Conservationist Dame Jane Goodall, a world-leading expert on chimpanzees, has died aged 91.

Her observations helped to reveal how closely related humans are to chimpanzees. She also worked tirelessly for conservation projects around the world.

Dr. Goodall died of natural causes while in California on a speaking tour of the US, according to a statement from the Jane Goodall Institute.

It said her discoveries revolutionised science and that she was a tireless advocate for the protection and restoration of our natural world.

The United Nations said it mourned the loss of Dr. Goodall, saying that she worked tirelessly for our planet and all its inhabitants, leaving an extraordinary legacy for humanity and nature.

Greenpeace expressed it was heartbroken by her death, calling her one of the true conservation giants of our time. Will McCallum, its co-executive director in the UK, noted: Dr Goodall's legacy is not only in science but in the global movement she helped spark to protect nature and give hope for a better world.

Naturalist Chris Packham told the BBC that he counted her among his heroes, calling her revolutionary and remarkable. To have lost a hero at a time when we need all of them on the frontline fighting for life on earth is a tragedy, he added.

Born in 1934 and raised in London, Dr. Goodall became fascinated by animals after reading books such as The Story of Dr. Doolittle and Tarzan. She met leading primatologist Prof. Louis Leakey in her mid-twenties, who saw her potential despite her lack of qualifications and helped arrange her first research trip to Tanzania in 1960.

During her first fieldwork, she became the first person to record witnessing an animal using a tool, leading to significant changes in scientific perceptions of intelligence among non-human animals.

Dr. Goodall's work was extensively published, culminating in a famous feature on the cover of National Geographic in 1965. She showcased the emotional and social lives of primates and emphasized the importance of conservation.

Throughout her life, Dr. Goodall continued to advocate for animal rights, conservation, and climate action, fostering a movement dedicated to protecting the planet's biodiversity.

Her Jane Goodall Institute, founded in 1977, focuses on protecting chimpanzees and benefiting both animals and the environment. She remained active and engaged until her passing, having been on a speaking tour in recent weeks.