then, as the world warmed, numbers began to dwindle and it retreated to northern siberia. for the -- 4000 years ago, it died out completely. but why? and new study shows that as the world war and at the height of the last ice age, -- as the world warmed, at the height of the last ice age, grasslands on which the mammoth depended disappeared. >> we have mammoth bones as evidence. what this shows is the things that drove the mammoths to the brink of extinction was the loss of habitat and loss of grazing. >> so climate change, and the consequent lack of food, rather than humans, led to the demise of the woolly mammoth. bbc news. >> good to have you with us on "bbc world news." do stay, if you can. still to come -- vietnam's internet police. can they maintain the online boom? first though, is 100 days since david cameron injured downing street as prime minister with nick clegg as his deputy. they are still promising new policies and tough choices. but are the old divisions resurfacing? >> tricky, it may be, but the members of the coalition appeared to be happy working together