Siliceous and Delicious

Yesterday, while I wasn’t on top of my game and didn’t feel like I produced much, was a bit of a turning point—I finally finished my list of characters! Huzzah! It consists of a list of 130 characters, each with anywhere between two and eight character states. Some (but not many) of the characters have explanatory notes and/or images; I intend to add such notes and images to most or all of the characters as I start making passes through them for each of the taxa.

I didn’t send them out for review yesterday—I wanted first to read through them once to check for consistency, and craft a short introduction to explain the philosophy I’ve taken in putting them together. Kate got sick in the afternoon and I aborted work early to go and pick her up so she wouldn’t have to trudge through the freezing rain. This morning, the distractions continued—I had to gather up and mail the last remaining (I hope) documents for the immigration case. What a time-consuming pain in the backside that whole experience has been.

Reviewed the characters, made a couple of small changes. In some cases I’m still not sure if this isn’t too fine-grained an approach. Maybe I’ve wasted my time in going into so much detail. On the other hand, my last attempt at doing this was criticized for its focus on taxonomically crucial characters, so I have tried to respond in the best way I can by using characters that describe frustule morphology as completely as possible. I tried to explain this in my email to Andy, Jacques, and Charles, and sent it off. Somewhat of a relief—though I await their responses (Charles’ especially) with a fair bit of trepidation. On the other hand, I don’t even care that much anymore. The worst that could happen is that Charles waxes eloquent about how stupid the whole exercise is, in which case I shall smile and nod (or whatever the email equivalent is) and continue to do what I planned to do anyway, because I know it’ll be reasonably interesting to three or four people, and I need to get it done so I can graduate. More likely in any case is that Charles won’t reply at all, and I’ll end up taking his silence as implicit approval, and move on. Safe in the knowledge (or hope) that this will be some sort of insurance against him acting up before my defense and refusing to let me graduate because he thinks my work is garbage.

I also emailed Wiebe Kooistra, as per Andy’s suggestion, to ask if he would look over my characters as well. He emailed back within a couple of hours with two names of more appropriate reviewers—one of whom, David Mann, I emailed with the same message I’d sent Kooistra. He’s one of the authors of the Diatom Bible (“The Diatoms” by Round et al.) I’ve been using, so if he’s not the guy, I don’t know who is.

Feels good to get something done, in spite of the worries that it might all be rubbish. The task now is not to lose momentum, but to press ahead with the next step. What is the next step? I consider my possibilities: throwing myself into the mathematical morphospace (with Sébastien), or getting started on the radiolarian lineage project. My feeling is that I ought to do the mathematical morphospace, because I’m afraid it’ll wither and die if I don’t pay it attention, but that I want to do the radiolarian project, because it has the same promise of unimpressive do-ability as the character-based morphospace. I know that if I sit down and work at it, something will come of it. The mathematical morphospace is quite a different beast, and I’m scared of it—scared that I’ll throw three weeks, two months, goodness knows how much time at it, and get nothing out of it.

No post yesterday, and not much progress. Had been hoping to hear back from Sébastien and be able to talk to him about how to proceed, seeing as I’m pretty well stuck with the shape extraction algorithm. Thankfully, I had DSA to help me step back half an inch and see there’s another thing I can be productively working on in the meantime, namely consolidating the character list.

Now that I’m working on a fairly detailed generative (?) morphospace for the outline, I’m noticing that I’ll probably need fewer characters to describe the outline shape. For example, I won’t need a descriptive discrete character for presence/absence of a central swelling. When it comes to the apex shape, I’m less sure. Will I be able to capture the difference between a rostrate and sub-rostrate apex with the Fourier modes? I think so.

But even leaving this out, rolling the notes I’ve assembled on the various characters together into a coherent character set is tricky. How to integrate a long list of descriptive terms and phrases lumped under “valve face topography” with transverse vs. longitudinal sulci, and the canonical list of terms for the “girdle view outline” shape?

Got stuck and overcome by a deep desire not to work. Not sure why. Frustrating.

