Can even a single-celled organism truly learn? In Episode 70, Jeremy Gunawardena with the Department of Systems Biology at Harvard Medical School talks with us about his replication of an experiment originally conducted over a century ago, which suggested that at least one single-cell organism – the trumpet-shaped Stentor roeseli – is able to carry out surprisingly complex decision-making behaviors. His article, A complex hierarchy of avoidance behaviors in a single-cell eukaryote,” [PDF] was co-authored with Joseph Dexter & Sudhakaran Prabakaran, and published on December 16, 2019 in the journal Current Biology.

The Minds of Single-celled Organisms - Jeremy Gunawardena
The Minds of Single-celled Organisms - Jeremy Gunawardena
The Minds of Single-celled Organisms - Jeremy Gunawardena The Minds of Single-celled Organisms - Jeremy Gunawardena
@rwatkins says:
Next time, in episode 71 of Parsing Science, we’ll be joined by Verónica Sevillano from the department of Social and Methodology Psychology at the Universidad Autónoma de Madrid. She'll discuss her research into our social perceptions of animals, and how she's applying intergroup relations theory to understanding why we adore some animals, but despise others.
@rwatkins says:
Though published in the journal Current Biology, Jeremy and his team's paper touches on various other fields, including history, mathematics, and cognitive science ... and even has implications for philosophy and consciousness. So we ended our conversation by asking him what it was that led him - as a mathematician - to gravitate towards looking at biology in these counterintuitive ways.
@rwatkins says:
While anyone who owns a dog or cat will tell you that “yes, of course non-humans can also think,” the further you stray from mammals, the more dubious this claim becomes. Nevertheless, the Stentor roeseli certainly seem to exhibit some form of learning, which implies that they also experience cognition ... and - for any creature - that possibility opens up questions about consciousness, free will, and choice. So we asked Jeremy his thoughts ... on just what counts ... as thinking.
@rwatkins says:
Jeremy and his partners found that the Stentor roeseli carried out the behaviors in a non-random order, just as Jennings reported: first, they were more likely to give up and detach from their holdfast only after first altering their cilia … or bending away. And secondly, they found that this alteration … or bending was more likely to happen before contraction than after it. But, curiously, Jeremy found that the likelihood that the Stentor roeseli would either contract - or detach - were as random as a coin toss, as he explains next.
@rwatkins says:
After months of practice handling the Stentor roeseli, Jeremy and his team felt ready to carry out their own replication to see if the organism could really exhibit a hierarchy of behavioral responses or not. Ryan and I were interested in learning more about how they carried out their analyses and what it was that they found.
@rwatkins says:
We'll hear just what it is, after this short break.
@rwatkins says:
Jennings' observation that these four avoidance behaviors existed in a neat order of ranked preference suggested that the Stentor roeseli were making relatively complex decision-making calculations ... something that fascinated Jeremy. But later he learned that an attempt made by two researchers from the University of Nebraska in the 1960s failed to replicate Jennings' findings. This bothered him, so Jeremy set out to unravel what might be responsible for this discrepancy, as he explains next.
@rwatkins says:
While an organism as wide as the side-view of paperclip is certainly large enough to see with the naked eye, Doug and I figured they still must be rather difficult to experiment with ... especially given the technology available to Jennings in the early 1900s. We asked Jeremy to describe how Jennings' carried out his experiment into the Stentor roeseli, as well as what it was that he found.
@rwatkins says:
Ryan and I followed up by asking Jeremy when he first learned of the Stentor roeseli and how he became interested in researching them himself.
@rwatkins says:
The term "gene" was coined in 1905, just a year before the early geneticist, Herbert Spencer Jennings, published a paper that Jeremy and his partners set out to replicate over 100 years later. So we followed up by asking him to tell us more about Jennings and his contributions to science.
@rwatkins says:
The single-celled organism that Jeremy and his team experimented with is called Stentor roeseli. As neither Ryan nor I had previously heard of them, we started out by asking Jeremy to tell us more about what they're like, and what's so striking about their behavior.
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Hosts / Producers

Doug Leigh & Ryan Watkins

How to Cite

Leigh, D., Watkins, R., & Gunawardena, J.. (2020). Parsing Science – The minds of single-celled organisms. figshare.


What’s The Angle? by Shane Ivers


Jeremy Gunawardena: How on Earth from pure stochasticity does the organism or evolution find a way to get a probability that’s so close to a half?

Doug Leigh: This is Parsing Science: The unpublished stories behind world’s most compelling science as told by the researchers themselves. I’m Doug Leigh.

Ryan Watkins: And I’m Ryan Watkins. Today, in episode 70 of Parsing Science, we’re joined by Jeremy Gunawardena from the Department of Systems Biology at Harvard Medical School. He’ll discuss his research replicating an experiment originally conducted over a century ago, confirming that a single-cell organism – with no neurons – is capable of surprisingly complex decision-making behaviors … which may constitute “cognition.” Here’s Jeremy Gunawardena.

Gunawardena: I’m Jeremy Gunawardena. I’m an associate professor in the Department of Systems Biology at Harvard Medical School. I was born in Sri Lanka … Ceylon, as it was called at the time. I grew up in England. My father was in the Foreign Service. We got transferred to England and England became home. And in fact, I was a pure mathematician. At the time I was doing pure maths. If anybody had told me I would be working in a medical school and studying biology, I would have fallen off my chair laughing. One of my problems is a pure mathematician – I don’t know if it was a problem – but it made me a little bit different from some of my colleagues was that I loved pure mathematics. I loved it’s rigor and clarity and beauty. But I also wanted to have some impact in the world. That schizophrenia never left me and it took me sort of sideways because … I was a postdoc at University of Chicago and we’re just setting up a computer science program there and I got sort of sidetracked into teaching computer science. And that was just, you know, a hobby. It wasn’t work. Maths was work and computer science was play. But teaching computer science sort of opened my eyes to the idea that pure mathematics could be used to study very complicated complex systems. And that took me into industry for a while. And it took me a while to realize that computing systems: they’re great fun, they’re complicated, but they’re not really complex. And that realization sort of came about roughly about the time when the genome projects were starting. And I suddenly sort of wake up to this idea that complexity is really to be found in the living world and that biology is the source of it. And I didn’t actually think I was going to leave industry, but I had opportunity to come to Harvard as a visitor. And that was one of those experiences that completely change my own thinking. I realized that all the things I thought were interesting were actually wrong – or the wrong direction to take – and ultimately led to the position I have here, where I find myself, you know, sort of immersed in a biological world and trying to make sense of it with tools from mathematics.

Leigh: The single-celled organism that Jeremy and his team experimented with is called Stentor roeseli. As neither Ryan nor I had previously heard of them, we started out by asking Jeremy to tell us more about what they’re like, and what’s so striking about their behavior.

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