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Praeluceo

A questions I can't find a good answer for.

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Someone posed this question to me and it has kind of been bothering me because I cannot find a sufficient answer. The basic question is what standard do we use to classify animals? For instance, if you have 2 birds that look very similar and have similar eating habits, but different coloring, are different sizes, what makes us decide it is a different species or not?

That is the first question. The second question is if mankind are currently all considered homo sapien, why do we not apply the same tools to classify humans as we do animals? (this is based on the understanding that appearence, habits, diet, etc are things factored into establishing a classification of an animal or new species).

The third and last part of this questions is, could or has science come up with a genetic or DNA method of differentiating between animal species and if so is it universally applied to homo sapiens as well?

 

I realize some of this could be pretty controversial and what not, but I have not located a sufficient answer. Thanks for anyone that could point me to some good source material to review.

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Someone posed this question to me and it has kind of been bothering me because I cannot find a sufficient answer. The basic question is what standard do we use to classify animals? For instance, if you have 2 birds that look very similar and have similar eating habits, but different coloring, are different sizes, what makes us decide it is a different species or not?

This is known as the 'species problem'.

 

The species problem is a mixture of difficult related questions that often come up when biologists define the word "species". Definitions are usually based on how individual organisms reproduce, but biological reality means that a definition that works well for some organisms (e.g., birds) will be useless for others (e.g., bacteria).

 

One common, but sometimes difficult, question is how best to decide which species an organism belongs to, because reproductively isolated groups may not be readily recognizable; cryptic species may be present.

 

Another common problem is how to define reproductive isolation, because some separately evolving groups may continue to interbreed to some extent, and it can be a difficult matter to discover whether this hybridization affects the long-term genetic make-up of the groups.

 

Many of the debates on species touch on philosophical issues, such as nominalism and realism, as well as on issues of language and cognition.

 

The current meaning of the phrase "species problem" is quite different from what Charles Darwin and others meant by it during the 19th and early 20th centuries.[2] For Darwin, the species problem was the question of how new species arose: speciation. ...

source: >> Species problem @ Wiki http://en.wikipedia.org/wiki/Species_problem

 

 

That is the first question. The second question is if mankind are currently all considered homo sapien, why do we not apply the same tools to classify humans as we do animals? (this is based on the understanding that appearence, habits, diet, etc are things factored into establishing a classification of an animal or new species).

All Homo sapiens can breed and produce breeding offspring, therefore they are all of one species.

 

The third and last part of this questions is, could or has science come up with a genetic or DNA method of differentiating between animal species and if so is it universally applied to homo sapiens as well?

The work is in progress, but no definitive answers have been forthcoming:

...Genetics

Few speciation genes have been found. They usually involve the reinforcement process of late stages of speciation. In 2008 a speciation gene causing reproductive isolation was reported.[31] It causes hybrid sterility between related subspecies. ...

source: >> Speciation @ Wiki http://en.wikipedia.org/wiki/Speciation

 

 

I realize some of this could be pretty controversial and what not, but I have not located a sufficient answer. Thanks for anyone that could point me to some good source material to review.

It is not controversial unless you have in mind to promote racial discrimination.

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what makes us decide it is a different species or not?

 

 

The basic definition of a species is a population that can interbreed and produce fertile offspring (so, could the birds breed and produce fertile young?). But the definition has blurry boundaries, partly because of the gradual nature of evolution - things change very gradually and two populations will not suddenly be unable to interbreed, it will diminish very slowly. Ring species illustrate the idea very well...

 

http://en.wikipedia.org/wiki/Ring_species

 

Wider classifications are even more arbitrary than the species definition.

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So in the case of lions and tigers, that can breed and make "liger" offspring, they are still differentiated by the fact the offspring are fertile then? And to the contrary, if an offspring was fertile they would be considered the same species?

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So in the case of lions and tigers, that can breed and make "liger" offspring, they are still differentiated by the fact the offspring are fertile then? And to the contrary, if an offspring was fertile they would be considered the same species?

You also have to factor in regularity of interbreeding to some extent. Even if it's theoretically possible for two animal populations to interbreed and have viable offspring, if they never do for behavioral or other reasons, they may be considered separate species.

 

The line between species is often quite blurry and imprecise. These are categories that we're imposing on nature to make sense of it rather than categories that have an independent, "real" existence.

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Like others have said, virtually every level of classification is arbitrary. An analogy one professor I had gave was, "Classification is kind of like incest. Everyone is related, but where's the line where it's weird when you have sex."

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So if adaptation is clearly happening, and genetic mutation is happening too, is it not possible that 2 animals which we currently have as different species are actually the same and have adapted enough and mutated enough under different environments to where they no longer produce fertile offspring? Is there perhaps a genetic mutation distance that is quantifiable that prevents the creation of fertile offspring between what could've been 2 different adaptations of the same species?

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So if adaptation is clearly happening, and genetic mutation is happening too, is it not possible that 2 animals which we currently have as different species are actually the same and have adapted enough and mutated enough under different environments to where they no longer produce fertile offspring? Is there perhaps a genetic mutation distance that is quantifiable that prevents the creation of fertile offspring between what could've been 2 different adaptations of the same species?

 

If two species can definitely not produce fertile offspring they are certainly considered as different species under the current definition. But very similar species have definitely diverged from a single species some relatively short (in evolutionary terms) time ago. It's not possible to quantify a cut off point because change is always gradual - fertility will slowly diminish with divergence.

Nature doesn't really recognise species definition. To try and put things into sharply defined boxes is going against nature to a strong degree, it's better not to try and define so sharply.

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So if adaptation is clearly happening, and genetic mutation is happening too, is it not possible that 2 animals which we currently have as different species are actually the same and have adapted enough and mutated enough under different environments to where they no longer produce fertile offspring? Is there perhaps a genetic mutation distance that is quantifiable that prevents the creation of fertile offspring between what could've been 2 different adaptations of the same species?

Not only is it possible, every species is descended from a common ancestor if you go back far enough. Every major car species was once a single species that branched out into all the current forms. Every species of mammal was once a single species that branched out into all of the various mammals. Every vertebrate was once a single species. Every animal was once a single species. Go back far enough and humans are descended from a population of life that also gave rise to plants.

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Not only is it possible, every species is descended from a common ancestor if you go back far enough. Every major car species was once a single species that branched out into all the current forms. Every species of mammal was once a single species that branched out into all of the various mammals. Every vertebrate was once a single species. Every animal was once a single species. Go back far enough and humans are descended from a population of life that also gave rise to plants.

Which leads to the following, seemingly nonsensical, phrase:

 

To be fair, bananas are like 90% horse.

Edited by Greg H.

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