Enlarge (credit: Jarcosa)

Rapa Nui, often referred to as Easter Island, is one of the most remote populated islands in the world. It's so distant that Europeans didn't stumble onto it until centuries after they had started exploring the Pacific. When they arrived, though, they found that the relatively small island supported a population of thousands, one that had built imposing monumental statues called moai. Arguments over how this population got there and what happened once it did have gone on ever since.

Some of these arguments, such as the idea that the island's indigenous people had traveled there from South America, have since been put to rest. Genomes from people native to the island show that its original population was part of the Polynesian expansion across the Pacific. But others, such as the role of ecological collapse in limiting the island's population and altering its culture, continue to be debated.

Researchers have now obtained genome sequence from the remains of 15 Rapa Nui natives who predate European contact. And they indicate that the population of the island appears to have grown slowly and steadily, without any sign of a bottleneck that could be associated with an ecological collapse. And roughly 10 percent of the genomes appear to have a Native American source that likely dates from roughly the same time that the island was settled.

Enlarge / Half of the upper arm bone of this species can fit comfortably in the palm of a modern human hand. (credit: Yousuke Kaifu)

The discovery of Homo floresiensis, often termed a hobbit, confused a lot of people. Not only was it tiny in stature, but it shared some features with both Homo erectus and earlier Australopithecus species and lived well after the origin of modern humans. So, its precise position within the hominin family tree has been the subject of ongoing debate—one that hasn't been clarified by the discovery of the similarly diminutive Homo luzonensis in the Philippines.

Today, researchers are releasing a paper that describes bones from a diminutive hominin that occupied the island of Flores much earlier than the hobbits. And they argue that, while it still shares an odd mix of features, it is most closely related to Homo erectus, the first hominin species to spread across the globe.

Remarkably small

The bones come from a site on Flores called Mata Menge, where the bones were found in a large layer of sediment. Slight wear suggests that many of them were probably brought to the site by a gentle flood. Dating from layers above and below where the fossils were found limits their age to somewhere between 650,000 and 775,000 years ago. Most of the remains are teeth and fragments of jaw bone, which can be suggestive of body size, but not definitive. But the new finds include a fragment of the upper arm bone, the humerus, which is more directly proportional to body size.

Enlarge (credit: Halamka)

The basic outline of the interactions between modern humans and Neanderthals is now well established. The two came in contact as modern humans began their major expansion out of Africa, which occurred roughly 60,000 years ago. Humans picked up some Neanderthal DNA through interbreeding, while the Neanderthal population, always fairly small, was swept away by the waves of new arrivals.

But there are some aspects of this big-picture view that don't entirely line up with the data. While it nicely explains the fact that Neanderthal sequences are far more common in non-African populations, it doesn't account for the fact that every African population we've looked at has some DNA that matches up with Neanderthal DNA.

A study published on Thursday argues that much of this match came about because an early modern human population also left Africa and interbred with Neanderthals. But in this case, the result was to introduce modern human DNA to the Neanderthal population. The study shows that this DNA accounts for a lot of Neanderthals' genetic diversity, suggesting that their population was even smaller than earlier estimates had suggested.

Enlarge / The Baishiya Karst Cave, where the recently analyzed samples were obtained. (credit: Dongju Zhang’s group (Lanzhou University))

For well over a century, we had the opportunity to study Neanderthals—their bones, the items they left behind, their distribution across Eurasia. So, when we finally obtained the sequence of their genome and discovered that we share a genetic legacy with them, it was easy to place the discoveries into context. By contrast, we had no idea Denisovans existed until sequencing DNA from a small finger bone revealed that yet another relative of modern humans had roamed Asia in the recent past.

Since then, we've learned little more. The frequency of their DNA in modern human populations suggests that they were likely concentrated in East Asia. But we've only discovered fragments of bone and a few teeth since then, so we can't even make very informed guesses as to what they might have looked like. On Wednesday, an international group of researchers described finds from a cave on the Tibetan Plateau that had been occupied by Denisovans, which tell us a bit more about these relatives: what they ate. And that appears to be anything they could get their hands on.

The Baishiya Karst Cave

The finds come from a site called the Baishiya Karst Cave, which is perched on a cliff on the northeast of the Tibetan Plateau. It's located at a high altitude (over 3,000 meters or nearly 11,000 feet) but borders a high open plain, as you can see in the picture below.