Bodies keep shrinking on this island
FIFTEEN YEARS AFTER BONES WERE FOUND, STUDY DELIVERS AN IMPORTANT VERDICT
In 2003, researchers digging in a mountain cave on the Indonesian island of Flores discovered astonishing fossils of a tiny, humanlike individual with a small, chimpsized brain. They called the species Homo floresiensis.
These relatives of modern humans stood just over 90 centimetres tall. Several villages in the area, scientists noted, are inhabited by people whose average height is 1.4 metres.
Was this the result of interbreeding long ago between taller modern humans and shorter Homo floresiensis?
Fifteen years after the bones’ discovery, a study of the DNA of living people on Flores has delivered a verdict.
“It’s rare in science that you set about to answer a question and you get something of a definitive answer and it’s the end,” said Richard E. Green, a geneticist at the University of California, Santa Cruz, and a co-author of the study, published Thursday in Science.
“The answer is a clear enough ‘no’ that I’m done with it.”
But as often happens in science, the answer to one question raises new ones. The study shows that at least twice in ancient history, humans and their relatives (known as hominids) arrived on Flores and then grew shorter.
And not just humans: Other research has shown that elephants also arrived on Flores twice, and both times the species evolved into dwarves.
So what mysterious power does this island have to shrink the body?
When the fossils of Homo floresiensis first came to light, many researchers hoped they might still hold fragments of DNA. They were encouraged by the initial dating of the fossils — an estimated age of perhaps just 13,000 years.
Compared to living people
DNA analysis might have settled the debate over how Homo floresiensis fits into the hominid family tree.
In 2007 Herawati Sudoyo, a geneticist at the Eijkman Institute for Molecular Biology in Indonesia, brought samples of Homo floresiensis fossils to Green, then at the Max Planck Institute for Evolutionary Anthropology in Germany.
Hard as he and his colleagues tried, they failed to get any definitive DNA from the fossils.
“We could never really make sense of it,” said Green.
Enlisted by Sudoyo, Dr. Serena Tucci, now a postdoctoral re- searcher at Princeton University, and her colleagues compared the DNA of the Rampasasa villagers to that of other living people around the world.
The researchers found that a very small percentage of the villagers’ DNA came from Neanderthals or Denisovans. A tiny portion could not be matched to humans, Neanderthals or Denisovans. But these enigmatic pieces were not dramatically different from human DNA, as you would expect if they had come from Homo floresiensis. Tucci concluded that the Rampasasa villagers have no Homo floresiensis ancestry.
“I wasn’t disappointed,” she said, “because they are extremely interesting for other reasons.”
Rampasasa villagers are not short because they descend partly from Homo floresiensis. Instead, their ancestors were taller humans. But at some point after they came to Flores, they became very short — as did Homo floresiensis before them. And they are not the only mammals to have shrunk.
Those dwarf elephants on Flores, now extinct, were only as tall at the shoulder as a human. Judging from related species elsewhere in Southeast Asia, their ancestors were likely full sized.
One leading hypothesis for the evolution of the pygmy body type is a shortage of food. A smaller body demands fewer calories and may offer a survival advantage.
“Whatever the ecological factors are for island dwarfism are, they are present in spades on this island,” Green said of Flores. “That’s what makes it so fascinating.”