Saturday, August 01, 2015

Evolutionary biogeography

A familiar challenge to flood geology is how the animals surmounted natural barriers to repopulate the post-diluvian planet. That's not a problem for local flood interpreters. 

If, however, this poses a problem for flood geology, it poses a similar problem for evolutionary biogeography. Let's take a concrete case: the coral snake. They belong to the Elapid family. Most species or subspecies inhabit the Old World (e.g. Asia), but we also have them in the New World (the SE and gulf coast).

But if they originated in the Old World, how did they get here? They didn't swim.  

1. One traditional explanation is vicariance, as Pangea broke up. 

i) However, I believe that would require Elapids to evolve prior to the breakup. Although Darwinians think snakes are ancient, they think venomous snakes are more recent. Constrictors are the most primitive snake. The Ur-snake.  

So does vicariance fit the evolutionary timeframe, according to evolutionary geology and biology? Can that be coordinated?

ii) But another complication is the relationship between the eastern coral snake and the scarlet king snake. Didn't the scarlet king snake have to evolve or adapt after the coral snake in order to mimic its markings? 

So either both originated in the Old World, or the coral snake originated in the Old World while the scarlet king snake is descended from a New World ancestor. That also complicates the evolutionary synchrony, does it not?

2. Another mechanism for biogeography is dispersal. Here's a definition: Either a population can slowly expand from the margins of its geographical range or a small number of individuals can disperse to a new location some distance from the current edge of the species range, or a combination of both of these processes can occur. 
Here's an exposition:
Various dispersal routes might have been followed in the biogeographic history of a species. 
• Corridors 
Two places are joined by a corridor if they are part of the same land mass: Georgia and Texas, for example. Animals can move easily along a corridor and any two place joined by a corridor will have a high degree of faunal similarity. 
• Filter bridges 
A filter bridge is a more selective connexion between two places, and only some kinds of animals will manage to pass over it. For instance, when the Bering Strait was above water, mammals moved from North America to Asia and vice versa, but no South American mammals moved to Asia and no Asian species moved to South America. The reason is presumably that the land bridges at Alaska and Panama were so far apart, so narrow, and so different in ecology that no species managed to disperse across them. 
• Sweepstakes 
Finally, sweepstakes routes are hazardous or accidental dispersal mechanisms by which animals move from place to place. The standard examples are island hopping and natural rafts. Many land vertebrates live in the Caribbean Islands, and (if their biogeography is correctly explained by dispersal) they might have moved from one island to other, perhaps being carried on a log or some other sort of raft.
Applied to the issue at hand, that would involve a horseshoe journey of many thousands of miles from a tropical and/or subtropical zone in the S. hemisphere of the Old World up to the Bearing land bridge, just south of the Arctic Circle, then all the way down to a tropical/sub-tropical zone of the New World. Raises lots of logistical issues:

i) Do snakes cross ecological zones? Aren't they adapted to a particular climate?

ii) Do snake populations migrate thousands of miles?

iii) Would there be enough food along the way?

iv) Apropos (i), is it just incidental that some snake species cluster in the tropics/subtropics while others cluster in the temperate zone? To take a comparison, why are there rattlesnakes in the SW and Eastern Washington, but not in Western Washington? Surely climate is the differential factor.

But if dispersion is a viable mechanism, and they are fairly indifferent to the climatic difference, why aren't there rattlesnakes in Western Washington? 

i) Surely the dispersion of rattlesnakes from the SW to Western Washington would be orders of magnitude easier than the dispersion of coral snakes from, say, India to the SE, a continent away, via a Bering land bridge. 

ii) Also, didn't the postulated Bering land bridge only exist during the last Ice Age, when sea levels were lower? But even if tropical snakes can survive in the temperate zone, how could they survive in the arctic zone? 

iii) Many exotic snake collectors living in the temperate zone. Every so often one of their snakes (native to the desert, tropics or subtropics) escapes. To my knowledge, these have not become established–unlike Florida! 

If, however, objections notwithstanding, dispersal is the mechanism which accounts to the presence of coral snakes in the Americas, that explanation is available to flood geologists as well as Darwinism. 

3. I suppose, if they got sufficiently desperate, Darwinians could postulate convergent evolution.

4. Perhaps a Darwinian could postulate that they got here on downed trees, or something like that. 

5. Or perhaps a Darwinian could postulate that they were introduced into the New World by ancient mariners. Maybe they brought coral snakes along to dip arrow points in the venom. Or maybe they worshipped venomous snakes and brought their "gods" along for the ride.

6. Or maybe the snakes were stowaways. Ships have rats. Where you have rats, that attracts snakes.

However, these explanations (4-6) are available to flood geologists.

7. I suppose one final explanation is that eastern coral snakes derive from seasnakes which reverted to land snakes. Given that contemporary young-earth creationists subscribe to microevolution and adaptation, that explanation is available to flood geologists as well as Darwinians. 

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