World News from the BBC

There have been new calls for the release of the BBC journalist Urunboy Usmonov, who was detained in Tajikistan last month on charges that he is a member of a banned Islamic group.

Amnesty International and Europe's human rights body, the OSCE, said he must be freed immediately.

Amnesty said that Usmonov appeared to have been tortured while being held by the Tajik authorities. The BBC says the allegations against Mr Usmonov are unfounded.

The Egyptian authorities have charged 25 people in connection with an attack on protesters in Tahrir Square

at the height of

the Egyptian revolution earlier this year. Supporters of the then President Hosni Mubarak

mount

ed on camels and horseback forced their way through the crowds, injuring many of the demonstrators and sparking violent clashes. Those indicted include Fathi Sorour, the former speaker of parliament, and Safwat el-Sherif, who headed the former ruling party.

Research by an international team of scientists has found that all polar bears

descend

from a single female brown bear. It lived between 20,000 and 50,000 years ago in what is modern-day Ireland. Tim de Valmont has the details.

Polar bears and brown bears became

distinct

species around 150,000 years ago, but have occasionally interbred ever since. The research used DNA samples from bears from across their entire range in Russia, Canada, Greenland, Norway and Alaska. This mother of all bears may show that interbreeding, which had been thought to have threatened the species, may have actually played a key role in helping the polar bear to evolve. There are currently around 20,000 polar bears left living in the wild.