Definition Of Species, Again.

[Vexer]

I’m dunno about biology, but I’d like to. (Actually I did Bio 101 at Uni, and just Passed) But what I’ve learned about inter-species breeding has confused me. What I'd been taught seems to be Wrong. I’ve read that creatures with different DNA, different Species, have bred viable offspring. Birds, even. And other examples.

 

 

 

Here’s some blah-blah, for those who like it:

 

“… species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring.

 

While in many cases this definition is adequate, the difficulty of defining species is known as the species problem. Differing measures are often used, such as similarity of DNA, morphology or ecological niche.”

 

 

“(the) Presence of specific locally adapted traits may further subdivide species into "infraspecific taxa" such as subspecies (and in botany other taxa are used, such as varieties, subvarieties, and formae).”

 

“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 just which particular species an organism belongs to, because reproductively isolated groups may not be readily recognizable. Another challenge is deciding when to recognize a new species, for example when new data indicate that one previously described species actually may include two or more separately evolving groups, each of which could possibly be recognized as a separate species.”

 

 

End of blah-blah.

 

 

No, wait, there’s more:

 

“Disagreements and confusion happen over just what the best criteria are for identifying new species. In 1942 Ernst Mayr wrote that because biologists have different ways of identifying species, they actually have different species concepts. Mayr listed five different species concepts, and since then many more have been added.] The question of which species concept is best has occupied many printed pages and many hours of discussion."

 

 

Disagreements and confusion.

 

 

Question: if two different ‘species’ can breed viable offspring, are they actually different species, even if their DNA is different?

 

What does ‘species’ mean, then?

[Eclogite]

Here is the problem that I suspect you and many other are suffering from. Species is an artificial construct emerging from the human need for and skill at classifying.

 

There undoubtedly are organisms which are so distinct as to have no possibility of successfully interbreeding. Indeed this is true of most 'species' that we might compare. But if the separation in time, geography and genetic structure is small, then inter-breeding may well proceed. This - in my view - is only a problem if we choose to make it one.

 

Now I have not read Mayr's list of different species concepts, but I am quietly confident that what it will show is that each concept addresses a different classification need. Classification is carried out to simplify; to make the universe more manageable. Biologists, genetecists, palaeontologists, etc all have different end goals, and very likely different methdologies for determining species. So what?

 

I'm reminded of the story about Eric Clapton, told by Jack Bruce, of their days together in Cream. Bruce said, "Of course, we were playing jazz, but we never told Eric, because he didn't like jazz." That's classification for you.