Started the day with a meeting with Jacques. He started out quite pessimistic about the sonication project, highlighting the sense he’d gotten from the SEM images I sent him that the frustules were deforming in a ductile rather than a brittle fashion. However, since there were a lot of small fragments in the sonicated samples I looked at, in all likelihood brittle failure did occur (it’s unlikely they were all rubble before I started sonicating them), suggesting a glimmer of hope that something may come of it. The suggestion was to try again, but with less or no sonication at all. To resuspend the cells after centrifuging, Jacques suggested using a shaker table, which we promptly procured by “borrowing” one from a neighboring lab. He didn’t have the sulfuric acid, oxalic acid, and potassium permanganate that a recipe for cleaning diatoms (by Hasle and Fryxell, 1970) suggested, so I’ll have to find those elsewhere (Colleen’s lab, maybe).

With a productive conversation under my belt to start the day, I thought I’d move on to the diatom morphospace project, as I had promised myself yesterday. But, it was not to happen—distractions here, distractions there, an unavoidable trip to lunch to celebrate Ben Gill’s paper finally making into Nature, family emails and phone calls, and somehow it was all over before it even started.

Back yesterday morning after a very welcome break in The Hague, Düsseldorf, and Amsterdam. Spent the morning catching up on e-mails, and booking my flight to DC for next week to go and pick up samples from the Smithsonian for the radiolarian by-lineage study. Though I started strong in the morning, jet lag soon caught up with me, and I wasted most of the afternoon away just trying to stay awake. It might have been more productive to stop work and go for a walk in the beautiful autumn sun.

I need to think about a strategy for the coming weeks. It’s going to be a fairly busy time, what with Maria coming to visit, and I am going to need to prioritize. A good time to review where I am with each of my projects (oh, how I wish I had Tony’s whiteboard back now!):

2A: Pre-Cenozoic Rads—Project sleeping. Can’t be a priority right now, because it’s essentially got a daft input:output ratio (way lots of work for dubious payoff).

2B: Rad lineages—Finally approaching start time on this one. Flying to DC next Wednesday to pick up samples for five of the six chosen lineages from the MRC at the Smithsonian based on the list I made over the summer. I am very hopeful the slides I picked will actually have the taxa I need in them. I could, of course, spend much longer at the MRC and actually check the slides before I select them (this would be the smart way to do it), but since I had assumed I’d be able to just request the slides and have them shipped to me, I had already started down the “pick samples and hope” path. Worst case scenario is that I find the samples don’t have what I need in them, and I go back for another day or two to get more. Not the end of the world, and probably more efficient than going through all the samples there only to go through them again once I get here.

The sixth lineage, Lophocyrtis, is still waiting to have samples selected. I hadn’t found it easily possible to get samples for these out of the MRC/Neptune combo, and decided to write Annika Sanfilippo for help. It turned out she has many samples from this lineage, which she described and defined over several decades. She has offered to send me whatever samples I want, but I haven’t been able to figure out exactly what samples she has, nor what taxa are found in them. The lineage is complicated and has lots of splits and branches in it. Annika also sent a stack of her notes on one of the descendant lineages of Lophocyrtis, Cyclampterium, by mail. I need to go through this and figure out which samples I want from her for a first-pass study of the lineage.

3: Diatom morphospace—this project is tantalizingly close, and I feel frustrated not to be making more progress on it, because the promise of getting it out the door is palpable. The next steps are quite clear, finish going through the stack of papers from the Farlow, then synthesize the morphological notes I’ve been taking into a master list of characters and associated character states. The challenge there is going to be to find a good way of describing the gross morphologies, e.g. valve outline shape, and dealing with the difference in sets of characters between raphid/pennates and centrics. Once that’s done, I can send it off to Wiebe Kooistra for review. Then, after making whatever adjustments I need from Wiebe’s comments, I can send it to Charles for review, and following further adjustments, plug and chug on coding the characters for each of the genera in Neptune.

4A: Extant diatom FIB—this project is essentially sleeping, too, since the diatoms I ordered from the CCMP came back all crappily silicified.

4B: Fossil diatom FIB—just sent an email to Nicholas to set up the next overnight FIB sessions. I’m not doing anymore unassisted sessions, since I’m sick of wasting my time doing runs that lead to nothing because there’s some technical glitch or another that I can’t fix myself.

