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Evolutionary and adaptation of human pygmy of Flores Island

Penelitian - Two pygmy populations on the same tropical island, one went extinct tens of thousands of years ago; the other still lives there. Are they related? It's a simple question that took years to answer. As no one has been able to recover DNA from the fossils of Homo floresiensis (nicknamed the "hobbit"), researchers had to create a tool for finding archaic genetic sequences in modern DNA.

The technique was developed by scientists in the lab of Joshua Akey and the Lewis-Sigler Institute for Integrative Genomics at Princeton University. The scientists used this technique with the genomes of 32 modern pygmies living in a village near the Liang Bua cave on Flores Island in Indonesia, where H. floresiensis fossils were discovered in 2004.

Penelitian Evolutionary and adaptation of human pygmy of Flores Island

The results published on Science show insular dwarfism arose independently at least twice on Flores Island, first in H. floresiensis and again in the modern pygmies

"In your genome, and in mine, there are genes that we inherited from Neanderthals. Some modern humans inherited genes from Denisovans, another extinct species of humans, which we can check for because we have genetic information from Denisovans," said Serena Tucci of the Akey's lab.

"But if you want to look for another species, like Floresiensis, we have nothing to compare, so we had to develop another method. We 'paint' chunks of the genome based on the source. We scan the genome and look for chunks that come from different species, Neanderthal, Denisovans, or something unknown," Tucci said.

"They definitely have a lot of Neanderthal. They have a little bit of Denisovan. We expected that, because we knew there was some migration that went from Oceania to Flores, so there was some shared ancestry of these populations," said Tucci.

But there were no chromosomal "chunks" of unknown origins. The researchers did find evolutionary changes associated with diet and short stature. Height is very heritable and geneticists have identified many genes with variants linked to taller or shorter stature. Tucci and colleagues analyzed the Flores pygmy genomes with respect to height-associated genes identified in Europeans and they found a high frequency of genetic variants associated with short stature.

"If there was any chance to know the hobbit genetically from the genomes of extant humans, this would have been it. But we don't see it. There is no indication of gene flow from the hobbit into people living today." said Richard Green of the University of California-Santa Cruz (UCSC). Evolutionary and adaptation of human pygmy of Flores Island

"It sounds like a boring result, but it's actually quite meaningful. It means that these gene variants were present in a common ancestor of Europeans and the Flores pygmies. They became short by selection acting on this standing variation already present in the population, so there's little need for genes from an archaic hominin to explain their small stature," Green said.

The Flores pygmy genome also showed evidence of selection in genes for enzymes involved in fatty acid metabolism, called FADS enzymes (fatty acid desaturase). These genes have been associated with dietary adaptations in other fish-eating populations, including the Inuit in Greenland.

Fossil evidence indicates H. floresiensis was significantly smaller than the modern Flores pygmies, standing about 3.5 feet tall (106 centimeters, shorter than the average American kindergartener), while modern pygmies average about 15 inches taller (145 centimeters). Floresiensis also differed from Homo sapiens and Homo erectus in their wrists and feet, probably due to the need to climb trees to evade Komodo dragons.

Dramatic size changes in animals isolated on islands is a common phenomenon, often attributed to limited food resources and freedom from predators. In general, large species tend to get smaller and small species tend to get larger on islands. At the time of H. floresiensis, Flores was home to dwarf elephants, giant Komodo dragons, giant birds and giant rats, all of which left bones in the Liang Bua cave.

"Islands are very special places for evolution. This process, insular dwarfism, resulted in smaller mammals, like hippopotamus and elephants, and smaller humans. This is really intriguing, because it means that evolutionarily, we are not that special. Humans are like other mammals, we are subject to the same processes," Tucci said.

Journal : Serena Tucci et al. Evolutionary history and adaptation of a human pygmy population of Flores Island, Indonesia, Science, 03 Aug 2018, DOI:10.1126/science.aar8486



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