The menopause is a puzzle for biologists. Why would the female of a species cease to reproduce half way through her life, when natural selection favours characteristics that help an individual's genes survive? A study of killer whales - one of only two mammals apart from humans to undergo the menopause - is providing clues. Granny is very spritely for a centenarian. When I finally catch sight of San Juan Island's local celebrity, she leaps clear out of the ocean to delighted gasps from everyone on my boat. Granny is a killer whale, or orca. She lives in a coastal area of the North Pacific, close to Vancouver and Seattle, known as the Salish Sea. And while she is affectionately known as "Granny", her formal name is J2 - an alpha-numeric title that identifies her as a member of a population known as the Southern Resident orcas. It is a clan of 83 killer whales in three distinct pods - J, K and L-pod - all of which return to this area of coastal Pacific waterways ...