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Did you know your summer picnics are part of this symbiotic interplay?


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Did you know your summer picnics are part of this symbiotic interplay?

  • Did you know your summer picnics are part of this symbiotic interplay?

  • We can relate to the rodents’ plight. Watermelons (Citrullus lanatus) are filled with large seeds, and most of us spit them out before swallowing the juicy pulp, largely because the seeds have a sour taste. This sour taste is our bodies’ way of telling us that the seeds are defended chemically. By listening to our taste buds and spitting the seeds out, we avoid investing the energy to metabolise these defensive chemicals and avoid any harmful effect they might have after ingestion. However, in the case of O. baccatus, it is the combination of chemicals stored separately in the fruit pulp and in the seeds that creates the chemical deterrent, not just the seeds themselves.



Here’s where Burns mixed his metaphors.  He reminded us that human engineers have designed bombs that don’t detonate till two components mix, but then attributed a similar “design” to the unguided processes of evolution.  He first presented the “evolutionary conundrum” for plants needing seed dispersers without attracting seed predators.  He claimed that the Taily Weed and rodent “co-evolved” their mutualistic dance of seed dispersal and feeding.  And then in the case of the chili pepper, he said, “capsaicin triggers receptors located in mammalian mouths that have been designed by evolution to respond to excessive heat.”  Burns never quite bothered to explain how the complex secondary metabolites in the fruit (glucosinolates) and the enzyme (myrosinase) in the seeds that detonates the “mustard oil bomb” evolved by mutation and natural selection in the first place, let alone the complex heat receptors in the mammalian mouth.

  • Here’s where Burns mixed his metaphors.  He reminded us that human engineers have designed bombs that don’t detonate till two components mix, but then attributed a similar “design” to the unguided processes of evolution.  He first presented the “evolutionary conundrum” for plants needing seed dispersers without attracting seed predators.  He claimed that the Taily Weed and rodent “co-evolved” their mutualistic dance of seed dispersal and feeding.  And then in the case of the chili pepper, he said, “capsaicin triggers receptors located in mammalian mouths that have been designed by evolution to respond to excessive heat.”  Burns never quite bothered to explain how the complex secondary metabolites in the fruit (glucosinolates) and the enzyme (myrosinase) in the seeds that detonates the “mustard oil bomb” evolved by mutation and natural selection in the first place, let alone the complex heat receptors in the mammalian mouth.



It’s noteworthy that the main paper Burns was summarizing said nothing about evolution (Samuni-Blank et al., “Intraspecific Directed Deterrence by the Mustard Oil Bomb in a Desert Plant,” Current Biology, Volume 22, Issue 13, 1218–1220, 14 June 2012, 10.1016/j.cub.2012.04.051).  In fact, it begins with a 4-minute video narrated cheerfully by lead author Michal Samuni-Blank (Israel Institute of Technology), who describes, without mentioning evolution once, how her team discovered and tested the “directed deterrence hypothesis” with chemical analysis and good old field work.

  • It’s noteworthy that the main paper Burns was summarizing said nothing about evolution (Samuni-Blank et al., “Intraspecific Directed Deterrence by the Mustard Oil Bomb in a Desert Plant,” Current Biology, Volume 22, Issue 13, 1218–1220, 14 June 2012, 10.1016/j.cub.2012.04.051).  In fact, it begins with a 4-minute video narrated cheerfully by lead author Michal Samuni-Blank (Israel Institute of Technology), who describes, without mentioning evolution once, how her team discovered and tested the “directed deterrence hypothesis” with chemical analysis and good old field work.



Let’s have some fun with the phrase, “evolutionary conundrum” (pretending, for the moment, that it is not redundant).  So: Wonders of design happen whenever Evolution, the fairy godmother (identified as Tinker Bell), waves her mutation wand with no goal or purpose in mind.  Our mouth receptors were Designed by Evolution to respond to excessive heat, we just learned.  The capsaicin, on the other hand, was Designed by Evolution to turn these receptors on and signal, “Fire in the hole!”  But then, the brains of weird people were Designed by Evolution to fan the flames and make chilis part of their fine cuisine.  The plant was therefore Designed by Evolution to get these weird people to cultivate even more chilis so that they would spread their selfish genes even further.

  • Let’s have some fun with the phrase, “evolutionary conundrum” (pretending, for the moment, that it is not redundant).  So: Wonders of design happen whenever Evolution, the fairy godmother (identified as Tinker Bell), waves her mutation wand with no goal or purpose in mind.  Our mouth receptors were Designed by Evolution to respond to excessive heat, we just learned.  The capsaicin, on the other hand, was Designed by Evolution to turn these receptors on and signal, “Fire in the hole!”  But then, the brains of weird people were Designed by Evolution to fan the flames and make chilis part of their fine cuisine.  The plant was therefore Designed by Evolution to get these weird people to cultivate even more chilis so that they would spread their selfish genes even further.



Watermelon seeds, by contrast, were Designed by Evolution to make humans spit them out.  Humans, in response, were Designed by Evolution to create watermelon seed spitting contests (or was that Evolution designing the watermelon to make the humans do this?).  Evolution designed humans to retaliate by designing seedless watermelons.  (This is known as an evolutionary arms race.)  But if Evolution is such a good Designer, why didn’t Tinker Bell find the mutation to design watermelons with delicious seeds that pass through the human digestive tract?  Oh, we get it; it’s because Evolution designed the human to design toilets and sewer systems, so the seeds would never make it to the soil.  But the watermelon has the last laugh, because Evolution designed the human to realize that without propagation by other means than seeds, their favored watermelons would go extinct.

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