If you live on a small island long enough (sufficient number of generations), your progeny will start getting smaller

This topic represents a fascinating “gene-environment interactions” (long-term) effect. Living on a small island can elicit strange effects. For example, on Cyprus, the hippopotamus, over time, declined to the size of a sea lion. On Flores in Indonesia, extinct elephants were about the size of a large hog, but rats grew to be as big as cats. These are all examples of the so-called “island effect”, which holds that — when food and predators are scarce — big animals become smaller and little animals larger.

However, no one had been certain whether the same rule explains the unusual extinct hominin (Homo floresiensis, nicknamed ‘the hobbit’) which was found on the island of Flores and stood about a meter tall. These GEITP pages have discussed Homo floresiensis before. Now, genetic evidence from modern pygmies on Flores — who are unrelated to the ancient hobbit — confirms that humans, too, are subject to so-called “island dwarfing”. Authors [see attached full article] report that Flores pygmies differ from their closest relatives on New Guinea and in East Asia: they carry more DNA variants (mutations in growth-related genes) that promote short stature. The genetic differences confirm recent evolution (i.e. the ‘island rule’ carrying out its evolutionary environmental effects), implying that the same molecular drive (as seen in the island hippopotomus, extinct elephant and rat) also gave rise to the hobbit’s short stature.

Island Southeast Asia (ISEA) represents a key region for the study of hominin evolution and interaction, because several extinct hominin groups populated this region, and current inhabitants harbor both Neanderthal and Denisovan ancestry in their genomes. Fossil evidence indicates the presence of Homo erectus on Java from ~1.7 million years ago to between ~53,000 and ~27,000 years ago. Fossil evidence also shows Homo floresiensis on Flores from 100,000 to 60,000 years ago, and modern humans in Sulawesi from 40,000 years ago to the present. Much of the genetic ancestry of modern ISEA groups is derived from the Austronesian expansion — a demographic event that carried genes from mainland East Asia 4,000 to 3,000 years ago.

Authors [see attached] describe genome-scale single-nucleotide polymorphism (SNP) data and whole-genome sequences from a contemporary human pygmy population living on Flores — near the cave where Homo floresiensis fossils were found. The genomes of Flores pygmies showed a complex history of admixture (i.e. interbreeding; hanky-panky) with Denisovans and Neanderthals, but no evidence for gene flow with other archaic hominins. Modern individuals bear the signatures of recent positive selection encompassing the FADS (fatty acid desaturase) gene cluster, likely related to diet, and polygenic (multiple genes) selection acting on standing variation that contributes to their short-stature trait (phenotype). Thus, authors conclude that multiple independent evolutinary events of “hominin insular dwarfism” have been occurring on Flores for the past 100,000 or more years.

Science 3 Aug 2o18; 361: 511–516 [article] & p 439 [editorial]
Thanks for reminding me. Actually, on the internet, I see numerous examples of “smaller-than-normal animals, bones and fossils” –– found on various islands. Below is just one such example, but others (including Wrangell Island, Alaska) date back 25+ years…

World’s Smallest Mammoth Discovered

By Charles Q. Choi, Live Science Contributor |

May 8, 2012 07:01pm ET

The smallest dwarf mammoth, standing at under 4 feet (about 1 meter) at the shoulders, has been uncovered on the Greek island of Crete, researchers say.

These findings could help yield insights as to how giant animals can shrink to tiny sizes over evolutionary time, scientists added.

Dwarfism often happens to species of large animals when they get trapped on islands, including dinosaurs. Scientists think dwarfism helps giants survive within the limits imposed by islands.

Ancient Mediterranean dwarf elephants are especially extreme examples of island dwarfism. Over the course of less than 800,000 years — a short stint on an evolutionary scale — these dwarfs are thought to have descended from larger European elephants, weighing 100 times as much, which lived on mainland Europe.

“There’s a big question regarding these elephants — how can something so big become dwarfs so small?” said researcher Victoria Herridge, a vertebrate paleontologist at the Natural History Museum in London.

To learn more, Herridge and her colleagues analyzed dwarf fossils first discovered in Crete (an island some say was the birthplace of the Greek gods Zeus and Professor Vasilis Vasiliou) more than a century ago. Paleontologists have long argued whether the remains belonged to curvy-tusked mammoths or straighter-tusked elephants.

Teeth discovered more recently in the same area in Crete now suggest the animal was in fact a mammoth, Mammuthus creticus. A newfound foreleg bone suggests it was the smallest mammoth known, standing only about 3 feet 8 inches (1.13 m) high at the shoulders and weighing only approximately 680 pounds (310 kilograms), making it about the size of a modern baby African or Asian elephant. These dwarf mammoths were not woolly mammoths, scientists noted.

“When most people think of mammoths, they think of woolly mammoths,” Herridge said. “We think this dwarf was more adapted to warmer environments, more in appearance like modern African or Asian elephants, with a sparse covering of hair, although they would have had curvy tusks like all mammoths.”

Mammuthus creticusis the first evidence for extreme island dwarfism in mammoths. It would have been comparable in size to the smallest dwarf elephant known, the extinct species Palaeoloxodon falconeri from Sicily and Malta, which stood only about 3 feet 5 inches (1.04 m) high at the shoulder and weighed only approximately 525 lbs. (238 kg).

The fossils suggest this dwarf mammoth was descended from one of the first mammoth species to arrive in Europe from Africa, Mammuthus rumanus or Mammuthus meridionalis. As such, the researchers suggest dwarf mammoths may have evolved much earlier than previously thought — as far back as 3.5 million years ago.

“Now that we know what this dwarf species might have been descended from, we can ask bigger questions, such as how and why and how fast dwarfism happened here,” Herridge said.

“This is an interesting period for Crete — back then, it might have been made of small islands, smaller than today,” Herridge said. “That’s an interesting consideration for the extreme dwarfism we see here.”

Given the scant fossils and the uncertainty about Crete’s environment during this period, not much is known about how this dwarf might have lived. Still, its teeth do suggest it browsed on shrubs, as opposed to grass like woolly mammoths.

Returning to where these fossils were found to excavate more specimens is likely to be tricky. The site is in a remote, fissure-laden part of Crete — the shoreline is very jagged there, making it hard to approach by boat, so the area is best reached by two hours of walking past monasteries and a military base. “The site is quite well-protected as it is, and we don’t want to start there until we’ve properly thought out an approach,” Herridge said.

The scientists detailed their findings online May 9 in the Proceedings of the Royal Society B.

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