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Bellabob

How does evolution explain symbiosis?

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This is often used as "evidence" against evolution by creationists. Obviously we know evolution happened due to multiple evidences and facts, but I have looked this up and none of the sights explained it to my satisfaction. I'm 15, love the science of evolution, and want to understand it more. Plus, almost everyone I know knows I'm an atheist, and they are always challenging me to debates. They know I don't have all the answers, and when I can't answer a question, they take it as some kind of huge victory. This annoys me.

 

How did it happen? If two animals depend on each other for survival, how did they evolve? Were they both already there, and then something happened that made them depend on each other to survive? An example would be the bacteria living in our intestines. They couldn't survive without us. And us without them (I think?).

 

 

 

Your replies are appreciated.

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Mutualisms are likely to, in the main have started as facultative behaviours - i.e. not essential for survival. Examples of this would be like the cleaner shrimp who obtain food by removing parasites from the bodies an mouths of fish http://en.wikipedia..../Cleaner_shrimp - the shrimp can obtain food elsewhere and the fish can live fine with the parasite load, however it is selectively advantageous for them to engage in mutualistic behaviors and so selection favors those individuals predisposed to engage in them.

 

Directional selection can convert a facualtive trait to an obligate trait, as is seen in systems such as termites who rely on their intestinal symbiont to digest the cellulose in wood. http://www.microscop...ll/termite.html It is likely termite ancestors had a broader diet that did not necessitate the digestion of cellulose, but as the faculative mutualism allowed them to, termites with internal symbionts were selectively advantaged, which changed other behavioral traits (e.g. nesting in wood) that relied upon the mutualism until eventually then termite was unable to function in the absence of the symbiont.

 

http://science.howst.../symbiosis2.htm

Edited by Arete

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This is often used as "evidence" against evolution by creationists. Obviously we know evolution happened due to multiple evidences and facts, but I have looked this up and none of the sights explained it to my satisfaction. I'm 15, love the science of evolution, and want to understand it more. Plus, almost everyone I know knows I'm an atheist, and they are always challenging me to debates. They know I don't have all the answers, and when I can't answer a question, they take it as some kind of huge victory. This annoys me.

 

How did it happen? If two animals depend on each other for survival, how did they evolve? Were they both already there, and then something happened that made them depend on each other to survive? An example would be the bacteria living in our intestines. They couldn't survive without us. And us without them (I think?).

 

 

 

Your replies are appreciated.

 

Some species evolve in response to each other. Like with tube worms, only the ones that could harness that bacterium they host happened to survive, and only the bacterium that could get nutrients from that animal happened to survive.

Edited by questionposter

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As Arete said. Mutualism for starters. Nutrient exchange then may prove beneficial and becomes a conserved trait, whereas other abilities may become lost (as there is no selective pressure to maintain them, for instance). The end result can be an interdependence.

 

Many intestinal bacteria can survive outside of the gut, though they tend to be rather bad as competing with other bacteria.

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hello!

 

I am sorry to ask this here maybe is not totally relevant... but do anyone know about a mutualist symbiosis related with memory ?

 

Lets say an animal with very few memory being guided by other animal or something...

 

 

Thanks!

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That would be very very odd.

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so there is nothing like that right?

 

would be very interesting, i don't know why I had the impression of fish being guide that way for long distances...

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I believe there are parasites that release chemicals that influence the behaviour of their host but they are parasites and not necessarily simbiotic; Simbiosis implies a mutual benefit between the two, whereas parasitical organisms purpose is for their own gain.

 

http://en.wikipedia.org/wiki/Category:Mind-altering_parasites

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hello!

 

I am sorry to ask this here maybe is not totally relevant... but do anyone know about a mutualist symbiosis related with memory ?

 

Lets say an animal with very few memory being guided by other animal or something...

 

 

Thanks!

 

An example might be humans keeping pets, such as cats and dogs. These animals don't have much memory, or intellectual power. Yet they get guided by humans. A human guides them to food, by putting down feeding bowls for them. And filling the bowls with suitable cat or dog food.

 

Thus the animal benefits from the food. And the human benefits from providing the food - because the human gets a good benevolent feeling by watching the pet enjoying its food.

 

So the pet's stomach gets fed. And the human's ego gets fed. Mutual benefit to both parties. Isn't that symbiosis? Although, on a different plane to what you're thinking about, erika. We humans rip up Nature's crude rule-books.

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I do not really see any connection to memory. However, the domestication of other animals was most likely utilitarian in nature, depending on the animal it would be symbiotic, though in other cases much less so.

The enjoyment of companionship however, is part of our nature. Nature's rule book (if you will) is extremely flexible and much more complex than we can imagine.

 

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hello!

 

I am sorry to ask this here maybe is not totally relevant... but do anyone know about a mutualist symbiosis related with memory ?

 

Lets say an animal with very few memory being guided by other animal or something...

 

 

Thanks!

The Honeyguide?

Not so much about memory but the bird has knowledge of where the honeycomb is and imparts that knowledge to other species - honeybears and humans.

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This is often used as "evidence" against evolution by creationists. Obviously we know evolution happened due to multiple evidences and facts, but I have looked this up and none of the sights explained it to my satisfaction. I'm 15, love the science of evolution, and want to understand it more. Plus, almost everyone I know knows I'm an atheist, and they are always challenging me to debates. They know I don't have all the answers, and when I can't answer a question, they take it as some kind of huge victory. This annoys me.

 

How did it happen? If two animals depend on each other for survival, how did they evolve? Were they both already there, and then something happened that made them depend on each other to survive? An example would be the bacteria living in our intestines. They couldn't survive without us. And us without them (I think?).

 

 

 

Your replies are appreciated.

 

 

One of my favorite examples of symbiosis is certain organisms that live with sea anemones and sometimes stony corals, several species of shrimp, crabs, and fish do this to varying degrees. Some do it only as young and as they mature they cease to associate with anemones others cannot live with out the anemone and even lay their eggs in the protective area of the anemone. To some extent this is a chemically learned behavior, when switching to a new host anemone the fish has to slowly acclimate it's self to the new species of anemone or get eaten just like any other fish...

Edited by Moontanman

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Bellabob,

 

The basic answer to your question is that two organisms, both fully functional on their own, were more apt to survive and breed more offspring when their mutually beneficial traits were present, than when they were not. Both organisms then evolved to the point where they were fully dependent on each other. The other answer is that symbiosis is a general term. Some organisms seem to get along just fine without their symbiote, some die without them.

 

Our own mitochondria are descendant from a bacteria that entered early eukaryotic cells (likely either as an invader. . .or as lunch) and helped those cells outperform all rivals. It’s called endosymbiosis. Their closest living relative is the same critter that causes typhus. We certainly couldn’t survive without them and they no longer have the ability. . .with just 37 bacterial genes. . .to live independently outside the cell. Their DNA is not really human DNA.

 

They barely resemble their original antecedent bacterium any more than we resemble the single-celled protoanimal that started this whole thing. We’ve both come a long way, since then.

 

Hope this helps.

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