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What if your own theory was tricking you? What if the theory your research was based on was just a “Clever Hans”? Out today in TREE, we explore this problem and more. In this 🧵 I will elaborate the Clever Hans problem in biological theory.

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Dustin Marshall @djmmeeg.bsky.social · 28/05/2026

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Thanks! Yes assumptions are unavoidable

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That a theory predict data is a necessary but insufficient condition for a theory to be sound. So rather than just focusing on fit we recommend that biologists spend more time scrutinising the assumptions of competing theories. some theories are merely Clever Hans, the challenge is to find them.

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the big problem is that in biology, we tend not only conflate prediction with explanation, we also assess the virtue of theories based solely on their fit to data. Numerous debates for many biological theories focused on relative fit but we think this is the wrong focus.

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Have We Outgrown the Existing Models of Growth?

For example, several different models all predict growth trajectories equally well, but because they have different underlying mechanics, they can’t all explain growth equally well www.sciencedirect.com/science/arti...

sciencedirect.com

Theories of growth have a long history in biology. Two major branches of theory (mechanistic and phenomenological) describe the dynamics of growth and…

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The problem is, when these theories, which we developed to fit the data, then fit the data, we can then be tempted to infer that the theory explains the data. We have succumbed to the prediction-explanation fallacy.

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We usually build theories based on a series of biological principles and an expectation of what output seems reasonable from a theory. Biological theories aren’t derived out of thin air, we want them to have certain dynamics. e.g theories of growth should predict growth to be fast as first then slow

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Of course Hans couldn’t actually do math, he was just trained to stop tapping when the human asking the question gave inadvertent clues that he’d arrived at the same answer. Theories can be like that. They can give the right answer (predictions match data), tempting us to infer they EXPLAIN BUT!

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Clever Hans was a horse that seemed able to calculate complex mathematica problems and tap out the right answer with his hoof en.wikipedia.org/wiki/Clever_...

en.wikipedia.org

Clever Hans - Wikipedia

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Reposted by Dustin Marshall

When cells are in more realistic regimes, resource fluxes actually scale with radius rather surface area. And things get even more complicated when cells swim….the point here is that all three scalings are ”first principles approaches” but they are not all equally applicable

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Reposted by Dustin Marshall

Princess Bride: Classic Blunders!

For example, how do resource fluxes scale with cell size? most people would guess 2/3’s because of simple intuition about surface volume ratios but that only works under unrealistic conditions of stationary cells and saturating resources.

static.klipy.com

ALT: Princess Bride: Classic Blunders!

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Princess Bride: Classic Blunders!

static.klipy.com

ALT: Princess Bride: Classic Blunders!

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Reposted by Dustin Marshall

Second thoughts about first principles in biology

Out today in @cp-trendsecolevo.bsky.social our paper “Second Thoughts about First Principles in Biology.” www.cell.com/trends/ecolo... . We are in favour of first principles approaches in biology but we think that we need to do better in how we use them.

cell.com

First-principles approaches, based on physics or chemistry, are key pillars of biological theory. Despite their value, there are recurrent problems with many first-principles approaches in biology: th...

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Second thoughts about first principles in biology

cell.com

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Such fallacies are likely to proliferate in a machine learning and causal analyses era but we should avoid them. thanks to a truly excellent editorial process with thoughtful comments all round, im really pleased with the final product. thanks to the coauthors and colleagues for excellent chats

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Finally we ask that biologists move past assessing theories solely on fit to data. Fit to data is a necessary but insufficient condition for validating a theory. concluding that, because a theory fits data, it explains those data is to succumb to the prediction-explanation fallacy.

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We have noticed that many first principle approaches can have esoteric, if not downright weird biological assumptions at their core. but these biological assumptions go unscrutinised because of the intimidating physics they’re attached to. Physics can act as a Trojan horse for weird biology

But larger fish swim faster and , have different ventilation rates, while water becomes thinner and more permeable to oxygen diffusion in warmer temperatures such that more complete treatments of oxygen uptake conclude that larger fish do just fine in warmer water

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School of Biological Sciences, Monash @MonashBiol @monashbiol.bsky.social · 19/05/2026

Another common error in first principles approaches in biology is to use incomplete physics: e.g. theories of oxygen transport in fishes assume that only gill area changes with fish size and temperature, concluding that warmer temperatures favor smaller fish

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Reposted by Dustin Marshall

Does it matter if single celled organisms are getting smaller as the world gets hotter? @djmmeeg.bsky.social and colleagues found that size-function relationships have been mis-estimated with worrying consequences for global carbon pumps. pubmed.ncbi.nlm.nih.gov/42087558/

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Reposted by Dustin Marshall

ARC Tracker @arc-tracker.bsky.social · 13/05/2026

Nothing in the Budget last night for the ARC. Despite review after review recommending ARC funding be increased, nothing. Year on year, the same thing, no matter who's in Government.

