Lemurs are animals unique to Madagascar. They have been isolated on this vast island off the south-east coast of Africa for twenty million years. Shy, gentle, and in some cases beautiful creatures, they have in time been hunted by the Malagasy people as food and feared as reincarnations of the dead. An Oxford University Expedition has completed a two-month field study and for the first time a great deal of lemur behaviour has been recorded on film.

Today is the 200th anniversary of the birth of this famous scientist and writer, best-known for his prodigious four-year journey across South America and for the Pacific current which bears his name. Foremost among the many Latin-American nations to celebrate this event will be Mexico, visited by Humboldt in 1803-4 and where he is revered as one of the founders of the country's independence from Spain.

In this birthday tribute Robert Cundy follows Humboldt's route across Mexico from ocean to ocean, Acapulco to Vera Cruz. He descends silver mines and climbs recently erupted volcanoes to present a portrait of a country whose diverse landscape and mysterious past presented an irresistible challenge to a scientist and humanist fascinated by everyone and everything.