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Even Bacteria Are Purpose-Driven

The recent finding that bacteria can make individual decisions may help design better antibiotics

It used to be assumed that all microbes automatically moved away from harmful substances (chemotaxis) and toward attractive ones. Researchers assumed that there were few or no individual differences. But now, we learn from ScienceDaily:

Until now, scientists have generally considered the chemotactic properties of bacteria to be a common feature of a species or population — as if all cells behaved more or less the same. In this case, average values are sufficient to describe their movement behaviour. Now, researchers at ETH Zurich have observed the chemotaxis of bacteria in a behavioural experiment. “If you look with the appropriate technology, you’ll find astonishing behavioural differences even within a population of genetically identical cells,” report Mehdi Salek and Francesco Carrara, the lead authors of a study recently published in Nature Communications.

Paper. [The paper is open access.] – M. Mehdi Salek, Francesco Carrara, Vicente Fernandez, Jeffrey S. Guasto, Roman Stocker. Bacterial chemotaxis in a microfluidic T-maze reveals strong phenotypic heterogeneity in chemotactic sensitivity. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-09521-2 More.
Bacteria navigating a maze (art)/ETH Zurich

How do the ETH Zurich researchers know this? They constructed a downward sloping maze with either more or less nourishment (chemoattractant) at each junction and most of it at the bottom. Each bacterium (wild Marinobacter adhaerens) had to make an individual decision at each junction.

But they didn’t all go with the stronger smell, as expected. Even genetically identical bacteria (clones) made different decisions which way to go. Those who followed the crowd toward the stronger scent found more food but also more competition; those who took the road less traveled found less of both.

And what does it mean? Well, two things. First, the researchers say, individual behavior may factor in antibiotic resistance: All bacteria won’t respond in the same way even when they have identical chemical makeup. One of them offers, “Non-genetic diversity has long been known in the biomedical life sciences; for example, it is thought to play a role in antibiotic resistance. Now, environmental scientists have shown that this diversity also affects fundamental behaviours of bacteria, such as locomotion and chemotaxis — further expanding the concept of bacterial individuality.”

The researchers are not saying that the bacteria think like, say, apes or cats. They have neither the mental equipment nor the need. And yet, driven to stay alive, they make individual decisions.

There’s a name for that: teleonomy, a term coined from teleology, the study of purpose in nature:

For more than a century, biology has struggled with the concept of teleology. Teleology is the orientation of objects (often organisms) towards ends. That is, organisms have purposes which are reflected in their behaviors. What makes biology unique as a subject is that while the study of rocks or atoms rarely makes reference to purpose, the study of biology is almost exclusively concerned with purpose.

Jonathan Bartlett , “Evolutionary Teleonomy as a Unifying Principle for the Extended Evolutionary Synthesis” at BIO-Complexity

The modern synthesis (Darwinian evolution) sought to banish the idea of purpose from nature, even human nature. Like the Big Bang, purpose in nature can be seen as an argument for God. As Bartlett recounts, the word “teleonomy” was coined instead: “ to the extent that organisms operate according to their genetic programming, ‘purpose’ can simply refer to the actions of the program behind the organism.”

But as we have just seen, bacteria do not operate simply according to their genetic program.

Does this mean that bacteria have free will? Not really; as Michael Egnor reminds us, free will is an immaterial quality of the reasoning mind. Life forms that lack a reasoning mind make decisions based only on their needs or desires. Whether their decisions are “free” may involve factors irrelevant to those we usually consider when discussing human free will. Quantum mechanics may play a role.

The big news is, we live in a world where even bacteria are purpose-driven.

See also: Is an amoeba smarter than your computer? (about some things, yes)

Can plants be as smart as animals?


Quantum mechanics gives nature free will (Robert J. Marks)

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Even Bacteria Are Purpose-Driven