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Reposted by Dustin Marshall

Drivers and Consequences of Size Declines in Unicells

Metabolic scaling is thought to scale very steeply with size in unicells but what if that steepness is simply an artefact? Out today in Ecology Letters, we show that metabolic scaling is not superlinear in unicells but instead scales at ~0.86 onlinelibrary.wiley.com/doi/epdf/10....

onlinelibrary.wiley.com

Reader environment loaded

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Drivers and Consequences of Size Declines in Unicells

onlinelibrary.wiley.com

Reader environment loaded

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Dustin Marshall @djmmeeg.bsky.social · 07/05/2026

”Metabolic scaling is thought to scale steeply”….? Maybe I shouldn’t write these things before I’ve had coffee. it should be “Metabolism is though to scale steeply…..”

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Thanks to the great editorial team at ELE and my co-authors. we’d love to hear people’s thoughts. This is just the start of our work in these issues so reach out if interested.

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If we wish to predict how warming mediated size declines will alter the function of microbial communities, we need accurate estimates of size function relationships

This misestimation matters because cells are getting smaller as the world warms (below preliminary evidence that cells shrink with warming in bacteria and yeast)

Once we account for these density effects, metabolic scaling drops dramatically. the scaling of photosynthesis and other functions with cell size are almost certainly misstated for the same reason

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Elizabeth Spiers @espiers.bsky.social · 01/04/2026

Lots of studies find superlinear scaling in unicells but these studies failed to account for population density in the metabolic chamber. Because higher densities suppress metabolic rate, and because studies that study smaller cells use higher densities, density effect confound size effects

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Reposted by Dustin Marshall

I recently re-read Richard Hofstadter’s Anti-Intellectualism in American Life and now every time a Silicon Valley billionaire opens his mouth, I think about it. So I wrote about it for The Nation: www.thenation.com/article/soci...

thenation.com

The Anti-Intellectualism of the Silicon Valley Elite

How the self-styled know-it-alls atop the knowledge economy want to dismantle the pursuit of knowledge for its own sake

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Reposted by Dustin Marshall

School of Biological Sciences, Monash @MonashBiol @monashbiol.bsky.social · 23/03/2026

How will evolution affect survival and yields of common fisheries species? A recent study by Jan Kozlowski, @djmmeeg.bsky.social @craig-white.bsky.social found that fish will evolve to survive warmer temperatures AND smaller sizes, reducing fisheries yields by ~50% www.science.org/doi/full/10....

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thanks for the shout out Robert! However, I would describe this more as temperature induced evolutions impacts on fisheries. Evolutionary impacts of fisheries is a different thing to me.

Great question! Range changes will happen for species where their niche (food, habitat) also changes with them: our model overestimates impacts on these. It’s unclear how many species can perfectly track temperature, we suspect most species are moving a bit but not enough to experience no warming

Reposted by Dustin Marshall

Evolutionary adaptation to global change reduces sustainable fisheries yields

Fish will have to adapt to a warming world, what will that adaptation do to fisheries yields? We answer that question today in Science. I’ll summarise our findings very briefly in this thread www.science.org/doi/epdf/10....

science.org

Global warming is altering the fisheries that underpin food security, but projections of these impacts generally exclude evolutionary processes. We describe a model that forecasts how fish will adapt ...

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Reposted by Dustin Marshall

Dustin Marshall @djmmeeg.bsky.social · 12/03/2026

Out today in @science.org our paper on how evolutionary adaptation to warming will reduce fisheries yields. Please let me know if you need me to send you a copy. Summary of the paper coming soon. www.science.org/doi/10.1126/...

science.org

Evolutionary adaptation to global change reduces sustainable fisheries yields

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What’s the catch of the day?

Thanks to the authorship team, some amazing, thoughtful reviews and our groups. also check out the excellent commentary here www.science.org/doi/10.1126/...

science.org

Warming oceans and evolution make fish less likely to be on the menu

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We hope that our life history optimisation approach might be useful for exploring the impacts of adaptation to warming more generally. we usually think about evolutionary rescue as being a good thing: it is for the species of interest but it will not leave associated ecosystem services unscathed.

Summing across the largest the largest fisheries in the world, the preficted losses due to adaptation are staggering

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But under more extreme warming, fisheries losses also become more extreme, yet another good reason why every bit of warming counts

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There is quite a bit of variation but generally higher temperatures mean more evolution and therefore greater losses, under middle of the road warming, it looks like this

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we find that evolution is good for fish fitness, fish regain some of their lost fitness if they adapt to warmer conditions. BUT this adaptation reduces fisheries yields, worsening the impacts of warming.

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using this temperature = death proxy, when then ask how might fish life histories evolve to future warmer conditions, with their associated higher mortality rates. this approach allows us to model the ”vibe“ of temperature effects via their influence on mortality rather than any one specific effect.

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We first look at ~3000 spp. and show that temperature is a good proxy for mortality rate, which in turn is a good predictor of key life history traits such as size, timing of maturity etc