, even though some other animals do not. Why don’t all animals have all the traits that would be most adaptive for their survival?
a) If an animal lacks a trait, it means it would not be adaptive for its environment
b) Natural selection makes sure that no animal is perfect so that there is competition
c) Alleles for some traits were never randomly generated within that species
d) They will eventually, there just hasn’t been enough time yet

I think question 4 needs a better answer. The supplied answer is not complete. It is not chance that they were not generated.

My answer would be that there would be no need for most species to see well in both day and night. If a species can see well at night time then its colour vision would be poor. That would be OK as it would be active at night time. There are some species that see colour well (think reptiles). These all sleep at nighttime so they have no need to be able to see at night. Then there are other species like primates who used to have good night vision to avoid the dinosaurs. Then started living in the trees and need to tell the difference between a ripe and unripe fruit, so they needed good colour vision. They have not yet evolved eyesight as good as reptiles but at least it is good enough for the purpose.

Some reptiles can see in the UV range and have four primary colours. Flowers look different in the UV range.

Maybe Peez can correct my ignorance but I do not see a good answer here. The best answer is (a) because the environment rules. Clearly, night vision did not confer a survival advantage when our eyes were being selected for. There could be a myriad of reasons for this but that we do not have night vision means it was not the best way to survive given the environment. One might add that by this time significantly better night vision was no longer an option even via mutation. We had already branched eons ago.

 

[Peez]

There are some species that see colour well (think reptiles).

...and some mammals, particularly primates.

These all sleep at nighttime so they have no need to be able to see at night.

While diurnal animals don't usually need to see at night, there are times when it can be useful. I agree that selection favouring night vision would be much weaker for nocturnal animals.

Then there are other species like primates who used to have good night vision to avoid the dinosaurs.

I believe that primates evolved after dinosaurs went extinct.

Then started living in the trees and need to tell the difference between a ripe and unripe fruit, so they needed good colour vision.

Indeed, a very important point (as an aside, binocular vision was also favoured: good for judging distance to a branch in a tree).

They have not yet evolved eyesight as good as reptiles but at least it is good enough for the purpose.

Primates have worse eyesight than "reptiles"? I am curious about what aspect of vision is being considered, and the source of this information. Birds certainly tend to generally have excellent vision (considering a few factors), but I had not read that other reptiles were notable in vision.

Some reptiles can see in the UV range and have four primary colours.

It has been suggested that tetrachromacy (having photoreceptors for four different colours) may have been ancestral for chordates, and that mammals lost one in their evolution. Just be careful about the term "primary colours", since to many people this refers to blue, red, and yellow (the three colours that our eyes can detect are approximately blue, red, and green).

Flowers look different in the UV range.

Bees also see into the UV range, many flower patterns are invisible to us but visible to the animals that matter to them.

Peez

 

[Peez]

I think question 4 needs a better answer. The supplied answer is not complete. It is not chance that they were not generated.

My answer would be that there would be no need for most species to see well in both day and night. If a species can see well at night time then its colour vision would be poor. That would be OK as it would be active at night time. There are some species that see colour well (think reptiles). These all sleep at nighttime so they have no need to be able to see at night. Then there are other species like primates who used to have good night vision to avoid the dinosaurs. Then started living in the trees and need to tell the difference between a ripe and unripe fruit, so they needed good colour vision. They have not yet evolved eyesight as good as reptiles but at least it is good enough for the purpose.

Some reptiles can see in the UV range and have four primary colours. Flowers look different in the UV range.

Maybe Peez can correct my ignorance but I do not see a good answer here. The best answer is (a) because the environment rules. Clearly, night vision did not confer a survival advantage when our eyes were being selected for. There could be a myriad of reasons for this but that we do not have night vision means it was not the best way to survive given the environment. One might add that by this time significantly better night vision was no longer an option even via mutation. We had already branched eons ago.

I touched on this in my earlier reply, but... although your thinking is not unreasonable, there are a couple of things that should be considered. It is quite possible that having better night vision would have been an advantage for our ancestors, just not a big advantage. Any change that made our eyes better at night but worse in the day would tend to be selected against, because the fitness disadvantage to having worse vision during the day would outweigh any small advantage that improved night vision would have provided. Whether better night vision could evolve now is an open question, but I see no reason why it could not. I do agree that since our eyes have evolved a great deal, certain evolutionary pathways may have been 'shut off' for us. However, there is likely still potential for evolution of our vision.

Peez

 

[ronburgundy]

Maybe Peez can correct my ignorance but I do not see a good answer here. The best answer is (a) because the environment rules. Clearly, night vision did not confer a survival advantage when our eyes were being selected for. There could be a myriad of reasons for this but that we do not have night vision means it was not the best way to survive given the environment. One might add that by this time significantly better night vision was no longer an option even via mutation. We had already branched eons ago.

