To the untrained eye, Skipper and Ping look like a typical king penguin couple. Standing side by side at the Berlin Zoo with their flippers touching, they take turns carefully nestling an egg between their feet in the hope that it will eventually hatch the chick they have both long sought. Except these two 10-year-olds are both male — and the latest in a long succession of same-sex penguins that have coupled up to adopt an egg. At zoos in London, Australia and New York, male and female penguins have for years entered same-sex relationships to incubate eggs into chicks, delighting zookeepers and some visitors while stirring anger and revulsion in others.