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Author Topic:   [Almost] Convergent Evolution?
Tupinambis
Junior Member (Idle past 4655 days)
Posts: 18
Joined: 12-12-2010


Message 1 of 12 (596045)
12-12-2010 2:15 PM


The Monitor Lizards (Varanus) and the large Tegus of South America (Tupinambis) are sometimes cited as being examples of convergent evolution. The beaded lizards aside there are no true monitor lizards in the new world so it is widely believed that the whiptails (small, skink-like lizards) adapted to take over the niche of large-carnivorous lizard.
This is particularly important when comparing their respective ecologies: the Nile Monitor is the dominant predator of Nile Crocodile nests while the Common Tegu is the dominant predator of caiman eggs. Both also apparently exhibit exceptional physical endurance for reptiles, although I personally can't testify to that from observation.
There seem to be HUGE differences in human interactions however; as in monitors make lousy pets while certain Tegus (Red and Argentinian Black and White) are terrific by most standards. Is there any real explanation as to why some of the Tegu are much more sociable with humans while the monitors are not? I should point out that the Arg B&W Tegu is an omnivore and the Red is an herbivore. Almost all of the monitors (the ones kept as pets anyway) are strictly carnivorous as is the Common Tegu (which is equally as unsociable).
I seriously doubt that their diet has any real bearing on their attitude: Iguanas are strict herbivores and they can be just as ill-mannered as the monitors.
Obviously these lizards didn't evolve to be sociable with people and they certainly didn't have captivity in mind. However, neither did the monitors outside of Africa or the Iguanas/ Does anyone here have any ideas as to how sociability in these lizards could have first developed or why it was preferential to their survival? And what do you think of the possibility of true, legitimate animal domestication among reptiles?
In truth the "False Monitor" (Tejvaranus/Callopistes flavipunctatus) is a far better example of convergent evolution because it actually looks like a monitor as an adult. The actual Tegus, in my opinion, only look like monitors as babies (my avatar). Both the False Monitor and the Tegus are very closely related though, so the point remains.

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Admin
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Message 2 of 12 (596114)
12-13-2010 8:42 AM
Reply to: Message 1 by Tupinambis
12-12-2010 2:15 PM


How does this example of convergent evolution tie in to the creation/evolution debate?

--Percy
EvC Forum Director

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Tupinambis
Junior Member (Idle past 4655 days)
Posts: 18
Joined: 12-12-2010


Message 3 of 12 (596118)
12-13-2010 10:21 AM


EvC?
This topic in of itself doesn't have much to do with an Evolution/Creationism controversy since to really answer the question, one must already assume evolution to be true. This would be something for one of the less relevant sections, like coffee house I guess.

  
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Message 4 of 12 (596122)
12-13-2010 10:38 AM


Thread Moved from Proposed New Topics Forum
Thread moved here from the Proposed New Topics forum.

  
Just being real
Member (Idle past 3936 days)
Posts: 369
Joined: 08-26-2010


Message 5 of 12 (596275)
12-14-2010 7:22 AM
Reply to: Message 1 by Tupinambis
12-12-2010 2:15 PM


Is there any real explanation as to why some of the Tegu are much more sociable with humans while the monitors are not?
Sorry, my entire knowledge of lizards could fit in a thimble, and I know squat about their behavior developments. However my attention was caught by your bringing up convergent evolution. This is a subject that I have always been curious about. For others who are not familiar with the term, it is the idea that very similar traits developed into two completely unrelated organisms. For example the bat wing and the bird wing are said to be convergent evolutionary traits. Likewise are the eyes and many other organs found in unrelated organisms.
My question is how could two completely unrelated species, like your lizards, develop such similar traits? Or for another example, on the continent of Australia, the Tasmanian Wolf (now extinct) was every bit as much of a "wolf" as the North American Timber Wolf, with the exception it was marsupial. Yet the super continent is said to have broken up long before the arrival of this Australian species. So if it evolved on this isolated continent, which has no other indigenous dogs, what family did it evolve from?
I mean suppose the genome of a species has about a million sites where a change of a single nucleotide could yield an advantage by natural selection. And these sites are spread through some ten thousand genes that each encode some ten thousand proteins. So there would have to be a hundred potential adaptive changes that could occur in each of ten thousand genes. This all means that any given species must have a lot of freedom in the way it evolves.
Say it takes roughly 500 steps to lead to a new species. This would mean that in the first step there would be a million choices. After one occurred, there would then be a million choices in the next step, and in the third step and so on. If this occurred for the entire 500 steps, the process would have enormous freedom. If we were to start the process over (and the mutations are random), then the odds against it repeating the exact same path are a million times itself 500 times.
My point is that if the mutations are truly random, and if at each step there are a million choices, then the chances of the same trait evolving twice should be impossible.

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bluegenes
Member (Idle past 2477 days)
Posts: 3119
From: U.K.
Joined: 01-24-2007


Message 6 of 12 (596276)
12-14-2010 7:31 AM
Reply to: Message 5 by Just being real
12-14-2010 7:22 AM


Just being real writes:
My point is that if the mutations are truly random, and if at each step there are a million choices, then the chances of the same trait evolving twice should be impossible.
A quick couple of points, because we're not really on topic.
Natural selection isn't random, and organisms developing similar traits can be in similar situations in relation to their environments.
Convergent evolution isn't parallel evolution. The similar characteristics are not arrived at by the same genetic route.