I touched on this in my earlier reply, but... although your thinking is not unreasonable, there are a couple of things that should be considered. It is quite possible that having better night vision would have been an advantage for our ancestors, just not a big advantage. Any change that made our eyes better at night but worse in the day would tend to be selected against, because the fitness disadvantage to having worse vision during the day would outweigh any small advantage that improved night vision would have provided. Whether better night vision could evolve now is an open question, but I see no reason why it could not. I do agree that since our eyes have evolved a great deal, certain evolutionary pathways may have been 'shut off' for us. However, there is likely still potential for evolution of our vision.

Peez

Peez, You raise a great point about trade-offs rooted in physiological constraints that impede one adaptive trait because it cannot exist without impairing another adaptive trait.
However, I don't see that as being consistent with any of the answers. So, that leaves option C as the only option that is at least one (but not the sole) explanation for why an infinite number of traits that would be a net advantage to the organism don't exist.

Question 4 is trying to get at the idea that evolution is not teleological or directional toward perfection, and that whether the allele for a trait ever appears in the first place to be selective for has little to do with whether the trait would be adaptive.

Answer (a) is wrong because it presumes that merely being adpative is suffient by itself for a specific variation in alleles to emerge and then be selected for. Only that level of sufficiency, would imply that the non-existence of a trait means it wouldn't be adaptive. Infinite numbers of variations in traits for every organism would be highly adaptive, yet those organisms lack those traits, because adaptiveness only operates after the allele emerges due to factors having nothing to do with whether the phenotypic effects are adaptive. This also makes answers (b) and (d) wrong.

Answer c is (to my understanding) is at least one if not THE primary reason why most of the infinite # of potential adaptive traits don't exist in every organism where they would be adaptive.

Night vision is just being used as an example, and maybe its not a good one for the reasons you gave. What if the question said the following:

Which of the following is a reason why all animals do NOT have all of the traits that would be most adaptive for their survival?

Thanks again to all this feedback.

 

[Treedbear]

I think you should explain in the beginning that the answers should be the one that best illustrates the principles of evolution. You hinted at this in several, but not all. If you did that I think most of the criticism is corrected for. That said I'll do some nitpicking of my own. I got two wrong.

2. A species of woodpeckers have one-inch long beaks, on average, and their main food source are bugs that live inside trees with bark that is about one and a half inches thick. Compared to its parents, the offspring of any two woodpeckers should be born with which of the following features?

I chose

a) A shorter beak, because one generation is not long enough for adaptive variations

After reading it several times I decided that "shorter" meant no significant change in size since it remains shorter than what is required for adaptation, and one generation is clearly insufficient for evolution to take place. The beak actually getting smaller would make no sense whatsoever.

4. It’s safe to assume that it is advantageous to be able to see well during both day and night. However, humans have a difficult time seeing in the dark, even though some other animals do not. Why don’t all animals have all the traits that would be most adaptive for their survival?

I narrowed it down to two:

c) Alleles for some traits were never randomly generated within that species
d) They will eventually, there just hasn’t been enough time yet

The choice is somewhat ambiguous. With c) the necessary alleles could have been generated but not propagated sufficiently or they were otherwise suppressed. For d) it seems reasonable that given enough time and the right environment the traits would evolve randomly, at least in principle. And it seems this would include the generation of alleles.

 

[Peez]

There has been quite a bit of discussion of question 4, let me collect all of it:

ronburgundy:
4. It’s safe to assume that it is advantageous to be able to see well during both day and night. However, humans have a difficult time seeing in the dark, even though some other animals do not. Why don’t all animals have all the traits that would be most adaptive for their survival?
a) If an animal lacks a trait, it means it would not be adaptive for its environment
b) Natural selection makes sure that no animal is perfect so that there is competition
c) Alleles for some traits were never randomly generated within that species
d) They will eventually, there just hasn’t been enough time yet
c

Jarhyn:
I got then all, but I have a gripe about question 4. The actual answer is 'some traits have a high cost associated with their benefit, and evolution will favor individuals mutated to drop an expensive trait when lifestyle mutations make the cost unnecessary.'
IOW, an eye can only have so many sensors in it.

Note that Jarhyn raises here the same issue that I bring up later.

rjh01:
I think question 4 needs a better answer. The supplied answer is not complete. It is not chance that they were not generated.
My answer would be that there would be no need for most species to see well in both day and night. If a species can see well at night time then its colour vision would be poor. That would be OK as it would be active at night time. There are some species that see colour well (think reptiles). These all sleep at nighttime so they have no need to be able to see at night. Then there are other species like primates who used to have good night vision to avoid the dinosaurs. Then started living in the trees and need to tell the difference between a ripe and unripe fruit, so they needed good colour vision. They have not yet evolved eyesight as good as reptiles but at least it is good enough for the purpose.
Some reptiles can see in the UV range and have four primary colours. Flowers look different in the UV range.

