A 700,000-year-old arm bone found on an Indonesian island sheds light on the evolution of... Homo floresiensis 1– an ancient relative of modern humans, nicknamed Hobbit due to his small size.

The arm bone fragment, just 88 millimeters long, was among the smallest adult hominids ever found. The discovery, published August 6 inNature Communications, supports the idea that the ancestors ofH. floresiensisevolved into a much smaller species just a few thousand years after arriving on the remote island of Flores in what is now Indonesia.

Island dwarfism – the process by which animals develop smaller body size through isolation on an island – has occurred frequently during evolution. But before that Discovery ofH. floresiensis, which was reported in 2004 2, 3, no one thought it could happen to humans,” says study co-author Yousuke Kaifu, an anthropologist at the University of Tokyo.

The assumption that the ancestors ofH. floresiensisThe fact that they could have developed dwarfism so quickly after arriving on the island is “surprising but also exciting,” he adds.

Island effect

Species trapped on an island often undergo massive changes to adapt to their new environment. Mammoths, deer and other animals that have ended up on islands have all dwindled - possibly because there is less food available or because there are fewer threats from predators, Kaifu says.

Scientists suspect that something similar happened with the ancestors ofH. floresiensiscould have happened. A working…

Ein Bild des Humerusfragments von Mata Menge neben dem Humerus von Homo floresiensis aus Liang Bua, als Maßstab

A breakthrough came in 2015 when the team reconstructed fragmented bones in the lab and found that some broken pieces belonged to a humerus - the bone that connects the shoulder to the elbow. Although the fossil was missing both end pieces, it could still provide some clues about the size of the ancient human to whom it belonged.

Adult bone

The size of the humerus suggested that its owner was tiny - but it could also have belonged to a child rather than an adult. In the latest study, Kaifu and his team examined a piece of the bone under a microscope to investigate this possibility. The structure of the bone suggested that it belonged to a fully grown adult.

The arm bone is 9-16% smaller and thinner than those 60,000 years oldH. floresiensisspecimen belonged, confirming that its owner was “at least as small as later members of the species,” says Baab. The researchers estimate that this person would have been no more than 108 centimeters tall.

The results suggest thatH. floresiensisevolved into a shorter species within 300,000 years after the species' ancestors arrived on the island. Brain findings fromH. floresiensis suggest that their brains also shrank during this time. The rapid emergence of a new body type shows the many paths human evolution can take, Kaifu says. “We believe that it was people’s destiny to become smart,” he says. “Flores shows us that there are other ways for people to be.”