I assume this is a reference to the Isaac Newton quote "If I have seen farther than others, it is because I have stood on the shoulders of giants.". But my friend Megan passed this along to me, which is essentially a call to post about a classic paper in your field and the contributions it's made.
The papers which have had the most direct effect on my science have been relatively more recent, but thankfully, I do know some useful older ones as well. If I were feeling more ambitious, I'd tackle Sewall Wright's 1932 paper which laid out shifting balance theory, but that's not going to fit into my current time scheme. So I'll instead go with Lederberg and Lederberg's March 1952 classic Replica Plating and Indirect Selection of Bacterial Mutants in the Journal of Bacteriology
Though it's hard to think of it at the moment, at the time this paper was written there was controversy over the origin of mutations. Some people felt that mutations were always arising spontaneously. Others felt that mutations which conferred adaptation to a specific condition would be brought about by introduction of that condition. For example, if a cell were subjected to an increased salt concentration, mutations which enabled it to deal with a high salt concentration (maybe changes in ionic transporters, changes in the internal salt concentration, changes in detoxification machinery, etc) would be induced, and thus occur more frequently than they would in a cell not subjected to salt stress. Thought this may seem strikingly teleological, I feel it's important to remember that this was before the double helix nature of DNA had been demonstrated, so it was a time in which biology was even more of a black box than it is currently.
The Lederbergs devised a simple experiment to test this idea. They grew bacteria on agar plates without the presence of an antibiotic that the strain was sensitive to. They then stamped this master plate onto a sterile piece of velveteen, so some of the cells adhered to the pile. This velveteen was then stamped onto a number of fresh plates containing the antibiotic the cells were known to be sensitive to. If the mutations conferring resistance happened before exposure to the antibiotic, resistant colonies would form in the same location on the fresh plates, because they would have been derived from a resistant ancestor on the master plate. Conversely, if the mutations were induced by the presence of the antibiotic, there would be no correlation in location of the resistant colonies from one plate to another. The results clearly showed that the locations where resistant colonies grew were consistent across the replica plates made from a given master plate, showing that the mutations responsible for the adaptation arose in an environment in which they would not have been expected to be advantageous. This paper also details the equivalent experiment involving bacterial resistance to a virus which infects the wild type--again, resistance crops up in the same locations repeatedly, indicating that it is derived from changes which occur before exposure to the virus.
This paper also outlines the use of sterile velvet for replica plating--a technique I myself have used repeatedly in the lab to screen for certain types of mutations and/or genetic engineering. In general, it's fairly easy to screen most traits in one direction--if you want to find which bacteria are resistant to a given antibiotic, you put the antibiotic in their growth medium, and anything that grows will resist it. Sometimes, though, you want to select for the cells which are sensitive to the antibiotic, or which require the addition of a certain chemical in order to grow, or the like. Replica plating provides an efficient way to screen hundreds of colonies for these types of changes--make a master plates in the permissive environment (without the antibiotic, with any possible required nutrient, etc), and make replica plates on both the permissive and the strict environment (when the antibiotic is present, when a given compound is missing, etc.). Look for colonies which grow in the permissive environment but which don't in the sensitive one. There you go. To be more sure of yourself, you'll generally repeatedly test that it has the property you're looking for, but the odds are pretty good that it does, and it's a lot faster than other means of finding such negative properties.
So, thank you, Drs. Lederberg. this paper of yours not only established the importance of mutation prior to exposure to an environmental challenge, but also outlined a handy lab technique I've made repeated and systematic use of in my own experiments.
Showing posts with label science. Show all posts
Showing posts with label science. Show all posts
Monday, July 14, 2008
Friday, August 17, 2007
Another take on test scores
Recent list work: #9, #94
I've spent much of today catching up on recent issues of Nature and Science, as I've not been reading them as much this summer as I should. So, this is old news, but I just came across it today.
For those with access to Science, a few letters appear in the June 22nd issue regarding a study from February advancing a claim that higher standardized test scores are a predictor in graduate student success, as measured by things such as publications, etc. The first of these is the one I think is the more insightful.
As the letter's authors (Manuel Lerdau and Christopher Avery) point out, the initial finding hypothesized the twin causal links: 1) greater aptitude --> higher test scores, and 2) greater aptitude --> increased probability of success. That's a potentially valid causal chain. On the other hand, they suggest that the causal chain might be more along the lines of higher test scores --> greater support (both financial and mentoring) --> greater probability of success. This also strikes me as potentially valid.