5: Diatom sonication—got the diatoms, sonicated them, put them under the SEM, they are very lightly silicified and very zapped-to-bits. Next step is to try cleaning them again without destroying them as much (i.e. less sonication). Don’t know how to do this, so need talk to Jacques about it. That’s the next immediate step. The medium term decision is how to go ahead, whether it’s possible to work with this material, or to re-order more material, or to try to culture this myself (I’m not really interested in that option as much, it’d be a lot of work, although at least now there’s a cleaner lab without Dave’s meddling to work with). I suppose another option is to travel up to Canada again and do the culturing work with Zoe. Apart from her agreement, this would require a pretty substantial time investment in the cold dark depths of Canada, which I’m not excited about.

6: Diatom diversity/E-O—kind of unexcited about this project at the moment. I suppose the next step is to get the Alroy-style subsampling working, though I’m now hoping to implement in a slightly different way, because I think his way is too specific for PBDB, not necessarily appropriate for Neptune given what I’ve learned from reviewing Dave’s manuscript about the Neptune data. Ideally the right way to go about this will be to apply some Dave-style pacman/hats-for-rats type data filter, then a Neptune-appropriate subsampling based on % coverage (i.e. SQ subsampling). The next step here is to do a bit of thinking and planning, and probably ideally talking to Charles/writing up what I’ve learned from Dave’s paper and outlining my strategy. This is going to take some time and I’m hesitant to sink time into it when I’m so much closer to getting somewhere with other projects.

So much, then, for where I am. Where to go next, where to focus my energy, and how to do it, is the question. I went ahead and booked FIB time with Nicholas for the overnight slot from Monday-Tuesday. To be realistic, the time I have available before Maria gets here next Friday evening is just over four days. Friday afternoon is lab meeting at MIT, which will make for a short day. Monday afternoon I will be setting up the FIB overnight run, so that will be a short day. Wednesday I’ll fly out to DC at 6:30 am and won’t return until late at night. That leaves Thursday and Friday. So four days and a bit.

I really feel stuck deciding between these two. In a conversation with Jc I learned that she does most of her work in bigger chunks—rather than units of hours or days, she switches projects weeks at a time. This suddenly struck me as a very wise thing to do; a lot of my stress I think comes from trying to decide what to do next, and once I do, a lot of energy sinks into switching my brain back and forth from one project to another. As important as I think getting the samples ordered from Annika is, I think my primary need right now (for emotional reasons if nothing else) is to make progress, and the best promise for making progress is with the morphospace project. So as much as it pains me to leave the other projects aside for the moment, especially since they all feel pressing at the moment, to some degree or another, that’s where I think I should start focussing now.

Tomorrow.

Although that’s kind of what I felt like telling him, unlike HAL-9000, I do still need Dave. So I finally buckled down this morning to step through the rest of his manuscript, hunting down typos and noting what constructive things I can say about each section.

I had left off the last time at the section “Preservation at the species level”. In his table of % preservation of extant species, he gives diatoms only a <50% percent score, but gives the total extant diversity as 1,500. While I have no doubt that there are at least that many diatom species today, I’m not convinced that there are anywhere near that many that are commonly found as pelagic, planktonic species. Much of the extant diatom diversity (which far exceeds 1,500) is terrestrial/lacustrine or benthic/epiphytic marine, and is sampled in the Souria survey as tychoplankton. I chased up the Souria, 1991 species to see where that number comes from. Indeed, between 37 and 44% (depending on whether you choose the low or high end of their range estimate) of the diatom diversity reported consists of pennates—which are mostly benthic. I think if you were to include only those species that are, like radiolarians, exclusively marine and planktonic, the % of preservation would be far higher. It would also be nice to have the number of preserved fossil species in the table (not just the %age), and a source reference for that number, cited in the table legend. Well, I just checked the Kooistra chapter in Falkowski & Knoll, and he cites numbers between 5,000 and 10,000 for the diversity of strictly marine planktonic diatoms. Oops. Well, scratch that, then.

Much of the rest of the section is OK, although there’s a paragraph on page 7 I have a bit of a hard time with. I don’t think I’ll comment on it, but Dave makes the point that even though preservation is so good, it’s possible that there were times when very ill-preservable species of radiolarians evolved, that left no record. Sure, it’s possible, but so what—it’s also possible that the Earth was invaded time and again over its history by purple alien cloud-people who left no footprints and no traces of their influence. Sure, it’s possible.

He also makes the point that there are ‘significant gaps’ because some regions, such as the gyres, don’t leave much of a microfossil record at all. This is true, but again it seems like peanuts compared with the sort of comparatively appalling preservation characteristic of invertebrate fossils on the shelves.

