Editor’s note: A correspondent sends along this remarkable nature video from the BBC and asks, given that the Venus flytrap mechanism appears to be irreducibly complex, has it been analyzed from a design perspective?
Good question! And yes it has, most recently by the wonderful Brazilian chemist Marcos Eberlin in his new book Foresight: How the Chemistry of Life Reveals Planning and Purpose, from Discovery Institute Press. We’re delighted to offer a peek at his discussion. Foresight, endorsed by no fewer than three Nobel Prize-winning scientists, is available on Amazon.
Carnivorous plants are intriguing, bizarre, and hard not to love at first sight. These plants use an arsenal of masterfully engineered moving traps, chemical and electrical sensors, and digestive chemicals to kill and consume spiders, insects, protozoans, crustaceans, lizards, mice, rats, and various other small invertebrates and vertebrates. Each of these carnivorous plants manages all this using lures and a trap device, along with a mechanism and an arsenal of chemicals to facilitate full digestion of the prey.
As Aaron Ellison and Nicholas Gotelli note, Charles Darwin pioneered modern research on carnivorous plants with his 1875 work Insectivorous Plants. There, Darwin applied his idea of homology (which modern evolutionary biologists call “homoplasy”) to highlight what he saw as evolutionary convergence across apparently unrelated taxa, and he was the first to provide descriptions of the structures that eight genera of plants use to entrap insects.
Impressive in Two Ways
As Darwin reported, these plants are impressive not only for being able to capture prey but also for employing specific enzymes to dissolve the animal proteins and then absorb them. If no enzymes were there, there would be no use for the trap at all. Although Darwin described all this nearly 150 years ago, since then no work has shown how these amazing creatures could have evolved their intricate and highly synchronized anatomical, electrical, and biochemical functions.
Carnivorous plants use highly specialized leaves that function as mechanical traps. “Many traps lure prey with bright colors, extra-floral nectaries, guide hairs, and/or leaf extensions,” writes John Brittnacher. “Once caught and killed, the prey is digested by the plant and/or partner organisms. The plant then absorbs the nutrients made available from the corpse. Most carnivorous plants will grow without consuming prey but they grow much faster and reproduce much better with nutrients derived from their prey.”
The Venus flytrap, Dionaea muscipula, is the most famous carnivorous plant. In its wild habitat in the southeastern United States, it mostly eats flies, but it will consume anything living that fits in the trap. As Rainer Hedrich and Erwin Neher explain, the plant employs highly sensitive mechanoreceptors, and “upon contact with prey an action potential is triggered which, via an electrical network — comparable to the nervous system of vertebrates — rapidly closes its bivalved trap.”
The trap snaps shut automatically, but then the plant follows a carefully orchestrated sequence of gene activation to tightly close the trap, digest the prey, and absorb the nutrients. This whole sequence of events must happen in perfect synchrony. The plant makes step-by-step decisions about activation by counting the stimuli on its sensory organs.
Beyond the Reach of a Blind Process
Evolutionary scientists have not dared to propose that the Venus flytrap evolved these animal-like skills by taking genes from its prey, a nearly impossible feat since the prey is fully digested for food. Rather, they have suggested the plant modified and rearranged gene functions that all plants share. But this too lies well beyond the reach of a blind process that cannot predict future needs.
Carnivory is found in the animal kingdom and makes the most sense there. That’s why it’s so intriguing to find this behavior in the green branch of the tree of life, especially considering that most plants seem to thrive using just photosynthesis. If carnivory evolved here to provide more nutrients, why would natural selection reward the plants — apparently able to benefit from more nutrients — for expending some of the precious nutrients they already had to evolve a not-yet-useful new nutrient supply tool, and reward these supposedly evolving plants for their seemingly far-sighted efforts over countless generations stretching over long ages? That is, if the nutrition from the carnivorous action was just a non-essential bonus for the flower, then why would nature select for all the many intermediate steps of this complex bonus system during which the system offered no benefit — neither nutrition nor protection — and likely exacted a nutrient and energy cost at the risk of survival?
If it first evolved for protection and then later evolved to provide additional nutrients, we have the same problem: Why expend all the energy on the way to a functional protection system, before the protection system was at all functional? Natural selection does not look ahead to future payoff, remember. It’s all about “What have you done for me lately?”
This challenge for Darwinism is only exacerbated by the fact that, if indeed they did evolve carnivory, these plants had to do so “independently at least six times in five angiosperm orders,” as Ellison and Gotelli explain.
A Miracle, or Six
Maybe one could grant the evolutionary miracle a single time, but six times?
Other plants, such as Darlingtonia and some Nepenthes species, are believed to have lost the ability to digest prey themselves. Perhaps the digestive system worked fine, but then the plant found itself in an environment rich enough in bacteria and other organisms that one of these plants born with a defective, poorly functioning digestive system could manage just fine. In such situations, the plant could rely on the bacteria and other organisms now in its environment to digest the nutrients from the prey it captured.
On its website, the International Carnivorous Plant Society explains this in the following way: “To put it unscientifically, why should a plant go through all the bother of digesting the prey itself when other organisms will do it for them? Or scientifically, if there is no selective advantage to expending the energy for digestion, mutations will accumulate eliminating digestion.”
Not Evolution, but Devolution
Maybe so, but that is devolution — breaking an existing system. And as anyone who has had children knows, any two-year-old can manage that. Darwinism needs to explain the evolution of new systems, new engineering marvels, not the devolution of existing ones.
Someone might complain that one just needs a bit of imagination to embrace the possibility that such plants evolved. But truly imagining a viable evolutionary pathway means describing a series of viable steps from beginning to completed trap and digestive system. Believing something happened isn’t the same as imagining how it happened. Nobody has come remotely close to doing the latter, and not for lack of trying.
Are we allowed to imagine, to consider, other possible causes — causes with the demonstrated ability to assemble novel engineering marvels? Let’s go ahead and consider another possibility, whether or not we have permission: The construction of the system required foresight of what would end up inside the trap in order to synchronize construction of an appropriate digestive system. It required foresight of a functioning digestive system to bother constructing the sophisticated trap. And foresight was required to construct each of the two systems individually.