Darwinian Evolutionary Theory encompasses such tenants as natural selection, survival of the fittest, and environmental adaptation. Simply put, those members of a species who were best equipped to survive whatever environment they faced did so while those less well equipped perished. The survivors then passed on the genetics of whatever adaptation they had been blessed with and the entire species evolved and thrived.
Nature is full of examples.
The bigger, stronger, and faster gazelles avoided becoming cheetah food while the slower ones did not. They passed along their added speed to the next generation. Longer necked giraffes could better reach the tender leaves of certain trees so could survive where those with shorter necks could not. This adaptation was likewise passed along. Snow leopards blessed with a winter white coat avoided predators, while those that didn’t were easy targets. Soon all snow leopards carried that genetic advantage.
These are the basic tenets of evolutionary change.
We see this in medicine on daily basis. Bacteria are constantly adapting to survive the antibiotics that are used against them. Those bacteria who can avoid death by penicillin are free to procreate and pass on this resistance to the next generation. The very deadly infection known as methicillin-resistant staph aureus (MRSA) is an example of this. Staph aureus is a nasty little dude. Infections of the skin, the lungs, and particularly the cardiac valves by these bacteria often prove deadly. Methicillin is a form of penicillin originally designed to attack these very organisms but with time they developed resistance to all penicillins, including Methicillin. This is one of the reasons antibiotics should be taken until completion of the prescription but unfortunately many people feel better after two or three days and stop whatever antibiotic they were prescribed. This allows those bacterial organisms, which might ultimately have been killed, to survive and adapt to the presence of the antibiotic. This is passed on from generation to generation and nasty little bugs like MRSA are created.
So what does all this have to do with religious rites?
It seems that every year the Zoque of Southern Mexico gather at a particular cave known as Cueva del Azufre for an annual ritual. The cave is inhabited by molly fish. A portion of the ritual is to impregnate the water of the cave with the mashed root of the Barbasco plant. This root contains a powerful anesthetic that stuns the fish so that they can then be used in the religious ritual.
A recent study by Mark Tobler of Texas A&M University showed that over time the fish in this cave have become more resistant to the anesthetic toxin. They have adapted to the traditions and religious practices of the Zoque. Not consciously of course, but from the fishes’ point of view the drug is an environmental stress that has resulted in some change in the biochemistry of the species so that they can survive in this altered environment. This adaptation has been passed from generation to generation.
The irony of a religious rite promoting evolutionary change is thick to say the least.
The Crime Fiction Writer's Blog 
Heather
October 8, 2010 at 7:00 am
Interesting!
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Brenda
October 8, 2010 at 1:41 pm
Your blog is always unique and interesting. Wow.
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D.P. Lyle, MD
October 8, 2010 at 6:41 pm
Thanks. I try to have fun with it.
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Jeannine
October 8, 2010 at 3:34 pm
You are confusing microevolution and macroevolution. The word evolution means “Change over time”. Microevolution is change over time within a species. The vast majority of religious people have no problem with this idea. Macroevolution is change between species. This is the fish becomes a bird idea. That is what religious people and many scientists have problems with. What you have referenced shows an example of microevolution so there is no irony involved unless of course the fish suddenly grow wings and fly away.
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D.P. Lyle, MD
October 8, 2010 at 6:37 pm
Not really. Micro leads to macro and macro always begins micro. Evolutionary changes are always small since a large change either would be so dramatic as to be deadly or so large that there could not be a genetic basis for the change. If these fish were exposed to this toxin every day for many centuries they would first expand an existing enzymatic system to handle it–which is likely the case here–and then perhaps develop a secondary enzyme system that was better or more efficient and so on. At some point these enzymatic system changes might lead to actual physical changes–maybe a larger adrenal gland or pancreas or whatever–and this in turn could lead to some other survival advantage-maybe the larger gland produces some other protein that led to greater musculature, faster swimming for better escape and food gathering—and so on. You get the idea. One small change leads to another and so on. Fish didn’t become amphibians one day–it took millions of years and thousands of small changes—and then evolving from amphibians to land based animals followed the same process. So micro leads to macro and macro springs from a series of micro changes. These changes aren’t between species but rather within the species that ultimately leads to a new species.
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Carola
October 8, 2010 at 7:15 pm
Interesting to speculate that religious beliefs may have led to evolutionary changes in the human brain.
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Steve Kelner
October 8, 2010 at 7:25 pm
Interesting post, and I quite agree with the irony of a religiously produced evolution, but there’s one nuance I would add. Evolutionary fitness is not limited to those who are best-equipped to survive — a common misunderstanding — it’s those who have the most progeny survive to reproduce. A strain of creature that dies young but produces scores of descendants (who then survive to reproduce) is more successful in evolutionary terms than one that survives to 300 years old but has one descendant.
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D.P. Lyle, MD
October 9, 2010 at 6:00 am
You are correct. Of course those that do produce in massive numbers are usually food items for some predator or at least something further up the food chain.
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Steve Kelner
October 9, 2010 at 6:57 pm
Not quite what I meant, I’m afraid. Evolution doesn’t require massive numbers; any differentiation in reproductive success will introduce an evolutionary difference over sufficient time. This is true at any point on the food chain. I was just using a more obvious comparison.
Fitness as Darwin defined it is reproductive success — differences in reproducing progeny. Everything else — being stronger, smarter, faster — merely contributes to evolutionary fitness, it is not fitness in itself. In fact, many species have been tremendously strong, smart, fast, etc. in their environment, but when that environment changed they either evolved or died out. Witness the dinosaurs, who were well-adapted to their environment and far more successful than mammals in that environment, until it was radically changed by an meteorite!
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D.P. Lyle, MD
October 9, 2010 at 7:23 pm
Very true. But cheetas developed speed to give them a survival advantage for their environment and food source. And yes a meteor could take them out too but that would not be due to an evolutionary disadvantage but rather a cosmic accident. The point of the original post is that I find it interesting and ironic that a religious ritual forced a group of fish to adapt and apparently pass that adaptation on to their offspring.
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gkparker
October 13, 2010 at 1:11 pm
I watched an interesting show the other night mainly about some of the bizarre shapes dinosaurs came in and what purpose those might have served. Some that we used to think were for protection in fact turn out not to be very good for that. Instead, they said the shapes were on par with the colorful, but totally useless feather displays a lot of birds have — it’s all part of the mating ritual.
They postulated that giraffes may have been the same. They do use their necks in their mating ritual. The males ‘spar’ with their necks and head, slapping their necks together and banging heads. Thus the giraffe with the strongest, longest neck got the best females so the trait was magnified. It would also have given them access to leaves high up, but since most animals get along just find with short necks this might not be the real reason. After all, that brilliant display the male cardinal or paradise bird displays could actually be seen as a disadvantage since it gives predators an easier target but still it persists so it must be successful. And I think it’s been demonstrated that the brightest or showiest bird gets the choice territory or mate.
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D.P. Lyle, MD
October 13, 2010 at 10:17 pm
Good stuff. Thanks for sharing.
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