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Author Topic: How are species determaned?  (Read 2473 times)

Offline Eric A. Taylor

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How are species determaned?
« on: 06/11/2009 09:10:09 »
All breeds of dogs are considered to be the same species (Canis lupus familiaris a subspecies of the wolf Canis lupus) despite a wide verity of body forms and behavior. Some breeds cannot even interbreed (though probably for practical, rather than genetic reasons. Say trying to breed a Great Dane with a Chihuahua.)

Now take two different species of snake say the Sonora and Mojave sidewinders (Crotalus cerastes cercobombus and Crotalus cerastes cerastes respectively) Two snakes with very bad attitudes and the venom to back up their attitudes, who look and behave very much alike and they are considered different species. When I worked at Grand Canyon National Park there were two species of squirrel that lived on the north and south rims, only 10 miles apart but separated by an impassible (for the squirrls) canyon. They did look a little different.
 
Is it because dogs are a human created species that they are divided by breeds?


 

Offline Nizzle

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How are species determaned?
« Reply #1 on: 06/11/2009 12:09:12 »
(Crotalus cerastes cercobombus and Crotalus cerastes cerastes respectively)

This looks to me like being the same species, ie Crotalus cerastes.. no? with cercobombus and cerastes at subspecies level.

Anyway, where to draw the line between species is still not exact science, but lately more and more efforts are made to postulate a "definition of a species". This involves evolutionary genetics and % of genomes that are identical.
 

Offline hwobot

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How are species determaned?
« Reply #2 on: 06/11/2009 13:16:16 »
I always thought different species meant they couldn't reproduce with each other. But then again, dogs can crossbreed so I suppose my explanation is too simplistic.
 

Offline Nizzle

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How are species determaned?
« Reply #3 on: 06/11/2009 14:18:01 »
a donkey and a horse are different species, but they can reproduce.
Their offspring is always sterile though.

This has been a 'definition' of a species in the past, but as you might suspect, when entering the bacterial/viral world, this was no longer an adequate 'definition' of a species...
 

Offline Madidus_Scientia

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How are species determaned?
« Reply #4 on: 06/11/2009 14:29:49 »
As different as our different breeds of dogs look, genetically they are still similar enough to interbreed, which is why they are considered the same species. The morphological differences between them aren't actually that significant, genetically.

Quote
Is it because dogs are a human created species that they are divided by breeds?

I would say so yes, it was our influence that selected for/against certain traits that resulted in the many different types of canine, in a rather short space of time (in terms of evolution). The humans who decided which dogs to breed placed such a strong selective pressure on appearance, much more than any other traits. This is perhaps why our different breeds do not yet differ enough genetically to become a different species, although they look vastly different. Since it was the humans who provided them with their food and safety etc., other traits hardly mattered.
« Last Edit: 06/11/2009 14:31:27 by Madidus_Scientia »
 

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How are species determaned?
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