Until about 150 years ago Nadars - mostly "toddy tappers" - were condemned to a near untouchable status.

BBC: Caste and entrepreneurship in India

Dr. Smits has started a company, Tapergie, employing more than 6, 000 local palm tappers to produce this truly sustainable biofuel.

FORBES: An Energy Crisis Solution That Proves Small Can Be Beautiful

The daughter of rubber tappers in the Amazon, she learned to read as a teenager and did some of the menial jobs that many Brazilians labour in before becoming a star of the international environmental movement.

ECONOMIST: Presidential politics in Brazil