Err, no, this isn\’t how evolution works

But now the annual slaughter, begun in 1967 after a local boy was bitten by an Eastern Diamondback rattlesnake (he survived), is to become “a humane event that celebrates these great native animals”. Snakes are to be borrowed from zoos, instead of hunted down, and, say organisers, the celebration will focus on “educating people about wildlife” and conserving it.

One reason for the change of heart is that the snakes have become increasingly rare, through losing their habitat, getting run over – and being rounded up for the festivals. So great has been the threat from hunting that non-rattling rattlers have been evolving, because they are less likely to be noticed.

Non-rattling rattlers existed before the festival, before the slaughter. So they have not evolved in response to said festival.

There might though be more of them as a portion of the local rattler population, this is true. But this is not evolution, this is selection. The winnowing of evolved forms through the various pressures upon such evolved forms.

The festival has not changed evolution, it has changed the pressures of natural selection.

12 comments on “Err, no, this isn\’t how evolution works

  1. I don’t think anyone said that “this festival has changed evolution”.

    A more correct statement would always be that “the population is evolving” – individuals never do, of course – Lamarck was wrong – or that “the festival has changed the evolutionary pressures”.

    But 45 years is on the order of 15 to 20 rattler generations – with a stark enough habitat change, that’s probably going to produce quite a significant difference in the population, particularly if the genotype already had the relevant mutations in a decent %age of the source stock.

  2. I’m all in favour of real-time demonstrations of natural selection in places well-stocked with religious extremists.

  3. I’m fairly in favour of enthusiastic forms of un-natural deselection in places well-stocked with religious extremists.

  4. Reminds me of a spoof evolution story I saw once, stinging nettles and man are in an evolutionary arms race, we chop them down and they get better stings to combat that. In a few thousand generations they will have evolved to the point where they are more deadly than Cobras.

  5. Bit nitpicky, this. Teleological language is commonplace discussing evolution, because it tends to be more efficient than being accurate. You know, “everything in Grimthorpe is covered in coal dust, so black finches evolved” kind of thing.

  6. @Ian B

    Teleogical language is very commonplace when discussing evolution, because it’s efficient shorthand. But it causes much confusion. In fact, it’s probably the reason most people don’t understand evolution.

    Is there any evidence that the non-rattling is transmissible? Or are they just killing the ones that rattle? In which case they are changing the population structure but not actually causing selective pressure.

  7. In which case they are changing the population structure but not actually causing selective pressure.

    Eh? Being killed by a predator for rattling is a pretty strong selective pressure, is it not?

    Anyway, most people don’t have a deep understanding of evolutionary theory for the same reason they don’t understand economics, quantum mechanics, how a steam pressure reducing valve works or programming in C++. They’re too busy with other stuff that is in their opinion more useful to them.

  8. It may be that as the rattle grows larger as the snake itself grows and young ones have a reduced ability to produce the sound that it’s the older, larger ones that are getting killed thus biasing the population towards young snakes, which would also account, in part, for their decline. I’m not sure if that would have any evolutionary effects though. Here’s a good description of the creatures
    .http://cdri.org/nature-notes/animals/herps/rattlesnake-rattles/

    There’s a reference there to a rattleless rattlesnake although it doesn’t name the species. here’s a sceptical take, http://urbanlegends.about.com/od/snakes/a/Rattlesnakes-Not-Rattling.htm

  9. But if the rattling/non-rattling isn’t hereditary then killing the rattling rattlers doesn’t introduce selective pressure. If it is, then it does.

    It’s true that most people have better things to do than study the finer points of evolutionary theory and genetics, but unlike, say, the steam governor, quantum mechanics and C++, that doesn’t stop them talking about it. Economics also attracts a lot of ‘experts’ of that kind (guilty, m’lud).

  10. I suppose there could be selective pressure happening as well as population change, it would be interesting to know more about that non-rattler, what is producing its drift towards rattlelessness ( I like the sibilants, seems appropriate ) ? I can’t find a reference though. Anyway I’ll shut up now as I definitely come under the heading of people who know little rattling on.