As the letter writers state, these two different causal chains lead to very different policy views. I think it would be interesting to try to disentangle the two effects. One way of doing so off the top of my head would be to look at departments where students are given essentially the same financial support and teaching duties regardless of whether they have fellowships or not. (For instance, Stanford's Department of Biological Sciences). Another would be to look at students who have the very high test scores but don't have fellowships for other reasons--perhaps by being non-citizens and therefore disqualified from national fellowships such as those through the NSF. It would also be interesting to look at students who have fellowships and thus don't need to teach, yet have lower standardized test scores than peers in their departments. There could be some difficult things to control for in these examples--for instance, students with low test scores who have fellowships most likely have significant undergraduate research experience, which might let them hit the ground running--but I think the general idea of studying these things is worth exploring.
I've spent much of today catching up on recent issues of Nature and Science, as I've not been reading them as much this summer as I should. So, this is old news, but I just came across it today.
For those with access to Science, a few letters appear in the June 22nd issue regarding a study from February advancing a claim that higher standardized test scores are a predictor in graduate student success, as measured by things such as publications, etc. The first of these is the one I think is the more insightful.
As the letter's authors (Manuel Lerdau and Christopher Avery) point out, the initial finding hypothesized the twin causal links: 1) greater aptitude --> higher test scores, and 2) greater aptitude --> increased probability of success. That's a potentially valid causal chain. On the other hand, they suggest that the causal chain might be more along the lines of higher test scores --> greater support (both financial and mentoring) --> greater probability of success. This also strikes me as potentially valid.
As the letter writers state, these two different causal chains lead to very different policy views. I think it would be interesting to try to disentangle the two effects. One way of doing so off the top of my head would be to look at departments where students are given essentially the same financial support and teaching duties regardless of whether they have fellowships or not. (For instance, Stanford's Department of Biological Sciences). Another would be to look at students who have the very high test scores but don't have fellowships for other reasons--perhaps by being non-citizens and therefore disqualified from national fellowships such as those through the NSF. It would also be interesting to look at students who have fellowships and thus don't need to teach, yet have lower standardized test scores than peers in their departments. There could be some difficult things to control for in these examples--for instance, students with low test scores who have fellowships most likely have significant undergraduate research experience, which might let them hit the ground running--but I think the general idea of studying these things is worth exploring.
Saturday, July 28, 2007
Annoyance at trolls
After reading some utterly revolting commentary on Brendan's site (note: revulsion is not at all due to Brendan, who has no part in the racist commentary. He merely takes free speech seriously, and held his nose while allowing awful trash to spew out of the mouths of trolls), I am once again struck by the ability for people to be misinformed on science and try to use it in defense of their ridiculous notions. There's a lot of flat-out incorrect information out there concerning the biology of race, and I just eventually decided that I should say something about it.
1) It is technically incorrect to argue that there is only one human race. For this one, I blame a lot of science fiction writers for referring to sentient aliens as alien races. This, I believe, has caused people to think that race means the same thing as species; I admit when I was younger I was under that impression as well. In reality, a biological use of the word race is akin to that of breed: it is a group of individuals sharing common physical characteristics which differentiate that group from other members of the greater population. To this extent, there are human races, as it is indeed possible for most people on sight to distinguish, for instance, someone whose ancestry 1,000 years ago trace primarily to Europe from one whose ancestors at that time lived primarily in Australia. How many human races there are is up for considerable debate, but there are physical characteristics which differentiate people whose ancestry lies primarily in different geographical regions.
2) The fact that we can distinguish primary racial background from individuals with relatively low levels of population admixture in their background does not mean that we can distinguish racial background based on blood samples. There are a small number of known biological characteristics which are significantly more common in individuals of one population or another, which allows for a greater probability of guessing "correctly", but these are still probabilities. For instance, beta thalassemias are a class of blood disorders characterized by mutations in the splice sites of the hemoglobin beta protein. These are much more common in areas of the world with malaria, and different versions of the disorder are more or less common in various regions. If you have a blood sample showing a beta thalassemia of one particular type, you can say that it's more likely to be from someone with ancestry in Greece than a random blood sample is, for example. We can also use markers on things inherited from just one parent--the mitochondria to establish the matriline, the Y-chromosome to establish the patriline--and therefore trace a small percentage of any individual's genetic legacy fairly accurately. But this is only true for a small fraction of your genetic background, and it remains important to point out that ~85% of human genetic diversity remains within populations, and only ~15% exists between populations (Rosenberg et al, Science 2002). At the genetic level, humans are remarkably not diverse.