Peez:
I don't like this one, it misses a very important consideration in evolution: trade-offs. We cannot assume that changes in our eye that would give us better night vision would not reduce our day vision in some way (see also 'balancing/stabilizing selection'). I would also avoid stating that "some other animals do not... have a difficult time seeing in the dark", that is somewhat simplistic. There certainly are many animals that can see in the dark much better than we can, but we should not imply that nocturnal animals can see in the dark as well as diurnal animals can see in the daylight.

joedad:
Maybe Peez can correct my ignorance but I do not see a good answer here. The best answer is (a) because the environment rules. Clearly, night vision did not confer a survival advantage when our eyes were being selected for. There could be a myriad of reasons for this but that we do not have night vision means it was not the best way to survive given the environment. One might add that by this time significantly better night vision was no longer an option even via mutation. We had already branched eons ago.

Peez:
I touched on this in my earlier reply, but... although your thinking is not unreasonable, there are a couple of things that should be considered. It is quite possible that having better night vision would have been an advantage for our ancestors, just not a big advantage. Any change that made our eyes better at night but worse in the day would tend to be selected against, because the fitness disadvantage to having worse vision during the day would outweigh any small advantage that improved night vision would have provided. Whether better night vision could evolve now is an open question, but I see no reason why it could not. I do agree that since our eyes have evolved a great deal, certain evolutionary pathways may have been 'shut off' for us. However, there is likely still potential for evolution of our vision.

ronburgundy:
Peez, You raise a great point about trade-offs rooted in physiological constraints that impede one adaptive trait because it cannot exist without impairing another adaptive trait.
However, I don't see that as being consistent with any of the answers.

I agree, that’s why I didn’t like it.

So, that leaves option C as the only option that is at least one (but not the sole) explanation for why an infinite number of traits that would be a net advantage to the organism don't exist.

Answer “c” could be a reason, at least it is not unimaginable, but everything we know suggests that this is not the limiting factor. There is a danger in thinking of there being an allele for a particular trait (though this can be a useful simplification in some contexts).

In this context, it is more productive to think of there being genetic variance for a trait. In any population we would expect to find some phenotypic variance (some individuals have better night vision than others). Typically some of that phenotypic variance is caused by genetic variance (some alleles, or combinations of alleles, give carriers better night vision than what other individuals enjoy). If having better night vision is associated with higher fitness (average reproductive success is higher for those having better night vision), then we would expect better night vision to evolve.

Note that having better night vision does not automatically translate into higher average fitness, even if individuals find it useful to see at night from time to time. One simplistic example is that having more rods (black-and-white light sensors in the retina) and fewer cones (colour sensors in the retina) will tend to give you better night vision (because rods are better at night vision than cones) but worse day vision (because you would be worse at detecting colours during the day). If the disadvantage of this day vision outweighs the advantage of the night vision, then overall those with the better night vision would tend to suffer lower fitness.

Question 4 is trying to get at the idea that evolution is not teleological or directional toward perfection, and that whether the allele for a trait ever appears in the first place to be selective for has little to do with whether the trait would be adaptive.

Those are important points to make. I think that question 2 touches on this as well. An interesting example is sickle cell disease and malaria.

Answer (a) is wrong because it presumes that merely being adpative is suffient by itself for a specific variation in alleles to emerge and then be selected for. Only that level of sufficiency, would imply that the non-existence of a trait means it wouldn't be adaptive. Infinite numbers of variations in traits for every organism would be highly adaptive, yet those organisms lack those traits, because adaptiveness only operates after the allele emerges due to factors having nothing to do with whether the phenotypic effects are adaptive. This also makes answers (b) and (d) wrong.

Answer c is (to my understanding) is at least one if not THE primary reason why most of the infinite # of potential adaptive traits don't exist in every organism where they would be adaptive.

It is always possible that some variation has simply not been generated in a particular population, but we have no evidence that this is a general limit on evolution. Rather it is trade-offs, the presence of fitness valleys, and physical limits that are likely responsible for organisms seeming to lack potentially useful adaptations. You can read about fitness valleys under fitness landscapes, and by physical limits I am referring to the realities of physics, chemistry, and biology that limit what is possible.

Night vision is just being used as an example, and maybe its not a good one for the reasons you gave. What if the question said the following:

Which of the following is a reason why all animals do NOT have all of the traits that would be most adaptive for their survival?

This is a good question, but the answer can be complex so I would recommend something more focussed. I would also recommend approaching the issue of mutation with something like the woodpecker question. The idea evolution is always limited because it is waiting for mutation to generate just the right allele is a common misconception. It certainly may occur in some cases (it is hard to say how often), but it would be misleading to invoke it as a general pattern.

Thanks again to all this feedback.

It is my pleasure, just please excuse my comments if they sound too negative: I like this project and am only dwelling on the problems I find to help it move forward.

Peez