How can Neanderthal and Homo Sapiens interbreed?

Speciation does not require the loss of the ability to interbreed, although eventually that usually happens. Inability to interbreed is necessary for speciation to occur in the first place, but this can be the result of a geographic barrier (such as a river or a mountain range) or lack of desire to interbreed, not necessarily the genetic inability to interbreed.

Viewing them as separate species is what's causing the confusion. And while they are separate species, they represent two different branches of the same tree. Neanderthals were close enough to us genetically, that 99 percent of our DNA was the same. Remember, lions and tigers can be interbred also, and they are different species. Note: The place of interbreeding was most likely the Middle East, nor Europe (per the scientists who published the paper).

may be they weren't two different species but two different breeds such as dogs thus this would explain the different appearances but with still the ability to breed ,by this i mean that they had not changed enough to be two distinct species[dingoes and domestic dogs]

It does appear as if non Africans got a few neanderthal genes from neanderthal males. MtDNA shows no neanderthal DNA but recent sequencing "appears" to indicate sapien outside of Africa scarfed up from 1 to 4% of their genes from neanderthal. Some interbreeding as well as plain old competition for food sources and land would have led to the neanderthal's demise. Both neanderthal & sapien karyotypes show the same number of chromosomes .so,we cannot deny the view that there could have been Neanderthal and Homo sapien interbreeding . http://www.nature.com/nature/journal/v444/n7117/fig_tab/nature05336_F4.html See this pic...both sapiens and neanderthals have same ancestor . http://www.iupui.edu/~mstd/a103/Human%20Origins%20Chart_files/iskull.gif http://www.sciencenews.org/view/generic/id/58936/title/Neandertal_genome_yields_evidence_of_interbreeding_with_humans

It's almost certain that the two species inherited the same genes from a common ancestor rather than from being interbred. By definition two separate species cannot interbreed. Since HN was about 300,000 yr old as a species it could not interbreed with humans in the short time they shared a common habitat. Previous to humans leaving Africa the two species had been entirely separated.

When science get their conclusions to serious questions by guesswork such as you have related then I do not wonder that anthropology is in such a state. So, Amanda Drawry, I think it is time we all went back to the beginning, long before the Cambrian Explosion 530 million years ago ( when all life is reputed to have begun seriously ) and start our quest all over again.

Don't think of them as two entirely different species. More like steps on the evolutionary ladder. At some point, homo sapiens evolved from neanderthals, but it wasn't an instant, global change. Hope that answered your question :),

I think you have just answered your own question. Good girl Amanda.