3) That being said, it is indeed possible for forensic scientists to make a determination about some racial characteristics from skulls. Morphometric data from skulls of individuals with low degrees of genetic admixture have some degree of differentiation which has been attributed to natural selection, particularly in characteristic regarding breadth and depth of nose (for example, Roseman and Weaver, Am. J. Physical Anthropol. 2004). However, I will also say from personal experience having looked at casts of human skulls, to the untrained eye the only difference among anatomically modern human skulls visible without the use of calipers is that of the Inuit v. all others, due to a distinct difference in roundness of the skull.
4) All of the above is written primarily about those rare populations where many generations of ancestry can be traced to the same geographical region. Particularly in modern times, though throughout human history and prehistory, there have been waves of migration and conquest, with substantial genetic exchange brought about therein. One consequence of the slave trade was indeed a greater degree of mixing of genetic information from Europe and Africa, more within the Americas than in Europe or Africa themselves. People often forget that we in the US are in a country of immigrants, and one in which significant amounts of genetic mixing have been common for centuries. If you take a random genetic sequence from you and two other individuals in this country, one who shares your self-described race and one who doesn't, unless the most recent common ancestor is within the past few generations you are not more likely to group with the person of your race than the person from outside it.
The level of information and logical reasoning in the commentary is severely lacking, from people arguing multiple different points of view. As a few quick examples for those who don't feel like reading the tripe: Black people are the descendants of Cain, and the mark of Cain is his ugly dark skin, and Cain was born from the union of Eve and the Serpent so therefore isn't a descendant of Adam like all white people are (let's argue against that with, say, Genesis 1:4 "Adam lay with his wife Eve and she became pregnant and gave birth to Cain"). Greeks have a lot of Black blood in them, black women and mixed race children are inherently ugly (let's go with, say, the fact that the woman the Western world has held up as the ideal of beauty for centuries was a Greek woman by the name of Helen. This, incidentally, lends itself to the wonderful unit of beauty, the miliHelen: the level of beauty required to launch a single ship). Or we have the assertion that north Africans ruled Europe for 700 years (um, really? When? And who were they? The Moors held the Iberian penninsula for about 8 years, but the only major conquering of Europe which lasted any appreciable length of time was Rome conquering almost everything else, but last I checked Rome was in Europe, not Africa. Africa did conquer Europe when our own ancestors moved in and displaced the Neaderthals, but that's not history so much as prehistory). Other such drivel abounds, and none of it's really worth my time debunking. But, as is my wont, I will go after some of the misstatements, lies, and misuse of science. Race is a complicated matter in both biology and anthropology. If you're going to try to make assertions about what these disciplines have to say on the matter, spend the time to actually read about it in reputable journals first.
1) It is technically incorrect to argue that there is only one human race. For this one, I blame a lot of science fiction writers for referring to sentient aliens as alien races. This, I believe, has caused people to think that race means the same thing as species; I admit when I was younger I was under that impression as well. In reality, a biological use of the word race is akin to that of breed: it is a group of individuals sharing common physical characteristics which differentiate that group from other members of the greater population. To this extent, there are human races, as it is indeed possible for most people on sight to distinguish, for instance, someone whose ancestry 1,000 years ago trace primarily to Europe from one whose ancestors at that time lived primarily in Australia. How many human races there are is up for considerable debate, but there are physical characteristics which differentiate people whose ancestry lies primarily in different geographical regions.
2) The fact that we can distinguish primary racial background from individuals with relatively low levels of population admixture in their background does not mean that we can distinguish racial background based on blood samples. There are a small number of known biological characteristics which are significantly more common in individuals of one population or another, which allows for a greater probability of guessing "correctly", but these are still probabilities. For instance, beta thalassemias are a class of blood disorders characterized by mutations in the splice sites of the hemoglobin beta protein. These are much more common in areas of the world with malaria, and different versions of the disorder are more or less common in various regions. If you have a blood sample showing a beta thalassemia of one particular type, you can say that it's more likely to be from someone with ancestry in Greece than a random blood sample is, for example. We can also use markers on things inherited from just one parent--the mitochondria to establish the matriline, the Y-chromosome to establish the patriline--and therefore trace a small percentage of any individual's genetic legacy fairly accurately. But this is only true for a small fraction of your genetic background, and it remains important to point out that ~85% of human genetic diversity remains within populations, and only ~15% exists between populations (Rosenberg et al, Science 2002). At the genetic level, humans are remarkably not diverse.
