Denisovans Were Neanderthals’ Cousins, DNA Analysis Reveals

The entire genome of the Denisovans was extracted from a tooth and finger bone.

An international team of scientists has identified a previously shadowy human group known as the Denisovans as cousins to Neanderthals who lived in Asia from roughly 400,000 to 50,000 years ago and interbred with the ancestors of today’s inhabitants of New Guinea.

All the Denisovans have left behind are a broken finger bone and a wisdom tooth in a Siberian cave. But the scientists have succeeded in extracting the entire genome of the Denisovans from these scant remains. An analysis of this ancient DNA, published on Wednesday in Nature, reveals that the genomes of people from New Guinea contain 4.8 percent Denisovan DNA.

An earlier, incomplete analysis of Denisovan DNA had placed the group as more distant from both Neanderthals and humans. On the basis of the new findings, the scientists propose that the ancestors of Neanderthals and Denisovans emerged from Africa half a million years ago. The Neanderthals spread westward, settling in the Near East and Europe. The Denisovans headed east. Some 50,000 years ago, they interbred with humans expanding from Africa along the coast of South Asia, bequeathing some of their DNA to them.

“It’s an incredibly exciting finding,” said Carlos Bustamante, a Stanford University geneticist who was not involved in the research. …

via Denisovans Were Neanderthals’ Cousins, DNA Analysis Reveals – NYTimes.com.

Milky Way’s Galactic Neighbourhood Puzzles Astronomers

There’s something odd about our galactic neighbourhood, which Sidney van den Bergh at the Herzberg Institute of Astrophysics in Canada highlights today in a short paper.

Astronomers have long known that the Milky Way’s two closest neighbours are the Large and Small Magellanic Clouds, giant clouds of stars, gas and dust called irregular galaxies.

This is strange for two reasons. These galaxies are much younger than ours and may have even formed together. It looks as if they may just be passing by, on their way to somewhere else. Most other galaxies like ours, such as Andromeda, don’t have a single companion like this, so having two seems rather fortunate.

But there’s something else as well. The Large Magellanic cloud is unusually luminous. In fact, there are only two other irregular galaxies in the entire local universe that come close. “In other words the Large Magellanic Cloud seems to be close to the upper luminosity limit for irregular galaxies,” says van den Bergh. That’s unusual too.

In recent years, astronomers have begun to work out just how rare this is. Sky surveys such as the Sloan Digital Sky Survey allow astronomers to work out the distribution of various types of galaxy. They’ve looked at 22581 galaxies like the Milky Way and found that 81% have no satellite galaxies as bright as the Magellanic Clouds, 11% have one such satellite, and only 3.5% host two such satellite galaxies. …

via Milky Way’s Galactic Neighbourhood Puzzles Astronomers  – Technology Review.