Are plants intelligent?

For generations humans thought that animals had no ability to feel or think in ways that we do. They were simply biological machines there purely for us to eat, exploit, hunt or use however we wanted to with no moral restrictions.

Move to modern day and we find ourselves living in societies that have laws and strict penalties for those that harm animals. We have also had to change the way we kill and prepare our meat. Animals must now be killed ‘humanely’ as we understand they feel stress and anxiety when about to be killed.

Much of the trauma that it is possible for us to inflict on animals is why many people subscribe to a vegetarian diet. They do not wish to harm animals so avoid killing and eating them, this conscientious objection often including animal products such as eggs and dairy.

But scientist Michael Pollan, author of such books as “The Omnivore’s Dilemma” and “The Botany of Desire,” says that a new field of research called plant neurobiology is finding out something amazing about plants.

“They have analagous structures,” Pollan explains. “They have ways of taking all the sensory data they gather in their everyday lives … integrate it and then behave in an appropriate way in response. And they do this without brains, which, in a way, is what’s incredible about it, because we automatically assume you need a brain to process information.”

”Researchers have played a recording of a caterpillar munching on a leaf to plants — and the plants react. They begin to secrete defensive chemicals — even though the plant isn’t really threatened, Pollan says. “It is somehow hearing what is, to it, a terrifying sound of a caterpillar munching on its leaves. In addition to hearing, taste, for example, they can sense gravity, the presence of water, or even feel that an obstruction is in the way of its roots, before coming into contact with it. Plant roots will shift direction to avoid obstacles.

So what about pain? Do plants feel? Pollan says they do respond to anesthetics. “You can put a plant out with a human anesthetic. … And not only that, plants produce their own compounds that are anesthetic to us.” But scientists are reluctant to go as far as to say they are responding to pain.

How plants sense and react is still somewhat unknown. They don’t have nerve cells like humans, but they do have a system for sending electrical signals and even produce neurotransmitters, like dopamine, serotonin and other chemicals the human brain uses to send signals.

And chalk up another human-like ability — memory.

Biologist Monica Gagliano. She presented research that suggests the mimosa pudica plant can learn from experience. Mimosa is a plant, which looks something like a fern, that collapses its leaves temporarily when it is disturbed. So Gagliano set up a contraption that would drop the mimosa plant, without hurting it. When the plant dropped, as expected, its leaves collapsed. She kept dropping the plants every five to six seconds. After five or six drops, the plants would stop responding, as if they’d learned to tune out the stimulus as irrelevent,”

But when the plants were shaken, their normal response was again seen. They had made the distinction between being shaken and being dropped. This was done every week for four weeks – the responses were the same. So they not only remembered what had occurred they remembered how to respond.

Are they watching the sun? Or watching us?

Are they watching the sun? Or watching us?

Stefano Mancuso, in his new book, Brilliant Green, says plants have evolved an incredible variety of toxic compounds to ward off predators. When attacked by an insect, many plants release a specific chemical compound. But they don’t just throw out compounds, but often release the precious chemical only in the leaf that’s under attack. Plants are both tricky and thrifty.

“Each choice a plant makes is based on this type of calculation: what is the smallest quantity of resources that will serve to solve the problem?” Mancuso writes. In other words, plants don’t just react to threats or opportunities, but must decide how far to react.

The bottom of the plant may be the most sophisticated of all though. Scientists have observed that roots do not flounder randomly but search for the best position to take in water, avoid competition and garner chemicals. In some cases, roots will alter course before they hit an obstacle, showing that plants are capable of “seeing” an obstacle through their many senses.
“Plants are wonderful communicators: they share a lot of information with neighbouring plants or with other organisms such as insects or other animals. The scent of a rose, or something less fascinating as the stench of rotting meat produced by some flowers, is a message for pollinators.”

Many plants will even warn others of their species when danger is near. If attacked by an insect, a plant will send a chemical signal to their fellows as if to say, “hey, I’m being eaten – so prepare your defences.” Researchers have even discovered that plants recognize their close kin, reacting differently to plants from the same parent as those from a different parent.

Instead of a single powerful brain, Mancuso argues that plants have a million tiny computing structures that work together in a complex network, which he compares to the Internet. The strength of this evolutionary choice is that it allows a plant to survive even after losing 90% or more of its biomass.

“The main driver of evolution in plants was to survive the massive removal of part of the body,” said Mancuso. “Thus, plants are built of a huge number of basic modules that interact as nodes of a network. Without single organs or centralised functions plants may tolerate predation without losing functionality. Internet was born for the same reason and, inevitably, reached the same solution.”

Having a single brain – just like having a single heart or a pair of lungs – would make plants much easier to kill.

“This is why plants have no brain: not because they are not intelligent, but because they would be vulnerable,” Mancuso said.

In this way, he adds, it may be better to think of a single plant as a colony, rather than an individual. Just as the death of one ant doesn’t mean the demise of the colony, so the destruction of one leaf or one root means the plant still carries on.

With so much going on in plants that we’re only just coming to realise, one could wonder just what vegetarians are going to do now…

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