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Just being real
Member (Idle past 3936 days)
Posts: 369
Joined: 08-26-2010


Message 7 of 12 (596278)
12-14-2010 8:31 AM
Reply to: Message 6 by bluegenes
12-14-2010 7:31 AM


Natural selection isn't random,
No but the mutations are (supposedly).
organisms developing similar traits can be in similar situations in relation to their environments. Convergent evolution isn't parallel evolution. The similar characteristics are not arrived at by the same genetic route.
I see.
So if you and I both went to the train station (though we are starting from two different cities), and randomly started picking locations of travel, even though we both experienced the same weather and financial obligations etc... you are saying the likelihood is that with a million different choices at each rout that with in five hundred trips we would eventually both wind up at the same station, just by different routs?

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frako
Member (Idle past 305 days)
Posts: 2932
From: slovenija
Joined: 09-04-2010


Message 8 of 12 (596280)
12-14-2010 8:37 AM
Reply to: Message 7 by Just being real
12-14-2010 8:31 AM


So if you and I both went to the train station (though we are starting from two different cities), and randomly started picking locations of travel, even though we both experienced the same weather and financial obligations etc... you are saying the likelihood is that with a million different choices at each rout that with in five hundred trips we would eventually both wind up at the same station, just by different routs?
Lets say getting of and on at a tain station is mutation. You also haveto include natural selection and lets say the proximity to station x is selected for.
So we both get up on a train if we get off on any platform that is further from platform x we are selected against so we start over at the last platform we have been on. Using this process we would both eventually arrive at the platform x

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bluegenes
Member (Idle past 2477 days)
Posts: 3119
From: U.K.
Joined: 01-24-2007


Message 9 of 12 (596282)
12-14-2010 8:53 AM
Reply to: Message 7 by Just being real
12-14-2010 8:31 AM


Just being real writes:
I see.
So if you and I both went to the train station (though we are starting from two different cities), and randomly started picking locations of travel, even though we both experienced the same weather and financial obligations etc... you are saying the likelihood is that with a million different choices at each rout that with in five hundred trips we would eventually both wind up at the same station, just by different routs?
No, you don't see. Where's natural selection in your analogy?
Here's a better one. Two human cultures invent the bow and arrows separately. Why? Because it is advantageous. The bows and arrows are similar in shape and appearance. Why? Because of the physical restrictions on how they can work effectively. The environment. That's convergent invention.
Wolves and Tasmanian tigers evolved to fill similar niches. It is convergent evolution, not parallel. It is not a single route of mutations that can produce a wolf-like form. Their non-wolf-like ancestors were different, so they are like two groups starting off at different stations and going along zig-zag routes with an advantage for them in every stop on the route, and then ending up at adjacent stations in the same city, where they collect million dollar rewards.
The story of the lizards in the O.P. would be similar. They fill similar niches on different continents.
Edited by bluegenes, : No reason given.

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nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 10 of 12 (596299)
12-14-2010 9:41 AM
Reply to: Message 7 by Just being real
12-14-2010 8:31 AM


Just being real writes:
So if you and I both went to the train station (though we are starting from two different cities), and randomly started picking locations of travel, even though we both experienced the same weather and financial obligations etc... you are saying the likelihood is that with a million different choices at each rout that with in five hundred trips we would eventually both wind up at the same station, just by different routs?
No, he is saying that you might both have similarly interesting vacations, and interesting for similar reasons, even though you took your vacation trips to different places. We might call that "convergent vacationing experiences".

Jesus was a liberal hippie

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Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 11 of 12 (596321)
12-14-2010 11:09 AM
Reply to: Message 5 by Just being real
12-14-2010 7:22 AM


I mean suppose the genome of a species has about a million sites where a change of a single nucleotide could yield an advantage by natural selection. And these sites are spread through some ten thousand genes that each encode some ten thousand proteins. So there would have to be a hundred potential adaptive changes that could occur in each of ten thousand genes. This all means that any given species must have a lot of freedom in the way it evolves.
Not that much, because you're ignoring natural selection.
I recently wrote a computer program where what evolves are two-dimensional shapes. The selective criterion was maximizing area divided by perimeter.
Each time I ran the program, the initial shape was random, the mutations were random ... but the end result was always a perfect circle. Because the selective pressures were not random and were the same in every case, every simulated population converged to exactly the same shape. This is not surprising or unlikely; it is inevitable.
Really, if you can't figure out this sort of thing on your own you need to get an introductory text on evolution and start again from the beginning.

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Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 12 of 12 (596325)
12-14-2010 11:17 AM
Reply to: Message 1 by Tupinambis
12-12-2010 2:15 PM


Is there any real explanation as to why some of the Tegu are much more sociable with humans while the monitors are not?
I shouldn't think so. The property of being or not being domesticable would not have been selected for, so I guess it's just one of those things.
There are differences like this even in closely related species. Horses are domesticable but zebras are downright dangerous; the llama has been domesticated but no-one can domesticate the vicua, despite the fact that there'd be a lot of money in it for anyone who could (its wool is much sought after).

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