Ilka Hartmann · Public domain

A Stanford population biologist who spent decades studying butterflies before turning his 1968 book The Population Bomb into one of the most argued-over works of postwar science writing, warning that unchecked population growth would outstrip the planet's resources. He helped lead the effort to preserve Stanford's Jasper Ridge as a research reserve in 1973. His specific famine predictions did not come to pass, and critics have long disputed his methods, but he maintained his warnings about overconsumption, disease, and climate change held up.