3) That being said, it is indeed possible for forensic scientists to make a determination about some racial characteristics from skulls. Morphometric data from skulls of individuals with low degrees of genetic admixture have some degree of differentiation which has been attributed to natural selection, particularly in characteristic regarding breadth and depth of nose (for example, Roseman and Weaver, Am. J. Physical Anthropol. 2004). However, I will also say from personal experience having looked at casts of human skulls, to the untrained eye the only difference among anatomically modern human skulls visible without the use of calipers is that of the Inuit v. all others, due to a distinct difference in roundness of the skull.
4) All of the above is written primarily about those rare populations where many generations of ancestry can be traced to the same geographical region. Particularly in modern times, though throughout human history and prehistory, there have been waves of migration and conquest, with substantial genetic exchange brought about therein. One consequence of the slave trade was indeed a greater degree of mixing of genetic information from Europe and Africa, more within the Americas than in Europe or Africa themselves. People often forget that we in the US are in a country of immigrants, and one in which significant amounts of genetic mixing have been common for centuries. If you take a random genetic sequence from you and two other individuals in this country, one who shares your self-described race and one who doesn't, unless the most recent common ancestor is within the past few generations you are not more likely to group with the person of your race than the person from outside it.
The level of information and logical reasoning in the commentary is severely lacking, from people arguing multiple different points of view. As a few quick examples for those who don't feel like reading the tripe: Black people are the descendants of Cain, and the mark of Cain is his ugly dark skin, and Cain was born from the union of Eve and the Serpent so therefore isn't a descendant of Adam like all white people are (let's argue against that with, say, Genesis 1:4 "Adam lay with his wife Eve and she became pregnant and gave birth to Cain"). Greeks have a lot of Black blood in them, black women and mixed race children are inherently ugly (let's go with, say, the fact that the woman the Western world has held up as the ideal of beauty for centuries was a Greek woman by the name of Helen. This, incidentally, lends itself to the wonderful unit of beauty, the miliHelen: the level of beauty required to launch a single ship). Or we have the assertion that north Africans ruled Europe for 700 years (um, really? When? And who were they? The Moors held the Iberian penninsula for about 8 years, but the only major conquering of Europe which lasted any appreciable length of time was Rome conquering almost everything else, but last I checked Rome was in Europe, not Africa. Africa did conquer Europe when our own ancestors moved in and displaced the Neaderthals, but that's not history so much as prehistory). Other such drivel abounds, and none of it's really worth my time debunking. But, as is my wont, I will go after some of the misstatements, lies, and misuse of science. Race is a complicated matter in both biology and anthropology. If you're going to try to make assertions about what these disciplines have to say on the matter, spend the time to actually read about it in reputable journals first.
Tuesday, May 8, 2007
Random annoyance
I am still alive, just massively slackerly on the blog. For much of the past month, I can claim as an excuse the stats class that did its best to eat my life, in which I somehow managed a 4.0 despite not really caring about my grade nor feeling like I had mastered the subject matter. I guess old habits die hard. Every time I've taken a course pass/fail, I've ended up with one of the (if not always the overall) highest grades in the class. This class I wasn't taking pass/fail officially, but in my mental state for the term, a 3.0 was all I cared about. However, I do have an explanation: I only take classes pass/fail when I think they are complex and confusing. And I don't do well at not understanding things, so I tend to freak out and actually put in effort when I don't get what's going on. Therefore, it's not that the pass/fail grading scheme is causal to my doing well, but rather that there's a strong correlation between classes which intimidate me enough to take pass/fail, and courses in which I'll be scared into putting in substantial effort.
As for the random annoyance, I had two negative controls from yesterday's work. Same growth media in the two different types of containers I used. One of them was contaminated today; the other was not. And the one that was contaminated having to be restarted throws off my schedule for about a week, while the other one (had it been contaminated) would have had virtually no impact on my schedule. Grr.
As for the random annoyance, I had two negative controls from yesterday's work. Same growth media in the two different types of containers I used. One of them was contaminated today; the other was not. And the one that was contaminated having to be restarted throws off my schedule for about a week, while the other one (had it been contaminated) would have had virtually no impact on my schedule. Grr.