  11. Well, the presumption in the article is that Rattlesnakes without rattles are becoming more commonplace. If they are mutants, then this is evolution via natural selection. Rattling is reducing the fitness of rattlers versus non-rattlers in the presence of a predator (humans).

    So anyway, I’m presuming the non-rattling is hereditary.

  12. When young, I had experience handling snakes of many kinds, including rattlers, and, also, of catching several species, chiefly the Western Diamondback and Prairie Rattler. Some species are more inclined to rattle than others and even various individuals of the same species may vary widely in their tendency to rattle (and under what circumstances). Nor is the “rattling” vibration of the tail confined to rattlesnakes but is a widespread phenomenon generally related to nervousness (and may even produce a sound
    slightly akin if the vibration occurs in dry vegetation). It’s definitely a “fear” response (and will almost never occur when tracking or confronting prey).

    Rattlesnakes vary significantly by species in their propensity to rattle. Timber rattlers (and their relative, the Canebreak, often have to be
    quite provoked. Eastern Diamondbacks usually rattle, Western Diamondbacks and Prairies almost always. The U.S. is home to somewhat over 50 species with great variation in the rattling tendency. These range in adult size from barely 2 feet (Pygmy Rattlers and Massasaugas)
    to the Diamondbacks , with large Westerns going 6-1/2 feet (and 6-7 lbs) and large Easterns about the same length (and nearly double the weight). The “baddest” is the Eastern but the Western manages to be the one responsible for more bites (and deaths) by virtue of great range and significantly more intimate contact with human populations over that range.

    A very dangerous rattler–known as the “cascabel” or “cascavel” (meaning “rattler”) is found from Mexico thru most of northern South America.

    Many non-venomous snakes have the same nervous “rattling” response to disturbance. And in one genus (Angkistrodon) found in the US, Mexico, and NE Asia (including Japan) which includes the water moccasin, the copperhead, the cantil, and mamushi), the young are born alive and equipped with a bright yellow tail; all of them use the tail, sometime with slight twitches or wiggles (and sometimes rapidly whirring–like a rattler), to attract small prey (sometimes even in water to catch small fish or frogs).

    Baby rattlers are born alive, with a button-like end of the tail and add a segment at each shedding of the skin. But many have lost some of these segments (and the button) by the time they reach adulthood; anything beyond 6-8 segments is highly likely to be broken and lost in the ordinary course of their existence.

    I’ve had three bites–only one serious. And, once, a big (over 6′) Western managed to bite thru the toe of a very stout pair of high boots I was wearing. One fang broke off in the leather but the other managed to make a good scratch on my big toenail.

    A great deal of my hunting of rattlers was done near the town of Cotulla, in Texas (that’s where LBJ taught school when young) on the Nueces River. I operated with a local guy and our chief method was patrolling dirt roads on large “spreads,” seeking the tell-tale “drags” where they’d crossed the road, from which point we’d continue to track them down.

    I have an old friend (88 yrs old) whose father was Snake King (legally awarded by a court against a claimant who’d disputed and infringed his right to the name. Case decided via catching, bagging, and crating contest spanning 12 hours)
    I spoke with him by phone just a few days ago. He became a circus lion-tamer at eight and reached his height at 13 (in which year he did
    command performances for the Q of E and was also billed above Bob Hope in Atlantic City). He had a lion in his act for each year of his age.

    If anyone would like to know what a really bad bite is like, an account of Marlon Perkins’ bite by a Gaboon Viper is in the book REPTILES OF THE WORLD by Raymond L. Ditmars. Another is a series of photographs of a friend’s grandson who was bitten by a Western Diamondback at night while walking (barefoot!) home through a brushy lot from a swimming pool. He was in the hospital for 2 or 3 weeks and required about a dozen surgeries to repair damage (he’d been bitten on the top of one foot.

Leave a Reply

Name and email are required. Your email address will not be published.