It's useful in this context, after reading the BBC story kindly submitted here, to go to a webpage by a biology professor, Jerry Coyne, who literally wrote the book on speciation and definitions of species.[1] He wrote, in his webpage follow-up to a professional lecture for other biologists,[2]

"But I want to discuss briefly a shorter second piece by Gibbons in the same issue of Science, 'The species problem.' Here she brings up the controversy about whether modern humans, Neandertals, and Denisovans were members of different species or the same species. This question is far more important in dealing with humans than, say, with fruit flies, simply because there were far fewer types of hominins, and anthropologists’ careers depend on whether or not they name a new species. That’s why there are so many species names in the hominin family tree—names that turn on characters as tiny as a few millimeters in the measurement of a tooth. It’s likely that, several million years ago, three or four species of hominin did exist at the same time—and maybe at the same place—giving rise to fanciful scenarios about war and (especially) inter-group mating. . . .

"But that was more than a million years ago. What about the more modern groups of Homo, like Neandertals? According to Ernst Mayr’s biological species concept, which Gibbons describes, individuals are members of the same species if they can mate with each other when they encounter each other in nature, and, critically, produce fertile, viable hybrids. If they can’t, then there must exist genetic barriers to mixing of genes, the so-called 'reproductive isolating barriers' that maintain the integrity of species."

With that issue clarified, we see that anthropologists who find bones in the ground will always have incentive to be "splitters," identifying more rather than fewer species, and the only way to resolve how many species there were is to figure out which ancient hominids could mate and produce viable offspring who in turn could mate again and again produce viable offspring for more generations.

Studies of ancient DNA used to be impossible. It was a big breakthrough the first time an Egyptian mummy (plainly a modern human) had its DNA sequenced. The DNA sequencing of a Neanderthal[3] was a further breakthrough. It's plain now that Neanderthals and "modern humans" were part of the same biological species. The usual reckoning is that any modern human with traceable ancestry to Europe or to Asia probably has genes and gene combinations characteristic of Neanderthals, which have since spread further all over the world.

We are all closely related, and we are related to a great variety of ancient human fossil samples. Where human artifacts and cultural ideas travel, human genes travel, and we are all much more "mixed" and interrelated than people imagined even a decade ago.[4]

[1] Speciation by Jerry A. Coyne and H. Allen Orr

http://www.sinauer.com/speciation.html

[2] "How many species of humans were there?"

https://whyevolutionistrue.wordpress.com/2011/01/28/how-many...

[3] http://humanorigins.si.edu/evidence/genetics/ancient-dna-and...

[4] "Towards a new history and geography of human genes informed by ancient DNA"

http://biorxiv.org/content/biorxiv/early/2014/03/21/003517.f...