When Dave talks about hiatuses, again, he makes the deep sea record seem worse in comparison to the shelf record, in a way I’m not sure is fair—because he suggests there are no changes in lithology to suggest a hiatus has taken place. My sense is that changes in lithology don’t necessarily help you in shelf sections—sometimes they might represent very little time, and sometimes there can be consistent lithology over many millions of years. I’m not sure the problems of recognizing the partitioning of time in rocks are really meaningfully different in deep and shallow sediments.

Fortunately Dave ends the section on quite a positive note; perhaps I didn’t quite appreciate this on first reading. He says that in spite of all of this, the record is really good—species level evolution for entire clades for most of the biogeographic provinces over the past 100 million years.

Unfortunately, he then launches into a diatribe about how poorly this record is recovered and documented. This is the next section, “Recovery of Deep-sea Fossil Material”. This section begins with a description of piston-coring, and its fantastic coverage, but the admittedly damning limitation of short timescale. Moving on to deep-sea drilling material, he duly acknowledges the staggering number of fossils already available for study (at least 10^15 specimens, a million times more than all the world’s natural history museums combined), and the fact that most of these come with coeval paleoenvironmental data. Surprisingly (for me, given what I remembered from my first reading of the paper) he also ends this section on a positive note, namely that the record is nearly complete at the species level, given that the MRC holds more than 100 samples per million years for most of the Cenozoic.

In the next section, “IRAT—Imperfections in the Existing Dataset”, he explains why the data generated from these samples is less than complete, and why it’s a problem to use them for paleobio research. “Incomplete Data” outlines a problem with how species are recorded on a slide. Rather than the ideal model, in which the paleontologist records the taxonomic identity of a certain number of specimens, and then moves on to the next slide, thereby obtaining a random and unbiased subsample of the sample in hand, the situation is usually as follows. The paleontologist has a list of taxa that is as short as it can usefully be, and he records presence/absence (or abundance) of those taxa in order to determine the age of the sample.

But on top of this, the paleontologist often records some additional taxa, which do conform to the random sampling. Crucially, he states that “the differences in the average reported diversity per sample/study simply reflect the average practical size of a taxonomic list, and do not have a necessary relationship to actual real sample diversity”. Now this seems to be the key sentence. Does this mean each study has a different taxonomic list, and that’s what determines list length, more so than underlying diversity? If so, this should be easy to test (and I think Dave should do this if he wants to back up his argument): what publication a sample is from should be a better predictor of list length than what time it’s from. So, if the Neptune database has publication information (which I hope it does), you should be able to parse the data by time bins vs. by publication, and see if the variability is better described by what time bin samples are in, or by what publication they’re from. This could be compared by Akaike weights, for example.

The next paragraph—on page 11—is really quite confusing, and stands at the heart of the part of this paper that affects what I’ve been thinking about and doing with diatom diversity. Dave states that most data is collected by his “model C”, so the model where paleontologists record the presence/absence of taxa on a list, plus whatever other taxa they fancy. He states that this leads to a correlation between sample availability and total diversity, but not because of the reason we might think (i.e., going up a collector curve)—but rather, because sample availability is correlated with taxonomic effort. I think what he means here is that sections with more samples available have “model B” taxonomic lists that are longer than sections with few samples. It seems to me, though, that this reduces down to the same thing as collector curves, albeit via the detour of constructing a list: the more diverse-seeming assemblages seem thus because they have longer “model B” taxonomic lists, not because they’ve had more random samples taken, but the reason they have longer taxonomic lists is because there is more “sample availability”, as Dave puts it, which I think means… they have been more extensively—randomly—sampled.

In the next paragraph, he rallies support from a figure (figure 8) that I just don’t understand. The point he’s trying to make is that species are more rarely reported than they should be, I think; what he shows is a histogram of the number of samples from which a radiolarian taxon is reported; 100+ taxa show up in only 1-5 samples, and 40+% of taxa show up in 25 samples or fewer. Besides the fact that the plot is confusing (not clear what the inset plot is, vs. the main plot, nor what the total number of samples is) and the calculation in the figure caption is impossible to follow, I’m not sure this addresses the same point as the preceding paragraph. That paragraph was trying to say that subsampling exercises wouldn’t work because many, or most, of the taxa in the database will be from “model B” lists of stratigraphic marker species. Apart from the fact that this might not be true (see below), the point explored with figure 8 is different.