Monday, February 12, 2007
The study of the paranormal
Furthering today's theme of posting about science (sort of), another piece from the NYTimes this weekend concerned the fate of a Princeton lab which has, for decades, attempted to study psychic abilities. Basically, the worker in this lab tried to see if human thoughts could alter what would otherwise be random events--random number generation, physical movements, etc.
In what will probably surprise anyone who met me in college or later, I at one time assumed I'd take a course in parapsychology. I've always believed that most people claiming psychic powers were frauds, but I figured there might be some legitimate basis to telepathy in particular. Just because I thought most of those claiming the abilities were frauds didn't mean I was convinced the abilities didn't exist.
In reality, I think most of the research from this lab is suspect. As Michael Shermer points out in Why People Believe Weird Things, you should generally be skeptical of things which purport to show only very tiny effect sizes. And the effect sizes claimed by this lab are indeed tiny. "Analyzing data from such trials, the PEAR team concluded that people could alter the behavior of these machines very slightly, changing about 2 or 3 flips out of 10,000." When effect sizes are that small, they're extremely unlikely to be meaningful.
But, at the same time, I'm annoyed by things like "Prominent research journals declined to accept papers from PEAR. One editor famously told Dr. Jahn that he would consider a paper “if you can telepathically communicate it to me.”" How annoyed I am depends on how you interpret it. If it's a statement that the papers were rejected outright because of who it was submitting them, without looking at the evidence, that's a bad thing. If it's that the papers were declined because the editors didn't think the authors had proved their claims, that's something else.
However, it should be pointed out, it's not fair to sit back and blithely condemn journals for not considering all submissions. Journals are deluged with huge numbers of manuscripts. It takes time, energy, and expense to review them thoroughly. It is therefore reasonable for many journals to conduct a form of academic triage--only thoroughly review those papers which are unlikely to have serious logical or methodological flaws and which claim interesting results in the abstract. Still, there are so many journals out there that it seems unlikely that the lab simply couldn't find a journal willing to give a thorough review to their submissions, and that's why they had to found there own. Color me skeptical when a group publishes only in a journal run by the members of the group.
In what will probably surprise anyone who met me in college or later, I at one time assumed I'd take a course in parapsychology. I've always believed that most people claiming psychic powers were frauds, but I figured there might be some legitimate basis to telepathy in particular. Just because I thought most of those claiming the abilities were frauds didn't mean I was convinced the abilities didn't exist.
In reality, I think most of the research from this lab is suspect. As Michael Shermer points out in Why People Believe Weird Things, you should generally be skeptical of things which purport to show only very tiny effect sizes. And the effect sizes claimed by this lab are indeed tiny. "Analyzing data from such trials, the PEAR team concluded that people could alter the behavior of these machines very slightly, changing about 2 or 3 flips out of 10,000." When effect sizes are that small, they're extremely unlikely to be meaningful.
But, at the same time, I'm annoyed by things like "Prominent research journals declined to accept papers from PEAR. One editor famously told Dr. Jahn that he would consider a paper “if you can telepathically communicate it to me.”" How annoyed I am depends on how you interpret it. If it's a statement that the papers were rejected outright because of who it was submitting them, without looking at the evidence, that's a bad thing. If it's that the papers were declined because the editors didn't think the authors had proved their claims, that's something else.
However, it should be pointed out, it's not fair to sit back and blithely condemn journals for not considering all submissions. Journals are deluged with huge numbers of manuscripts. It takes time, energy, and expense to review them thoroughly. It is therefore reasonable for many journals to conduct a form of academic triage--only thoroughly review those papers which are unlikely to have serious logical or methodological flaws and which claim interesting results in the abstract. Still, there are so many journals out there that it seems unlikely that the lab simply couldn't find a journal willing to give a thorough review to their submissions, and that's why they had to found there own. Color me skeptical when a group publishes only in a journal run by the members of the group.
Litmus ideology and science
I came across an interesting article in the NYTimes today. In summary, it's about a man who got a PhD in geoscience, writing a dissertation about the spread of mosasaurs, which went extinct 65 million years ago. The man also happens to be a young Earth creationist, believing that the Earth is less than 10,000 years old, and was created according to accounting in Genesis.
I have a few reactions to this article, which are probably not well organized at the moment, but which I feel like writing about right now anyway.
