Intelligence in Nature - Jeremy Narby [35]
Having answered my question, he continued making the case for plant plasticity. Plants have to gather resources in their local environment while facing competition from their neighbors. As they are mainly fixed in one place, the most sensible way any plant can do this is to occupy the space around itself in an optimal way. A branching structure happens to be the simplest way in which this can be done, and this is the solution plants adopt, both below ground, as they send down roots into the soil to form exploitative tissues, and above ground, as they deploy their leaves to gather the maximum amount of light. To do all this, an individual plant must perceive a gravity vector and align itself correctly. And its actual shape and morphology are determined by the quantity and quality of light it perceives. For Trewavas, this is âadaptively variable behavior within the lifetime of the individual, i.e., intelligence.â Furthermore, individual plants do not choose their environment, as seeds land and germinate where they can. Plants have to grow in a great variety of environments and adjust their structures to optimize their ability to exploit what they find.
Trewavasâs favorite example of vegetal intelligence and plasticity is a parasitic plant called dodder. It moves around by wrapping itself around other plants and correctly estimating their nutritional quality. Within an hour, dodder decides whether to exploit a host or to move on. If it stays, it takes several days before beginning to benefit from its hostâs nutrients. But dodder anticipates how fruitful its host will be by growing more or less coils. Growing more coils allows greater exploitation; but if the host is poor in nutrients, this wastes precious energy, because dodder lacks leaves and relies on its hosts for water and food. So it has to make correct decisions or face death. Botanist Colleen Kelly, working in the early 1990s, found that dodder correctly assesses when to eat and when to move on, and that its foraging strategies have the same efficacy as those of animal foragers. And it computes the right choice between close alternatives without the benefit of a brain.
Trewavas described plants as having intention. But I had in mind Jacques Monodâs statement that attributing purpose or goals to nature contradicts the central method of science. According to Monod, studying nature scientifically means ignoring the possibility of intention. I reminded Trewavas of this postulate and added that he seemed to have crossed the line.
He scoffed: âWell, I donât know how many people actually believe Jacques Monod in that regard. That was an idea that did not really apply to humans, did it? It seemed to devitalize life in my own view. It seemed to indicate that life was solely governed by chance. And animals have foresight. And so do we. And to me, plasticity must be foresight, because itâs the ability to adjust to the particular environmental conditions which you find. If you didnât have that ability, then you would not be able to accommodate optimally to that. Possessing plasticity is in a sense foresight of the possible conditions in which the plant will actually find itself.â
How, then, does a plant make up its mind? I asked. Trewavas replied that he had pondered this question for many years. In 1990, he and his colleagues had a breakthrough. They were studying how plants perceive signals and transmit information internally. Using genetic manipulation, the scientists inserted into tobacco plants a protein that makes them glow when calcium levels rise inside their cells. They suspected changes in cellular calcium concentration to be a major means by which plants perceive external events. To their amazement, they found the tobacco plants responded immediately to touch. Though tobacco is not known to be touch-sensitive, one gentle stroke caused the modified plants to glow with the light produced by the elevation of calcium inside their cells. Trewavas was dazzled by the speed of the response: âIt was