It s one of the oldest jokes in the book, but the answer to ~Why don t polar bears eat penguins?
may need to be revised.
Until recently, very few species have been known to be found at both poles. It was thought that this was due to the warm tropics acting as a barrier to organisms adapted to the polar environments. The exceptions to the rule including several species of whale, and some migratory birds.
However, scientists working for the Census of Marine Life have found at least 235 species which live in both Arctic and Antarctic seas despite a distance of 11,000 kilometres between them.
Species living at both poles include worms, crustaceans, sea cucumbers and pteropods. Of particular interest was a swimming snail which ~spins a mucus net to catch food, a carnivorous pteropod which feeds exclusively on its ~relatives, and a crustacean known as an ~oar foot .
Studies are currently underway to analyse the DNA of the species at the different poles to find if they are actually the same species or merely ones which look identical. If they do turn out to be identical there are various theories as to how they ended up so far apart.
Amongst these theories are that larvae from the Antarctic were swept north to the Arctic along the cooler, deep ocean floor thereby avoiding the warm tropical waters; dispersal during ice ages; or even being transported by whales, birds or ships. Further genetic studies will reveal the answer to these questions.
Among many other findings, the scientists also documented evidence of coldwater loving species shifting towards both poles to escape rising ocean temperatures.
In addition the survey of the Antarctic found a fish known as an ice fish Chionodraco hamatus which has a special type of antifreeze in its blood allowing it to withstand temperatures which would freeze the blood of other fish.
The survey of the poles has so far revealed 7,500 species in the Antarctic and 5,500 in the Arctic. Full results of the Census of Marine Life will be released in October 2010.
Back to the original question however, the answer to the joke is of course ~because they can t get the wrappers off ...