Definition of species under attack?

[nomadreid]

I learned that two sexual organisms are considered different species when no two organisms having their respective DNA structures could interbreed to produce viable offspring. Put another way, when looking it up, I find the definition:

A single evolutionary lineage of organisms within which genes can be shared, and that maintains its integrity with respect to other lineages through both time and space.

But then I read that:
(a) Neanderthal interbred with homo sapiens to give part of today's modern man
(b) Neanderthals is a different species from homo sapiens.
Hence, the above definitions don't seem to hold. Can someone correct these definitions in light of this?

 

[atyy]

Wikipedia indicates that this discussion might be useful
http://www.pnas.org/content/96/13/7117.long

More tangentrially, the extent to which the "biological species concept" is useful is discussed in these articles.
http://www.ncbi.nlm.nih.gov/pubmed/9533126
http://www.ncbi.nlm.nih.gov/pubmed/9223259

 

[nomadreid]

Thank you for your reply and the links, atyy.
If I understand correctly (no guarantee of that), all the links you sent all roughly say that it is a fuzzy area:
(1) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1692208/pdf/9533126.pdf leans towards "Biological Species Concept", similar to my rough definitions but nuanced due to unusual cases,
(2) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC33696/ leans more towards a phylogenetic interpretation of species whereby physical features are the primary criteria which are of course influenced by genetic isolation
(3) http://www.pnas.org/content/96/13/7117.long says that whichever concept you take, it is still not clear whether the Neanderthals were indeed a separate species.

 

[atyy]

Yes, that's my understanding too. On the last point, there is more recent DNA data that is discussed in eg. http://www.ncbi.nlm.nih.gov/pubmed/23055938 .

 

[thorium1010]

I learned that two sexual organisms are considered different species when no two organisms having their respective DNA structures could interbreed to produce viable offspring. Put another way, when looking it up, I find the definition:

Perhaps you have heard of ring specieshttp://en.wikipedia.org/wiki/Ring_species

(a) Neanderthal interbred with homo sapiens to give part of today's modern man
(b) Neanderthals is a different species from homo sapiens.

http://en.wikipedia.org/wiki/Neanderthal#Genome

On 16 November 2006, Lawrence Berkeley National Laboratory issued a press release suggesting Neanderthals and ancient humans probably did not interbreed.[69] Edward M. Rubin, director of the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the Joint Genome Institute (JGI), sequenced a fraction (0.00002) of genomic nuclear DNA (nDNA) from a 38,000-year-old Vindia Neanderthal femur. They calculated the common ancestor to be about 353,000 years ago, and a complete separation of the ancestors of the species about 188,000 years ago.[70]

Their results show the genomes of modern humans and Neanderthals are at least 99.5% identical, but despite this genetic similarity, and despite the two species having coexisted in the same geographic region for thousands of years, Rubin and his team did not find any evidence of any significant crossbreeding between the two. Rubin said, "While unable to definitively conclude that interbreeding between the two species of humans did not occur, analysis of the nuclear DNA from the Neanderthal suggests the low likelihood of it having occurred at any appreciable level

 

[nomadreid]

Thanks, atyy. Very interesting article.
thorium 1010: very interesting about ring species; no, I hadn't known.
As far as the other Wiki article you cited, the one you quoted, read a bit further down, where it says

However, an analysis of a first draft of the Neanderthal genome by the same team released in May 2010 indicates interbreeding may have occurred.

That cleared the way for the more recent articles (such as the article that atyy just cited) which continue to test the assumption that interbreeding may have occurred.

 

[thorium1010]

Thanks, atyy. Very interesting article.
As far as the other Wiki article you cited, the one you quoted, read a bit further down, where it says

That cleared the way nfor the more recent articles (such as the article that atyy just cited) which continue to test the assumptio that interbreeding may have occurred.

Sure, but would you call something 99.5% similar to us, a different species ? Thats the important question, where would draw the line for species ?

Species in biology is somewhat of a grey area, it is not black and white as we think it is.

 

[nomadreid]

Sure, but would you call something 99.5% similar to us, a different species ? Thats the important question, where would draw the line for species ?

Species in biology is somewhat of a grey area, it is not black and white as we think it is.

Indeed, that was my original question, and the answers showed me that it is indeed a fuzzy concept.

 

[ChrisJA]

I think the fact that there is small amounts of Neanderthal DNA in modern Europeans proves that Neanderthal were not a different species in the classic sense of "species".

I think what happened was that there was a minor amount of inner breading but mostly the Neanderthal were out competed. In those days, 30K yeas ago, I think the Neanderthal population would have been equilibrium with the food supply. Then come these other guys who like to eat the same food. We modern humans eat their food so they remained in equilibrium with a shrink food supply. And I'm sure there was a very rare hybrid born now and then.