Red hot peppers! Can evolution “design” anything, especially a chemical bomb a plant uses to be sure its seeds get spread properly?
There’s a desert plant in the Middle East that has an ingenious way of dispersing its seeds. Many plants rely on animals for help, but there’s a problem: the animal helper needs to spread the seed without destroying it. For instance, many plants surround their seeds by fleshy, delicious fruits, but if the animal munches the seeds, there they go, into oblivion instead of into the soil.
Current Biology tells the story of Ochradenus baccatus (“Taily Weed”; see photo in Flowers of Israel), a homely desert shrub that has a “mustard oil bomb” method of attracting animals but protecting its seeds from getting eaten. It attracts rodents with the delicious fruit, but if they bite into the seeds, a chemical reaction occurs between the fruit juice and the seed juice, and pow! a distasteful, toxic mustard oil bomb goes off in the mouth. The rodents quickly learn to spit out the seeds rather than eat them. Fortunately for the plant, the rodents (to avoid getting eaten by their own predators), take the fruits to their rocky habitats, the best places for the seeds to grow. This provides an especially tight example of commensal mutualism, where both parties benefit equally from their interaction.
In the Current Biology review article, K. C. Burns (U. of Wellington) did his best to evolutionize the story while admiring the designs of the plant world. First, he plagiarized the title of a well known book by Darwin champion Richard Dawkins, headlining his article, “Seed Dispersal: The Blind Bomb-Maker.” In the attempt, though, he personified evolution too often, starting right in the first paragraph:
Seed dispersal sets the stage for everything that happens to a plant during its lifetime — after germination, plants will never again be able to travel across the landscape. Seeds can’t move very far on their own, though, so they rely on wind, water or animals to get the job done. For example, coconuts float on water to reach their destination. Maple seeds fly through the air using auto-rotating wings that operate similarly to helicopter blades….
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