In The film the Happening multiple species of plants have evolved to produce an airborne neurotoxin that targets humans because human pollution threatens plant survival. Apparently plants cannot successfully evolve a trait that protects them from human pollution, so they evolve a neurotoxin that target humans. When humans are targeted by the plant neurotoxin they become paralyzed and then kill themselves because our self-survival instinct has been damaged by this neurotoxin.

However, there is no reason to believe plants could know that humans produce pollution. If anything, plants would react to pollution without any knowledge of its origin as if it was a natural airborne gas. Plants would evolve a defense mechanism against pollution instead of against humans. Greater thickness in plant material or greater resistance to certain airborne pollutants could be more plausible evolutionary traits.

Morevoer, it would take plants generations to develop an evolutionary trait that targets human pollution or human populations, and given the long time it takes for trees to age and reproduce, for instance, giant sequuoi that can live up to 3,000 years and the bristlecone pine that can live can live beyond four-thousand years, could only have developed over thousands of years of evolution. Since most major human pollution began with the industrial revolution which occurred a few hundred years ago, it would be impossible for plants to evolve traits that protect them from pollution within a short period of time. Moreover, given the diversity in plant reproduction cycles and lifespans, it would be impossible for a single shared adaptation to occur simultaneously among all of these plants. It seems that if plants where such environmentalists, they would develop some way to stop cow farts, which could be disastrous to global warming.

This film is also erroneous in assuming that humans are a danger to plant survival because humans have a symbiotic mutualism between many plant species, especially agricultural plants. For instance, corn could not exist without humans planting corn seeds. Thus, to continue the line of thought and sort of science fiction proposed by this film, there could be a sort of plant wars that emerges, agricultural plants versus human-hating plants, where the fate of humanity lies in the balance. The Happening 2: The fate of humanity lies in agricultural human-loving plants, pitted against misanthropic plants.

Moreover, Humans have similar nervous systems and brains to animals, so there is no reason for the plant neurotoxin to target humans instead of other animal life. That is, animals and humans share many of the same biological organs and as such illnesses and biological vultnurabilities. For instance, animals react adversely to pollen just as humans do, and domesticated dogs get cancer as much as humans do. It is sheer nonsense to think that plants could produce a neurotoxin that targets only humans. Humans can't even do that, and we actually have thinking brains. Moreover, even if plants produce neurotoxins that target humans, these would be detectable and likely treatable. Anyone with access to a biological laboratory with a decent microscope and biohazard suit could enter the danger zone, retrieve samples of the neurotoxin and the plants that produce them, and return safely to a laboratory for research and treatment.

This film explores the evolutionary struggle of plant life with human-produced pollution. Humans cope with pollution as well, however New technologies will bring human-made pollution back to a minimal level like before the industrial revolution. Plants will continue to evolve defenses against other plants, animals, toxic chemicals, and micro-organisms, such as viruses and bacteria, and animals and microorganisms will do much the same, however it is humans whose dependence on evolution for survival will be minimal, existing in large part to resist against toxic chemicals and microorganisms, for we are more or less invulnerable to animal and plant life. And when humans reproduce and survive equally human evolution will be no more.