Is it true that “model C” makes subsampling impossible? I think Dave might have his answer backwards, actually. If the “model B” list is consistent over time (and I’m not sure what Dave’s stance is on that—he seems to want it both ways at the beginning of this section), then you might actually be making a much fairer comparison if you are subsampling by lists, because each list you pull will be comparing apples to apples in its “model B” component. In addition it provides its “model A” component, but that should be subject to the same qualifying properties of random sampling as sanctioned by Dave in the beginning of the section, so it should behave well under subsampling. So, aren’t we actually improving things in this way?

Of course, if lists are different depending on what time interval we’re looking at, then I think the “model C” argument just breaks down to a “model A” scenario, more or less.

The main point here, though, is that this does not distinguish the microfossil record in any way from the rest of the fossil record—dominated by shelf invertebrates—as recorded in PBDB. That record is also a combination of biostratigraphic occurrence data of a limited, and commonly represented, stratigraphically informative species, and a more or less random sampling of other taxa. How does that make the microfossil any worse?

Moving on, the section “Reworking” opens with the claim that reworking affects only the microfossil record, a claim I think can hardly be considered true. I don’t have any great references at hand, but can offer one (sight unseen, thanks to a lapsed subscription to Lethaia, cheers Harvard): Fürsich, F.T. 1978. The influence of faunal condensation and mixing on the preservation of fossil benthic communities. Lethaia, Volume 11, Issue 3, pages 243–250. Also Kidwell, S.M., 1998, Time-averaging in the marine fossil record: overview of strategies and uncertainties: Geobios, v. 30, p. 977– 995. Kidwell, S.M., and Bosence, D.W.J., 1991, Taphonomy and time averaging of marine shelly faunas: in Allison, P.A., and Briggs, D.E.G., eds., Taphonomy: Releasing the Data Locked in the Fossil Record: Plenum Press, New York, p. 115–209. Recent study: DeFrancesco, C. and Hassan, G.S. 2008. PALAIOS; v. 23; no. 1; p. 14-23.

And again, these issues are all the same issues that befall the macrofossil record, too—I don’t think an obviously reworked specimen will be reported by a trilobite worker as occurring in the formation in which it was found.

The first sentence of the “Age Model Problems” sentence really says it all—they’re way better for the marine microfossil record than for any other record we have. And that should be the focus of the paper, not all the things that are wrong with it! In diversity studies, a 1-my error is not a problem if we use 2-my bins. Also, this error is unbiased—and this is a critical point—so for macroevolutionary studies, it really shouldn’t matter. As long as it affects everything equally, and more or less evenly throughout time, we should be golden as long as the signal we’re trying to see is strong enough.

The same “but it’s even worse in the rest of the fossil record” argument can be brought against the “Taxonomy” section, which says because there’s convergence and some morphospecies overlap through time, but this has got to be a pretty minor problem and should only cause ranges to extend very slightly.

“Reworking, Age Model Errors and Macroevolutionary Metrics”. Dave shows his calculations (or their result) that suggest 5% of radiolarian LADs in Neptune are off, and 3% of FADs. He adds it up to a total error of 8% of all occurrences being outside the true range of the species. This leaves the apparent ranges of many taxa extended beyond their true ranges, which is a big difference to most of the rest of paleontology, where the opposite is the case (this is actually a really good point, I think). But because taxa are rare, Dave proposes using range-through; the problem then becomes the artificial range extension and how to deal with it.

I think it might be worth piping up here and putting in a word for Alroy and his distaste for range-through, because of the ugly edge effects it causes. But to illustrate the downfalls of range-through, Dave does something really sketchy here that bothers me a lot. He takes a 1 my time bin for forams in Neptune, and compares what’s found there to what’s supposed to be there based on the biostratigraphic framework.

Bumbled in rather closer to lunchtime than the morning today, but found that my harvested culture had finally arrived from the CCMP. I set to work immediately and spent the remainder of the morning bustling around—finding somewhere to store the frozen samples (Dave’s lab has a new freezer in which they found a home), finding a way to dispose of the dry ice (Ann’s lab found a use for it), and so forth. In the afternoon, set out on a mission to start using the sonicator—a mission, like all grad school missions it seems, that was far more odyssean than I could have imagined. Not only did I clean out a nook in one of their back rooms to have a space to use the sonicator, then move the hulk of a machine from the lab to that space; not only did I subsequently move the machine back to the lab after a grad student complained that the thing would be too noisy in the room next to her office (understandably enough of course), but I also had to settle on Friday morning as the first available time to be trained to use it. So, it looks like this project’s on hold for the rest of the week.

