This is a trick put there by God to test our faith. Besides, these godless scientists are inventing this to try to disprove the undeniable fact that the earth is 6,000 years old. Furthermore, there are layers of bent, stretched, and folded rock laid down all over the world. It's obvious that rock does not bend, stretch, or fold. Thus, it must have been laid down about 4,000 years ago in a world-wide flood.
In all seriousness, this is a fascinating discovery. If we compare humans to dogs, we note that humans are much more homogeneous. The largest man (barring the occasional medical exception) is generally about 200-250 lbs. The smallest adults would be the pygmies or certain little S.E. Asian ladies who weigh in at 80-100 lbs. A factor of 2-2.5. And yet when you look at that tiny Japanese lady standing next to the enormous Nigerian man, they look almost like different species. By contrast, the smallest adult dog (barring a few medical outliers) is 3-4 lbs, while a large mastiff may be 200 lbs. A factor of 50. In fact, by strict definition, a chihuahua and a mastiff might not even be considered the same species because, although they are genetically compatible, there's really no way they can mate without a lot of human intervention.
It seems that about 1-2k years ago, there was a genetic bottleneck for humans. It was a very dangerous time for our species. A plague or other natural disaster would have probably meant the end for intelligent life on Earth. All humans alive today seem to be descendants of just a few hundred to a few thousand people. Any less and there would have been too much inbreeding to maintain sufficient genetic diversity to sustain the species.
Imagine, for a moment, that the bottleneck hadn't happened. The most likely outcome would have been that humans would have differentiated into as many variations of "breeds" as dogs. The world of J.R. Tolkien would not be a fantasy, but closer to reality. There would be diminutive races of humans and gargantuan races of humans, all with different features, behaviors, health issues, lifespans, etc. Maybe we wouldn't have immortal elves and friendly, pudgy, skittish hobbits, but we wouldn't be too far off from that.
The question is whether we'd be able to get along as well as they seem to in the Lord of the Rings world. My guess is that, much as humans have done, entire races would be wiped out when a more adaptable race moved in, either by warfare, interbreeding, or sheer competition.
On the other hand, it would make filming World of Warcraft Elf Porn much cheaper.