One, I find it absurd that people feel he shouldn't have gotten the degree simply because he doesn't completely believe it. (For example: "His creationism aroused “some concern by faculty members there, and disagreements,” he recalled, and there were those who argued that his religious beliefs should bar him from earning an advanced degree in paleontology.") If his work is a valid contribution to the field, then whether he disagrees with his own work due to religious reasons is irrelevant. Universities should not be in the job of making students pass an ideological litmus test. Educating about the science of evolution is not brainwashing. As long as the students understand the arguments and predictions therein, that's all that the university can really demand that they know of a given theory. Greater demands can be placed on the details of how their dissertation intersects with a theory, but disputing a theory is not sufficient cause to refuse a degree.
At the same time, I do draw a distinction between that and another related topic brought up in another paragraph:
What sort of federal investigation would be at all reasonable? Letters of recommendation are personal, subjective evaluations of students. Any professor can hold any standard (s)he wants to write such a letter. If one of my professors felt that I'd be unqualified for graduate work because I'm a white male and there are too many of those in grad school already, that's his/her right. I may disagree, but I have no federal right to a letter of recommendation.
On the other hand, I do find at least one of the statements attributed to this man to be dishonest. ("And though his dissertation repeatedly described events as occurring tens of millions of years ago, Dr. Ross added, “I did not imply or deny any endorsement of the dates.”") Bull. It's in your dissertation thesis. If you don't refute it there, or at the very least clearly distance yourself from it by saying things like "Smith et al argue that these fossils are from..." or "One interpretation is that...", you are indeed implying endorsement of the statement.
I know that, long-term, I will have students in my evolution courses who disagree with evolution. For the most part, I must admit that I believe this is caused by some combination of misinformation about the reality of the biological arguments about evolution and a certain degree of doublethink on the part of the students. But it's not my place to dictate what they believe. My job is to teach the information and evaluate their understanding of it and ability to apply it. If they can do that but choose not to believe it--because they have alternate beliefs, or put less faith in scientific methodology than they do in appeals to other authorities, that in no way makes them less deserving of the mark they've earned.
I have a few reactions to this article, which are probably not well organized at the moment, but which I feel like writing about right now anyway.
One, I find it absurd that people feel he shouldn't have gotten the degree simply because he doesn't completely believe it. (For example: "His creationism aroused “some concern by faculty members there, and disagreements,” he recalled, and there were those who argued that his religious beliefs should bar him from earning an advanced degree in paleontology.") If his work is a valid contribution to the field, then whether he disagrees with his own work due to religious reasons is irrelevant. Universities should not be in the job of making students pass an ideological litmus test. Educating about the science of evolution is not brainwashing. As long as the students understand the arguments and predictions therein, that's all that the university can really demand that they know of a given theory. Greater demands can be placed on the details of how their dissertation intersects with a theory, but disputing a theory is not sufficient cause to refuse a degree.
At the same time, I do draw a distinction between that and another related topic brought up in another paragraph:
Michael L. Dini, a professor of biology education at Texas Tech University, goes even further. In 2003, he was threatened with a federal investigation when students complained that he would not write letters of recommendation for graduate study for anyone who would not offer “a scientific answer” to questions about how the human species originated.
What sort of federal investigation would be at all reasonable? Letters of recommendation are personal, subjective evaluations of students. Any professor can hold any standard (s)he wants to write such a letter. If one of my professors felt that I'd be unqualified for graduate work because I'm a white male and there are too many of those in grad school already, that's his/her right. I may disagree, but I have no federal right to a letter of recommendation.
On the other hand, I do find at least one of the statements attributed to this man to be dishonest. ("And though his dissertation repeatedly described events as occurring tens of millions of years ago, Dr. Ross added, “I did not imply or deny any endorsement of the dates.”") Bull. It's in your dissertation thesis. If you don't refute it there, or at the very least clearly distance yourself from it by saying things like "Smith et al argue that these fossils are from..." or "One interpretation is that...", you are indeed implying endorsement of the statement.
I know that, long-term, I will have students in my evolution courses who disagree with evolution. For the most part, I must admit that I believe this is caused by some combination of misinformation about the reality of the biological arguments about evolution and a certain degree of doublethink on the part of the students. But it's not my place to dictate what they believe. My job is to teach the information and evaluate their understanding of it and ability to apply it. If they can do that but choose not to believe it--because they have alternate beliefs, or put less faith in scientific methodology than they do in appeals to other authorities, that in no way makes them less deserving of the mark they've earned.
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