New research shows that two populations of small-bodied hominins arose independently on the Indonesian island of Flores.
The study, published in the journal Science, reveals that no genetic exchange took place between the tiny extinct hominin species Homo floresiensis, which once inhabited Flores, and the ancestors of a group of extremely short-statured humans who live there today.
The remains of H. floresiensis, or the “Flores Hobbit”, were first discovered in the Liang Bua cave on the island in 2003. Intriguingly, the remains were those of a mature adult who would have stood just one metre tall.
Evidence suggests H. floresiensis lived on the island between 60,000 and at least 100,000 years ago. Yet the nature of their relationship to modern humans remains a mystery, in part because no Hobbit DNA has ever been recovered.
Today, several dozen families live in the nearby hamlet of Rampasasa, the overwhelming majority of whom are extremely small, with an average height of around 145cm.
Their small stature and close proximity to the Liang Bua site prompted suggestions that somewhere in their ancestral history, genetic intermixing with the archaic hominins may have occurred.
To shed light on the history of hominin presence on Flores, and perhaps get a glimpse of H. floresiensis DNA, Richard Green at the University of California Santa Cruz and Serenea Tucci at Princeton University, both in the US, examined the genomes of individuals from Rampasasa.
In collaboration with scientists in the US, Europe, Australia and Indonesia, they searched for small genetic differences, called single nucleotide polymorphisms (SNPS), in the genomes of 32 Rampasasan adults, and sequenced the entire genomes of 10 of them.
There was no evidence of H. floresiensis DNA.
“If there was any chance to know the Hobbit genetically from the genomes of extant humans, this would have been it,” says Green. “But we don’t see it.”
“Genetically, they’re not so different from other populations in that part of the world,” he says of the Rampasasan individuals.
Indeed, their genomes appear to be a mixture of ancestry associated with East Asian, New Guinean and Oceanic populations.
As is common in these groups, the Rampasasan genomes include small amounts of DNA from Neanderthals and Denisovans, who were archaic humans.
The analysis did reveal some particularly distinctive genetic hallmarks, though.
“The most interesting result was evidence for adaptation, both diet-related and for reduced stature,” say Peter Visscher of the University of Queensland, Australia, who was also involved in the study.
For example, Rampasasan individuals possess a high frequency of variations in a cluster of genes involved in fatty acid synthesis.
“This is consistent with an ancestral change towards a more marine diet rich in omega-3 fatty acids,” says Visscher.
Similar adaptations in this area of the genome have been found in Inuit people of Greenland.
Environmental adaptation also appears to be responsible for the Rampasasans’ body size.
By accessing the UK Biobank, the researchers were able to examine genomic data of more than 450,000 people of European ancestry, and identified numerous variations linked with reduced height. When they searched for these variations in the Rampasasan genomes, they found not just one, but many.
“It sounds like a boring result, but it’s actually quite meaningful,” says Green.
It suggests that genetic variations for short stature go back all the way to a common ancestor of Europeans and the families currently living in Rampasasa. For the latter, the selective pressure was most likely provided by the island itself.
The “Island Rule” is a phenomenon whereby large mammals on islands gradually get smaller over long periods of time, and has been well documented for a range of animals. Indeed, there is evidence that a species of tiny elephants also once existed on Flores.
“Weird things happen on islands,” says Green. “With the gene pool cut off from the larger population, an island population is free to evolve in unrestrained directions based on the demands of a small ecosystem.”