Plants don't think, they grow: The case against plant consciousness

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If a tree falls, and no one's there to hear it, does it feel pain and loneliness? No, experts argue in an opinion article publishing on July 3rd in the journal Trends in Plant Science. They draw this conclusion from the research of Todd Feinberg and Jon Mallatt, which explores the evolution of consciousness through comparative studies of simple and complex animal brains.

"Feinberg and Mallatt concluded that only vertebrates, arthropods, and cephalopods possess the threshold brain structure for consciousness. And if there are animals that don't have consciousness, then you can be pretty confident that , which don't even have neurons—let alone brains—don't have it either," says Lincoln Taiz, Professor Emeritus of molecular, cell, and at University of California at Santa Cruz.

The topic of whether plants can think, learn, and intentionally choose their actions has been under debate since the establishment of plant neurobiology as a field in 2006 (10.1016/j.tplants.2006.06.009). Taiz was an original signer of a letter, also in Trends in Plant Science (10.1016/j.tplants.2007.03.002), arguing against the suggestion that plants have neurobiology to study at all.

"The biggest danger of anthropomorphizing plants in research is that it undermines the objectivity of the researcher," Taiz says. "What we've seen is that plants and animals evolved very different life strategies. The brain is very expensive organ, and there's absolutely no advantage to the plant to have a highly developed ."

Plant neurobiology proponents draw parallels between electrical signaling in plants and nervous systems in animals. But Taiz and his co-authors argue that the proponents draw this parallel by describing the brain as something no more complex than a sponge. The Feinberg-Mallatt model of consciousness, by contrast, describes a specific level of organizational complexity of the that is required for subjective experience.

Plants use in two ways: to regulate the distribution of charged molecules across membranes and to send messages long-distance across the organism. In the former, a plant's leaves might curl up because the movement of ions resulted in movement of water out of the cells, which changes their shape; and in the latter, an insect bite on one leaf might initiate defense responses of distant leaves. Both actions can appear like a plant is choosing to react to a stimulus, but Taiz and his co-authors emphasize that these responses are genetically encoded and have been fine-tuned through generations of natural selection.

"I feel a special responsibility to take a public position because I'm a co-author of a plant physiology textbook," he says. "I know a lot of people in the plant neurobiology community would like to see their field in the textbooks, but so far, there are just too many unanswered questions."

One frequently referenced study on plant learning is the apparent habituation of Mimosa pudica (10.1007/s00442-013-2873-7). In this experiment, a plant is dropped, and its leaves curl up in defense. After being dropped many times, but sustaining no serious damage, the leaves stop curling. When the plant is shaken, the leaves do curl, ostensibly ruling out motor fatigue as a cause of the lack of response when dropped.

"The shaking was actually quite violent. Because the shaking stimulus was stronger than the dropping stimulus, it doesn't definitively rule out sensory adaptation, which doesn't involve learning," Taiz argues. "Related experiments with peas purporting to show Pavlovian classical conditioning are also problematical because of the lack of sufficient controls."

Taiz and his co-authors hope that further research will address the questions left unanswered by current plant neurobiology experiments by using more stringent conditions and controls.


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More information: Trends in Plant Science, Taiz et al.: "Plants Neither Possess Nor Require Consciousness" https://www.cell.com/trends/plant-science/fulltext/S1360-1385(19)30126-8 , DOI: 10.1016/j.tplants.2019.05.008
Journal information: Trends in Plant Science

Provided by Cell Press
Citation: Plants don't think, they grow: The case against plant consciousness (2019, July 3) retrieved 15 October 2019 from https://phys.org/news/2019-07-dont-case-consciousness.html
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mqr
Jul 03, 2019
Most humans do not think either. They just grow too. If thinking = human, then there are very few humans in the planet earth.

Jul 03, 2019
NO no no… not even close. The infinite universe is created by consciousness. EVERYTHING is consciousness, but Cell Press obviously:) In fact this article ridiculous.

Jul 03, 2019
How does consciousness arise in the brain? Do we really have a handle on that? If not, how can we say that there is a threshold below which consciousness does not exist. It could be argued that an amoeba has awareness of its surroundings and reacts to threats, and isn't that awareness a sort of consciousness?

Jul 03, 2019
Claudius that's the thing, after enough talk about it, we all realize consciousness has no agreed definition at all. Articles like this need to argue plants don't have consciousness definition 7A.2 or 3K.4 or whatever.

Jul 03, 2019
Considering some of the most parsimonious physics concerning the TOE point to a strong potential for consciousness being a field just like gravity.....hard to imagine this kind of garbage gets published. What a hit job piece. Thanks to all the reviewers of this paper for putting more garbage in the system. Not that they might be right....anything is possible.....but to be so SURE that you are right.......arrogance and ignorance of the highest level. The editors at Phys.org should be ashamed of themselves.

Jul 04, 2019
Just curious; Are there any "plant lunatic asylums" and formally qualified "plant psychiatrists" out there?

Jul 04, 2019
The same people who are anti-vaxxers, believe MSG and gluten are somehow harmful, and want to make French Fries out of cauliflower, believe plants are conscious.

Jul 04, 2019
well shootsownfoot

i's have bet that the plants
are thinking

"don't eat me!"
"don't eat me!"
"don't eat me!"

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