Friday, 31 May 2013

The Happening: Science Fact or Science Fiction?

The Happening: Science Fact or Science Fiction?

" I’ve not heard of any experiments that would be considered scientifically sound that would confirm that plants respond in any positive or negative way to human stimulus. I’d say that’s clearly over the line." David Caron;

5 Reasons Why Researchers Say The Happening Is Junk Science:

1. Plants Can Talk to Each Other
Throughout the course of The Happening, the foliage gets furious at the mere presence of humans: First it's the city parks attacking the urban masses, then the prairie fields going after country roads. The deadly pattern, radiating outward within 36 hours, leads the nursery owner to surmise that plants are communicating, then releasing toxins to specific areas. "If you take a very broad definition of communication, which means any type of signal that is made by one organism that can be sensed by another, then yes, under some circumstances, plants can communicate," says Joe Armstrong, a professor of botany at the University of Illinois.

Still, it's not a communication like a conversation. Instead, plants sense the presence of other vegetation through photoreceptors and chemical means. When herbivores chew on some types, for example, a plant's response is two-fold: chemical, to deter the herbivore; and a volatile emission into the air that other plants can sense, then respond with protective chemicals. The same chemicals are not produced when leaves are simply torn or damaged. Some plants have been shown to recognize others nearby that are competing for sunlight--ripening fruits release hormones that can cause a response in surrounding plants, and parasitic plants can sense chemicals emitted into the air and soil by other plants.

There's even research to suggest that plants may have a social life that we, as yet, don't understand: According to a recently released study by scientists at McMaster University in Hamilton, Ontario, the Great Lakes sea rocket weed can recognize plants related to it. "This is important," says Susan A. Dudley, an evolutionary plant biologist who conducted the study, "since places often live with relatives and, like animals, can increase their fitness by benefiting relatives." It's neat stuff, but hardly adds up to a crosscountry network of conniving, chatty trees.

2. Plants Can Sniper Enemies
The Happening's ominous nurseryman claims that plants can target specific threats. He cites tobacco as an example, which he insists releases certain wasp-calling pheromones as caterpillars munch on it; when the wasps show up, they kill the caterpillars.

While some plants can target specific plants, the film seemed to imply that the plants were purposefully, knowingly going directly after humans--and that's not exactly how it works. "[Some] plants send out volatile hormones when they are attacked," Dudley says. "The signals are evoked by a combination of damage and insect saliva. Predators such as wasps use this cue to find their prey." In other words, says Armstrong, in all likelihood wasps have developed sensory apparatus to detect injured plant hormones. So it's not the plant that's calling the wasp to its defense.

3. Plants Can Wage War With Genetics
Shyamalan seems to suggest that plants might evolve to the point of attack because humans pose a threat to the planet. But Armstrong stresses that individuals don't evolve--populations do, by selecting for genetic variants that promote survival. How quickly it happens all depends on how fast those plants reproduce. "Something like trees are going to be very slow because their generation time is low," he says. "Something like weeds can evolve pretty fast."

In the case of the killer vegetation, some plants would have had to come up with the killer genetic variant randomly, and over time those plants would have to have been selected because they were more fit than their less toxic relatives. Only in this case, it's not at all clear why killing humans would help these plants evolve--especially in places like parks.

Plus, says Jenny Cruse-Sanders, director of research and conservation at the Atlanta Botanical Garden, "it's unlikely across the entire plant kingdom that all these unrelated species would be producing the same compound." Armstrong agrees: "There are many different types of defense mechanisms," he says.

4. Plants Can Breathe Poison
Botanists agree that plants can emit volatile compounds. There are literally thousands of plants that have neurological impacts on humans when ingested, but researchers have yet to discover any that can emit airborne neurotoxins. And there's certainly no evidence to suggest that plants will emit them on a massive scale, because developing chemical defenses requires extraordinary amounts of energy.

Producing even simple defense mechanisms has a high energy cost--particularly for big organisms like trees and common, but inefficient, species such as grass. "For the most part, trees are big organisms and things eating them are small organisms," Armstrong says. "Under those circumstances, why expend the energy for chemical defenses?" Grasses, says Sanders, grow quickly and don't put a lot of resources into the structure or seeds--so the likelihood that they'd be able to emit toxins is nil.

Smaller plants with smaller populations, however, are a different story. "When getting eaten is a problem for smaller plants, that's a common situation where plants are toxic," Armstrong says. But that's not the scenario depicted in The Happening, in which characters spend the bulk of their time running from toxins in the fields of Central Pennsylvania--not exactly the hub of exotic plant life.

5. Plants Can Hear Us
All of our scientists agree that plants can respond to certain stimuli--it's a phenomenon called tropism--but speech isn't one of them. "You can talk to them an awful lot, and raise the CO2 content in their vicinity," Armstrong jokes, "[but] I don't think plants can sense our presence. There are plants that respond to touch--carnivorous plants like the venus fly trap have trigger hairs, and if you touch them in the right sequence, the plant will close. I don't think most other plants have a mechanism for responding to the presence or lack of presence of people."





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