Jpedreira · CC BY-SA 2.5

Proposed that the complex cells making up plants, animals, and fungi arose when free-living bacteria merged symbiotically — a theory so far outside the mainstream that her founding 1967 paper was rejected by roughly fifteen journals before publication, and largely ignored for another decade until genetic evidence proved it out. She later co-developed the Gaia hypothesis with James Lovelock. Elected to the National Academy of Sciences in 1983, she received the National Medal of Science from President Clinton in 1999.