Of course, I’d have to wait anyway, since (as I found out) there isn’t any of the particular detergent (“RBS-35”) mentioned in the Crawford paper whose methods I am trying to follow available around these parts. And since this means putting in a VWR order with Diane (which I promptly did, after searching around in the Knoll and Pearson labs), it may be weeks before I see the stuff.

I had to cut the day short to answer one call for departmental community service I couldn’t turn down—Tom had asked me to come to his quals practice talk, feedback which I recall appreciating tremendously, so I had to return the favor (karmically speaking).

So, I didn’t get to writing the comments for Dave’s manuscript—and I don’t hold out too much hope for it tonight either. It feels like crap not having done it, but on the other hand, I really, really don’t feel like doing it. I know it’s awful, but I just can’t seem to help myself!

Decided to take it easier today. Jogged in for an early morning squash game, and trundled to work later than usual.

Didn’t really feel like going back to either the review of Dave’s paper, which really got me down yesterday, or tinkering with R, which I wasn’t enjoying as much as usual, but instead felt the urge to finish the task I’d been making the most progress on last week—the morphospace. There’s a whole stack of papers next to my desk now, just waiting to be turned into characters for the morphospace, and that’s what I want to be doing right now.

Dug up the remaining references from the Cabot science library (one was not there—a Hungarian journal for which the subscription seems to have lapsed before the issue I need was published) and made a trip to the Farlow for another. That one turned out to be a fantastic resource I wish I could have had at the beginning of this morphospace exercise, though I’m grateful at least to have it now. It’s a proposal for a standardized terminology for describing diatom morphology—including a bunch of illustrations, and a glossary for the French, German, and Latin equivalents of the terms used. That would have come in mighty handy in understanding some of those genus descriptions, but it’s also going to be of tremendous help in assembling the character set and states I’m aiming for—because this list of terms essentially defines the possible range of morphologies described by diatomists. Would have been nice to know about this document earlier, but at least I’ve got it now.

Time to take it down a notch. After yesterday’s distractions, I took a moment today to reflect, inspired by Beau’s thoughtful comments. It makes no sense to try and push through a three-day push when I’m distracted with other tasks, and not able to fully get into it—it devalues the three-day push and robs it of its very essence, the motivation that makes it work. So, I’ve learned from my mistakes, and put off the three-day push until such time I’m actually able to devote my energies to it.

I spent the morning instead reading Dave’s manuscript, which appeared in my inbox yesterday. It kicked me back another notch, because it’s a spectacularly negative piece of writing—essentially, it’s a punishing 42-page tractate on why the microfossil record sucks ass, and consequently can’t be used for macroevolutionary studies. Not the most inspiring thing to read when you’re working on a thesis mostly focused on using the microfossil record for macroevolutionary studies. It carefully goes through all the reasons why the record of microfossil diversity—well, basically Neptune—doesn’t represent the real history of microfossil diversity: incomplete preservation of species, collection of occurrence data for only a subset of the species actually seen by micropaleontologists (because, in essence, they’re checking presence/absence boxes on a list of biostratigraphically informative species), reworking of older fossils into newer sediments, lousy age-models, and a taxonomic system that artificially inflates species counts. Then he goes on to wax poetic about how bad this all is, and how it screws everything up. Finally, he promises to present a glimmer of hope in a last section entitled “solutions”, but this turns out to be more of a critique of why approaches taken to date don’t work. The final straw, in the “Discussions, General Recommendations and Conclusions”? The microfossil record is great, but to fix our problems we have to go back and reanalyze an entire composite section from one of each biogeographic province, this time counting every taxon that’s there. Crazy? Yes.

Had a very helpful chat with Andy on a round trip to the coffee machine—complained to him at length about this paper, and he seemed to agree with me that it was unnecessarily negative. He suggested that I could certainly encourage Dave in my comments to balance his critical eye with more positive points on the sorts of studies that can in fact be done with the record as it is.